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Cholesterol is an important component of fresh biological baits and essential precursor to synthesize steroid hormones for crustacean. However, the cholesterol demand in Pacific white shrimp broodstock and its roles on ovary development and reproductive capacity are unknown. In the present study, female Pacific white shrimp broodstock (initial weight 51.3 ± 0.5 g) were fed with three diets contained 0.5 %, 1 % or 1.5 % cholesterol for 45 days. The results found that dietary cholesterol levels did not affect survival rate, weight gain, egg-laying number, vitellogenin content and vitellogenin receptor gene expression in the hepatopancreas. However, the hepatosomatic index, gonadosomatic index, egg diameter, vitellogenin level in the ovary and fertilized egg, C22:6n-3 (DHA) level in the fertilized egg, total protein, triglyceride and cholesterol contents were all increased in the 1.0 % and 1.5 % cholesterol groups than those in the 0.5 % cholesterol group. Moreover, compared with the 0.5 % and 1.0 % cholesterol groups, the 1.5 % cholesterol group had significantly higher gonad maturation number, mating rate, estradiol level in the hemolymph, steroid hormones synthesis related genes (HMGCR, StAR, 17βHSD and 1vMFBP) expression in the ovary and hepatopancreas. In conclusion, dietary 1.5 % cholesterol could promote ovary development and reproductive capacity in female Litopenaeus vannamei broodstock by improving nutrients accumulation and steroid hormones synthesis pathway. Our results provide guidance for design of artificial compound feed and healthy development of shrimp broodstock farm.

Vibrio genus is a common pathogen in aquaculture and causes acute hepatopancreatic necrosis disease (AHPND) and massive mortality of shrimp. Many studies have suggested that a single functional ingredient such as plant extract or organic acid can reduce the dependence on antibiotics and promote the growth and immunity of aquatic animals. In this study, we evaluated the effects of a phytobiotic-based compound additive (Sanacore® GM, SNGM), which had a successful trajectory of commercial application in fish farming. However, its effects on the hepatopancreas health and intestinal microbiota of shrimp after Vibrio challenge have not been well evaluated. In the present study, Pacific white shrimp were fed diets with or without supplementation of SNGM, and the SNGM grades were 0-g/kg (CON), 3-g/kg (SNGM3), and 5-g/kg (SNGM5) diets. The feed trial lasted 60 days, after which a Vibrio parahaemolyticus challenge was performed. The results showed that compared to the CON group, both the SNGM3 and SNGM5 groups had a significantly higher weight gain and a lower feed conversion ratio as well as higher survival after Vibrio parahaemolyticus challenge. In the growth trial, the SNGM3 group had a significantly increased total protein, albumin concentration, and acid phosphatase activity in hemolymph compared to the CON group. In the challenge experiment, the SNGM3 and SNGM5 groups had increased albumin and glucose contents as well as the activities of phenoloxidase, lysozyme, alkaline phosphatase, and superoxide dismutase in hemolymph. Both the SNGM3 and SNGM5 groups had improved morphology of the hepatopancreas and intestine. The SNGM5 group had alleviated gut microbiota dysbiosis induced by Vibrio infection by increasing the potential probiotic bacterium abundance (Shewanella) and decreasing the potential pathogenic bacteria abundance (Vibrio, Photobacteriuma, Pseudoalteromonas, and Candidatus_Bacilloplasma). In conclusion, the dietary phytobiotic-based additive at 3-g/kg level increased the growth and Vibrio parahaemolyticus resistance of Pacific white shrimp by promoting immune-related enzyme activities and improving the morphological structure of the hepatopancreas and intestine and the intestinal microbiota composition.

Yadong trout (Salmo trutta fario) is an important and characteristic aquaculture fish species in Yadong, Xizang, China. Farmed Yadong trout has been produced on a large scale. Usually, two different-colored eggs (yellow and orange) are produced during Yadong trout farming and show differential reproductive performance. There has been very limited information on the nutrient composition of eggs with different colors, and relevant results have only been reported for rainbow trout. The present study aimed to analyze the nutrient compositions in different-colored Yadong trout eggs to elucidate the factors responsible for the different reproductive performances of the two egg types. The experimental samples were collected from Yadong Industry Park, where the broodstocks were reared with artificial compound feeds. Each egg type was analyzed in 3 replicates. Yellow eggs were produced by 2–3 year-old broodstocks, and orange eggs were produced from 3–5 year-old broodstocks. After spawning, the eggs were cryopreserved and transported to the laboratory by plane. The samples were lyophilized and used for the determination of proximate composition, fatty acids, amino acids, and other reproduction-related nutrients. The crude protein and crude lipid contents were analyzed using the Kjeldahl and Soxhlet extraction methods, respectively. The fatty acid composition (expressed as % total fatty acids) and amino acid composition (expressed as % dry matter) were assayed using gas chromatography and an automatic amino acid analyzer, respectively. The protein carbonyl and malondialdehyde concentration were assayed using commercial kits supplied by Nanjing Jiancheng Bioengineering Institute. The α-vitamin E and astaxanthin were assayed using national standard methods, and the α-vitamin E was measured from wet samples. The statistics of proximate composition, fatty acids, and amino acids data were determined using a t-test for independent samples. The results were expressed as mean ± standard error, and showed that yellow eggs had lower contents of crude protein and ash contents, but higher contents of crude lipid and moisture than orange eggs. There was no significant difference in carbohydrate and energy content between yellow and orange eggs. The saturated fatty acid (SFA), n-3 polyunsaturated fatty acid (n-3 PUFA), and docosahexaenoic acid (DHA) contents of yellow eggs were significantly lower than those of orange eggs, while the n-6 polyunsaturated fatty acids (n-6 PUFA) and EPA contents did not differ significantly between the two egg types. The C16:0 and C20:0 contents of yellow eggs were significantly lower than those of orange eggs, while the contents of monounsaturated fatty acids (MUFA), including C16:1n-7, C18:1n-9, C20:1n-9, and C22:1n-9, of yellow eggs were significantly higher than those of orange eggs. The contents of essential amino acids, non-essential amino acids, and total amino acids were slightly lower in yellow eggs compared to orange eggs. Among the essential amino acids, the contents of valine, methionine, leucine, lysine, and histidine in yellow eggs were significantly lower than those in orange eggs. Among the non-essential amino acids, except for glycine and alanine which were significantly lower in yellow eggs than in orange eggs, the contents of other amino acids did not differ significantly between the two egg types. The contents of protein carbonyl and malondialdehyde in yellow eggs were higher than those in orange eggs, while the contents of α-vitamin E and astaxanthin in yellow eggs were lower than those in orange eggs. In conclusion, orange eggs had higher contents of protein, some essential amino acids, DHA, α-vitamin E, and astaxanthin, but lower contents of MUFA, crude lipid, and peroxidation products (protein carbonyl and malondialdehyde) than yellow eggs. These differences in nutrient composition may contribute to the superior reproductive performance of orange eggs over yellow eggs.

The polychaeta Neanthes japonica is a common by-product in mariculture ponds. It is rich in essential nutrients, but has not been well-explored. Therefore, this 56-day experiment investigated the effects of substituting N. japonica meal for dietary fishmeal on juvenile tiger puffer (15.49 ± 0.02 g, n = 450 fish). The control diet (CON) contained 40% fishmeal. Freeze-dried N. japonica meal (FNM) was supplemented into CON at the levels of 3% (FNM3), 6% (FNM6), and 9% (FNM9), replacing fishmeal. The fifth diet contained 6% oven-dried N. japonica meal (ONM6), replacing fishmeal. The results indicated that no significant difference was observed in growth, feed efficiency, and somatic index among all the treatment groups. The feed intake of the FNM6 group was significantly higher compared to CON. No significant difference was detected in fish proximate composition, as well as the fatty acid composition, amino acid composition, and muscle texture. The supplementation of N. japonica meal decreased the activities of intestinal lipase and α-amylase. The addition of freeze-dried N. japonica meal significantly up-regulated the expression of the intestinal amino-glycine transporter pat1. It was concluded that adding 9% N. japonica meal to the feed had no significant effect on the growth performance and body composition of juvenile tiger puffer.

Intermittent and chronic hypoxia are common stresses to marine fish, but the different responses of fish to intermittent and chronic hypoxia have not been well-known. In this study, tiger puffers were farmed in normoxia conditions (NO, 6.5 ± 0.5 mg/L), intermittent hypoxia (IH, 6.5 ± 0.5 mg/L in the day and 3.5 ± 0.5 mg/L in the night), or choric hypoxia (CH, 3.5 ± 0.5 mg/L) conditions for 4 weeks, after which the growth, nutrient metabolism and three hifα isoforms expression were measured. Both intermittent and chronic hypoxia decreased the fish growth and visceral weight but increased the feed conversion ratio and blood hemoglobin content. Chronic hypoxia but not intermittent hypoxia promoted protein synthesis and whole-fish protein content by activating mtor gene expression and promoted the glycolysis pathway by activating gene expression of hif1α and hif2α. Intermittent hypoxia but not chronic hypoxia decreased the hepatic lipid synthesis by inhibiting fasn and srebf1 gene expression. Meanwhile, intermittent hypoxia reduced the monounsaturated fatty acid content but increased the n-3 polyunsaturated fatty acids percentage. The results of this study clarified the adaptive mechanism of tiger puffer to intermittent and chronic hypoxia, which provides important information about mechanisms of hypoxia adaption in fish.

Fish meal and fish oil are important sources of protein and lipid in feeds. The lack of fish meal and fish oil supply has become an important limiting factor for the aquaculture industry. The proportion of fish oil and fish meal used in commercial feeds for farmed fish and crustaceans is continually decreasing, while the carbohydrate content is increasing. Carbohydrates are one of the three major nutrients that provide energy for the body. They have a much lower production price than protein and fat. Starch is a polymeric carbohydrate made from glucose molecules; it is the most commonly used in aquatic feeds and can replace fish meal and fish oil to reduce feed cost. Therefore, it is important to fully explore the nutritional function of carbohydrates for aquaculture. Hypoxia is a common stress in aquaculture, and acute hypoxia may lead to massive mortality of cultured fish in a short period of time resulting in serious economic losses to aquaculture. Therefore, it is crucial to find ways to improve the acute hypoxia tolerance of fish. Fish mainly use glucose for energy under acute hypoxia. Hypoxia inhibits oxidative phosphorylation in mitochondria and activates the anaerobic glycolysis pathway. Glucose degrades to produce lactate and ATP. Carnivorous fishes have limited absorption and utilization capacities to feed carbohydrates, unlike omnivorous fishes. Dextrin is an intermediate starch hydrolysis product, with a molecular weight between starch and glucose; it has good adhesion properties and is more easily digested and absorbed than starch. Therefore, we hypothesized that the use of easily digestible carbohydrate in the feed is an effective way to improve the acute hypoxia tolerance of fish. Takifugu rubripes is loved by Japanese and Korean consumers owing to its delicious taste and high nutritional value. It is a characteristic species of Chinese mariculture fish. It is mainly cultured in a high-density factory, and the dissolved oxygen in the water often relies on water exchange and an oxygenation pump; its gill cover is degraded and is at risk of acute hypoxia. This study determined the effect of the addition of corn starch or dextrin (corn starch hydrolysate) to the feed on growth performance, acute hypoxia survival rate, metabolite content, and the hypoxia inducible factor (HIF) signaling pathway of T. rubripes after 8 weeks of feeding. There were no significant differences in weight gain, feed conversion ratio, hepatosomatic index, viscerosomatic index, condition factor, and body composition between the starch group and the dextrin group (P > 0.05). However, the survival rate during acute hypoxia of the dextrin group was significantly higher than that of the starch group (P < 0.05). There were no significant differences in the liver glycogen and lactate contents, and lactate dehydrogenase A4 (ldha) gene expression between the starch group and dextrin group (P > 0.05) during normoxia. However, the lactate content and ldha gene expression were significantly higher in the liver of the dextrin group than those in the starch group (P < 0.05) during hypoxia. This indicated that feeding dextrin strongly activated anaerobic glycolysis to provide more energy under hypoxia. The serum triglyceride (TG) content significantly increased in the dextrin group compared with the normoxia groups, although the TG content in the serum and liver significantly decreased in the starch group after acute hypoxia (P < 0.05). This suggested that feeding starch promoted lipid catabolism and oxygen consumption. There was no significant difference in the total soluble protein content of the muscle between the starch group and the dextrin group (P > 0.05) during normoxia. However, the total soluble protein content of the muscle decreased in the dextrin group compared with the starch group (P < 0.05) after acute hypoxia. Meanwhile, the total muscle soluble protein content, and the gene expression of liver v-akt murine thymoma viral oncogene homolog 1 (akt1), and mechanistic target of rapamycin kinase (mtor) significantly decreased in the dextrin group after hypoxia compared with the normoxia group. However, the liver mtor gene expression significantly increased in the starch group after hypoxia (P < 0.05). This data demonstrated that protein synthesis was inhibited in the dextrin group under hypoxia. Hypoxia inducible factor (HIF) is the most critical transcription factor in cellular response to hypoxic stress. The dextrin group had higher hypoxia inducible factor 1 subunit alpha like (hif-3α) gene expression in the liver and lower hypoxia inducible factor 1 subunit alpha a (hif-1α) gene expression in the muscle (P < 0.05) compared with the starch group during normoxia. The gene expression of liver hif-1α and hif-3α and muscle hif-1α and vascular endothelial growth factor A (vegfa) significantly increased in the dextrin group compared with the starch group (P < 0.05) during hypoxia. This proved that feeding dextrin strongly activated the HIF signaling pathway under hypoxia. In summary, replacing starch with easily digestible dextrin in the feed did not affect the growth performance. Instead, it activated the HIF signaling pathway and anaerobic glycolysis to provide more energy for fish. Meanwhile, feeding dextrin inhibited lipid catabolism and protein synthesis, and reduced oxygen consumption to improve the acute hypoxia tolerance of T. rubripes. The study provides important guidance for the formulation design of hypoxia-tolerant feed and healthy development of aquaculture.

Fish are the main source of long-chain polyunsaturated fatty acids (LC-PUFA), in particular docosahexaenoic acid (DHA, 22:6n-3) and eicosapentaenoic acid (EPA, 20:5n-3), which are nutritionally valuable to humans. Moreover, lipid and fatty acid distribution in fish tissues are highly diverse across species. The lipid distribution pattern across tissues determines fatty acid profile, one of the product quality indicators of fish. However, this diversity of lipid distribution and fatty acid profile is not fully known, although several studies have been conducted to compare the nutritive composition of muscle in different fish species in both freshwater and marine environments. This study aimed to comprehensively investigate the lipid distribution and fatty acid profile, as well as the somatic indexes and approximate composition of five benthic marine fish species, namely yellow anglerfish (Lophius litulon), flathead (Platycephalus indicus), eelpout (Zoarces viviparus), East Asian flatfish (Pleuronichthys cornutus), and zebra sole (Zebrias zebrinus). Fishes were purchased from the 15th Street Seafood Market of Qingdao, which were stored on ice since captured in an inshore fishery in Qingdao (located at 119°30'–121°00'E and 35°35'–37°09'N), and then delivered to the market from the fishing harbor in the same morning. After purchase, fishes were kept on ice and immediately taken to the laboratory. The experimental design consisted of nine fish of each species bulked in groups of three, comprising three replicates. First, the total weight and length of each fish were measured, and the liver and viscera weight were recorded to calculate the viscerosomatic index (VSI), hepatosomatic index (HSI), and condition factor (CF). Subsequently, samples of muscle, liver, brain, eye, skin, subcutaneous adipose tissue around fins (only for East Asian flatfish and zebra sole), and intraperitoneal adipose tissue (only for flathead) were collected for lipid and fatty acid analysis. The dorsal muscle sampling position is behind the head on the right body side. The ventral muscle samples were collected under the dorsal muscle sampling spot. The proximate composition analysis of the dorsal muscle, ventral muscle, and liver (three individual samples per group) was performed according to the Association of Official Analytical Chemists standard methods. For the moisture assay, samples were oven-dried at 105 ℃ until they achieved a constant weight. The protein content was assayed by measuring nitrogen (N × 6.25) using the Soxhlet method, the lipids were analyzed using the Soxhlet method (petroleum ether extraction), and the ash by incineration at 550 ℃. The fatty acid compositions of all tissues were analyzed with gas chromatography (GC-2010, Shimadzu, Japan). The results showed that the flat body type of flatfish determines that the gut in these fish species cannot store high lipid contents in the liver or intraperitoneal adipose tissues. Like other flatfish, East Asian flatfish and zebra sole had lower HSI and VSI. In contrast, the HSI and VSI of yellow anglerfish and flathead were associated with high lipid contents in the gut. Additionally, the lipid distribution across tissues indicated that yellow anglerfish and flathead predominantly stored lipid in the liver and intraperitoneal adipose tissue, respectively. The muscle lipid content of all the five species was low, especially for yellow anglerfish and zebra sole (0.3%–0.4%). Yellow anglerfish, flathead, and East Asian flatfish had higher liver lipid content (19%–29%) than zebra sole and eelpout (4%–5%). Yellow anglerfish and flathead store lipid predominantly in the liver and intraperitoneal adipose tissue, respectively. The n-3 LC-PUFA content, especially DHA, in the muscle of yellow anglerfish was significantly higher than that of other species. The yellow anglerfish dorsal muscle also had the highest 18:1n-9 content. The relative abundances of different monounsaturated fatty acids (MUFA) and saturated fatty acids (SFA) in different fish species indicate a preference for energy storage and lipid mobilization. The most distinct fatty acid characteristics of the dorsal muscle of eelpout were low 16:0 content and high EPA content. For liver fatty acids, flathead and East Asian flatfish had significantly high MUFA contents, such as 18:1n-9, but their DHA contents were low. High DHA, 20:4n-6, and 22:5n-3 contents were consistently observed in nearly all yellow anglerfish, eelpout, and East Asian flatfish tissues, respectively, while low EPA content was observed for all of them. Among all five fish species, eelpout had a much higher ARA content than the other species in nearly all tissues. This could be due to the high ARA level in the food sources, namely algae. Yellow anglerfish had significantly high n-3 LC-PUFA content and thus high fatty acids nutritional value. This study revealed that even though these fishes are all benthic species, there are great differences in lipid and fatty acid composition among them.

Palm oil, with its higher production, lower prices, and higher levels of palmitic acid and oleic acid, may have great potential for use in the aquafeed industry. In this study, with an 8-week feeding experiment, the efficacy of palm oil as a substitute for fish oil in tiger puffer feeds was comprehensively evaluated. The control diets (FO group) contained 8% marine fish oil as the main lipid source, while in the treatment diets, the added marine fish oil was replaced with palm oil at 25%, 50%, 75%, and 100%, respectively, which was named 25PO, 50PO, 75PO, and 100PO, respectively. Juvenile tiger puffers with an initial weight of 15.0 ± 0.04 g were used, with three replicate tanks of 30 juvenile fish tiger puffer for each dietary group. The fish oil replacement by palm oil did not have an adverse effect on fish growth and feeding, but the weight gain decreased by 17.3% in group PO100. Palm oil had no significant effects on fish proximate composition and muscle texture. The effects of dietary palm oil on muscle fatty acid composition were not significant, with DHA and EPA significantly lowered only in the 100PO group. In contrast, the changes in liver and intestinal fatty acid compositions in response to diets were more significant than those in the muscle. In the intestine, the replacement of more than 50% fish oil by palm oil significantly downregulated the gene expression associated with peroxisomal fatty acid β-oxidation and triglyceride hydrolysis, while upregulated the expression of cholesterol biosynthetic genes. In the liver, the replacement of more than 75% fish oil also significantly upregulated the cholesterol synthesis. In conclusion, palm oil can replace 75% of added marine fish oil in tiger puffer diets and does not adversely affect the growth performance, feed utilization, muscle composition, and muscle texture.

This study aimed to evaluate the effects of combined replacement of fishmeal (FM) and fish oil (FO) with poultry byproduct meal (PBM) and mixed oil (MO, poultry oil: coconut oil = 1 : 1) on growth performance, body composition and muscle quality of tiger puffer (Takifugu rubripes). Fish with an average initial body weight of 14.29 g were selected for the feeding experiment. FM accounting for 0%, 5%, and 10% of the diet was replaced by PBM. For each grade of FM replacement, 5% FO or MO was used as added oil. The six experimental diets were designated as FO-FM, MO-FM, FO-5PBM, MO-5PBM, FO-10PBM, and MO-10PBM, respectively. Each treatment was performed in triplicate with 30 fish per replicate. The feeding period was 45 days. There was no significant difference in growth performance among the groups. Dietary supplementation of both PBM and MO had marginal effects on whole-fish proximate composition, except that dietary MO supplementation significantly increased the liver moisture content. In serum, there were no significant differences in contents of triglyceride, total cholesterol, total bile acid, and protein carbonyl among groups, but the malondialdehyde content was reduced by MO. The fatty acid composition in fish mirrored those in the diets, but the omega-3 sparing effects of saturated and monounsaturated fatty acid in MO can still be observed. Dietary PBM and MO had marginal effects on free amino acid composition and texture of fish muscle, but exerted complicated effects on the muscle volatile flavor compound composition. In conclusion, combined fishmeal (10% of the diet) and fish oil (5% of the diet) replacement with poultry byproduct and mixed oil (poultry oil + coconut oil) had no adverse effects on the growth performance and body proximate composition of farmed tiger puffer. However, these replacements changed the muscle flavor compound profile.

Carbohydrates are a common and economical energy source in animal feeds. However, most fish show a persistent postprandial hyperglycemia after intake of a high-carbohydrate diet. Unfortunately, the mechanism of glucose metabolism in fish is still unclear. In the present study, tiger puffer (Takifugu rubripes) and turbot (Scophthalmus maximus) were intraperitoneally injected or orally administered with glucose or fructose (500 mg/kg body weight) to evaluate the ability of fish to utilize carbohydrates. Afterwards, serum glucose, fructose, pyruvate, insulin levels, and acute hypoxia tolerance were measured. Our results showed increased serum glucose level and then decreased post intraperitoneal injection with glucose, and reached a peak after 0.5 hours in turbot and 1 hour in tiger puffer. Tiger puffer had significantly lower liver glycogen, serum glucose, fructose, pyruvate, and insulin contents than turbot. Glucose and fructose only induced insulin secretion in turbot, but did not change serum insulin level in tiger puffer. Glucose was a stronger stimulator of insulin than fructose in the two marine species. Both intraperitoneal injection and oral fructose intake increased serum glucose level, while intraperitoneal or oral glucose also increased serum fructose level. Intraperitoneal injection of glucose promoted absorption and utilization of glucose in the blood more effectively than oral glucose intake. In addition, turbot and tiger puffer were intolerant to acute hypoxia, whereas supplementation with glucose or fructose improved hypoxia tolerance in the two marine fishes by activating anaerobic glycolysis. Taken together, our results provide important scientific information for understanding the mechanism for glucose and fructose utilization and improving hypoxia tolerance in fish.

Yadong trout (Salmo trutta fario), the only salmonid fish in the Tibetan Plateau, is a national agricultural product with geographical indications in Yadong. The development of Yadong trout aquaculture has significant implications for local farmers. However, no study has yet investigated the nutrient requirements of this fish. This study aimed to analyze the proximate amino acid, and fatty acid composition of various tissues of wild and farmed Yadong trout, in order to provide a reference for the evaluation of fish fillets and the formulation of optimal feed. Ten wild fish captured in the Yadong River, and 10 fish farmed with formulated feed in Yadong Industry Park were used in this study. The farmed fish were F1 generation wild broodstock captured in the Yadong River and fed formulated feeds throughout their lifetime. The body length of wild Yadong trout was in the range of 13.4~28.7 cm, and the body weight was in the range of 38.48~346.85 g. The body length and body weight of farmed Yadong trout were in the range of 16.4~24.5 cm and 78.39~275.29 g, respectively. Frozen samples were transported to the laboratory by flight. The proximate composition of whole fish, muscle, and liver; fatty acid composition of whole fish and various tissues including muscle, liver, intestine, brain, and eye; as well as amino acid composition of whole fish, muscle, and liver were analyzed. The fatty acid composition (expressed as % total fatty acids) and amino acid composition (expressed as % dry matter basis) were assayed using gas chromatography and an automatic amino acid analyzer, respectively. In addition, t-tests were performed for independent samples; results are expressed as the mean ± standard deviation. The results showed that wild fish had lower condition factors but higher moisture and ash content than farmed fish. Wild fish muscle had lower crude lipid content but higher moisture content than farmed fish. The whole-body protein and lipid contents, as well as the proximate composition of the liver, were not significantly different between wild and farmed fish (P > 0.05). The contents of saturated fatty acids (mainly C16:0 and C18:0) and n-3 polyunsaturated fatty acid (PUFA) in whole fish, muscle, and liver were significantly higher (P < 0.05), whereas contents of monounsaturated fatty acids (MUFA) (mainly C16:1n-7 and C18:1n-9) and n-6 PUFA (mainly C18:2n-6) were significantly lower in wild Yadong trout than in farmed Yadong trout (P < 0.05). EPA and C20:4n-6 in whole fish, muscle, and liver, as well as DHA in the muscle of wild Yadong trout were significantly higher than those in farmed Yadong trout (P < 0.05). In the intestine of wild Yadong trout, the contents of C14:0, C16:0, C18:0, C16:1n-7, C20:5n-3, and C22:5n-3 were significantly higher (P < 0.05), while those of C18:1n-9 and C18:2n-6 were significantly lower (P < 0.05) than in the farmed fish. In the brain of wild Yadong trout, the contents of C16:1n-7, C20:5n-3, and C22:5n-3 were significantly higher (P < 0.05), while the contents of C18:1n-9 and C20:2n-6 were significantly lower (P < 0.05) than those of farmed fish. In the eyes of wild Yadong trout, the contents of C14:0, C16:0, and C18:0, C16:1n-7, C20:1n-9, C20:2n-6, C20:4n-6, C20:5n-3, and C22:5n-3 were significantly higher (P < 0.05), while the contents of C18:1n-9, C22:1n-9, C24:1n-9, C18:2n-6, and C18:3n-3 were significantly lower (P < 0.05) than those of farmed Yadong trout. The total essential amino acid content in wild fish was significantly higher than that in farmed fish. The contents of threonine, valine, phenylalanine, lysine, and glycine in the muscle of wild fish were significantly higher (P < 0.05) than those in farmed fish, while no significant difference (P > 0.05) was observed in other amino acids. These results indicate that wild Yadong trout were leaner than farmed trout in terms of muscle lipid content. For trout, which are mainly consumed fresh, this trait may make farmed Yadong trout more acceptable than wild trout. However, in terms of fatty acid composition and amino acids, the wild Yadong trout seemed to be more acceptable than farmed trout. In particular, n-3 PUFA content is an important nutritional trait in fish fillets. The wild Yadong trout had higher n-3 PUFA contents than the farmed trout. Thus, the fish oil in the feeds of Yadong trout should not be omitted, considering that fish chemical composition generally reflects that of their diets. In addition, the price of alternative oils such as soybean oil is no longer low; the use of lipid sources in the diets of Yadong trout should be reviewed. Similarly, the essential amino acid content in wild Yadong trout was higher than that in the farmed trout, suggesting that the protein sources should be reviewed, and a certain level of fish meal should be guaranteed. In conclusion, the results of this study indicate that the formulated feeds of Yadong trout need to be further optimized.

Astaxanthin (AST), functioning as an efficient antioxidant and pigment, is one of the most expensive additives in shrimp feeds. How to improve the uptake efficiency of dietary astaxanthin into farmed shrimp is of significance. The present study investigated the effects of lysophosphatidylcholine (LPC), an emulsifier, on dietary astaxanthin efficiency, growth performance, body color, body composition, as well as lipid metabolism of juvenile Pacific white shrimp (average initial body weight: 2.4 g). Three diets were prepared: control group, the AST group (supplemented with 0.02% AST), and the AST + LPC group (supplemented with 0.02% AST and 0.1% LPC). Each diet was fed to triplicate tanks, and each tank was stocked with 30 shrimp. The shrimp were fed four times daily for eight weeks. The AST supplementation improved the growth of white shrimp, while LPC further promoted the final weight of shrimp, but the whole-shrimp proximate composition and fatty acid composition were only slightly affected by AST and LPC. The LPC supplementation significantly increased the astaxanthin deposition in the muscle. The LPC supplementation significantly increased the shell yellowness of both raw and cooked shrimp compared to the AST group. Moreover, the dietary LPC increased the high-density lipoprotein-cholesterol content but decreased the low-density lipoprotein-cholesterol content in the serum, indicating the possible regulation of lipid and cholesterol transport. The addition of astaxanthin significantly up-regulated the expression of npc2 in the hepatopancreas compared to the control group, while the addition of LPC down-regulated the expression of mttp compared to the AST group. In conclusion, the LPC supplementation could facilitate the deposition of dietary astaxanthin into farmed shrimp and further enlarge the beneficial effects of dietary astaxanthin. LPC may also independently regulate shrimp body color and cholesterol transportation. This was the first investigation of the promoting effects of LPC on dietary astaxanthin efficiency.

Lard (LD) and Basa fish offal oil (BFO) have similar fatty acid profiles, both containing high contents of saturated fatty acids (SFA) and monounsaturated fatty acids (MUFA). The present study aimed to investigate the efficacy of partial or complete replacement of marine fish oil (MFO, herring oil) by LD or BFO in the diets of tiger puffer. The control diet contained 49.1% crude protein and 9.28% crude lipid content including 6% added MFO. In other diets, 1/3, 2/3, and 3/3 of the added MFO was replaced by LD or BFO, respectively. Each diet was fed to triplicate tanks of juvenile fish (initial body weight, 13.88 g). A 46-day feeding trial was conducted in a flow-through seawater system. Each diet was fed to triplicate 200-L rectangular polyethylene tanks, each of which was stocked with 30 fish. Fish were fed to satiation three times a day. The complete replacement of added MFO (replacing 65% of the total crude lipid) had no adverse effects on fish growth performance in terms of survival (>94%), weight gain (360–398%), feed intake (2.37–3.04%), feed conversion ratio (0.84–1.02), and somatic indices. The dietary LD or BFO supplementation also had marginal effects on fish body proximate composition, biochemical parameters, muscle texture, and water-holding ability, as well as the hepatic expression of lipid metabolism-related genes. Partial (2/3) replacement of added MFO by LD or BFO did not significantly reduce the muscle n-3 LC-PUFA content, indicating the n-3 LC-PUFA sparing effects of SFA and MUFA in LD and BFO. In general, dietary LD or BFO reduced the peroxidation level and led to significant changes in the muscle volatile flavor compound profile, which were probably attributed to the change in fatty acid composition. The results of this study evidenced that LD and BFO are good potential lipid sources for tiger puffer feeds.

A feeding trial was conducted to evaluate the biological activities of Enteromorpha prolifera bio-products in the diets of Pacific white shrimp (Litopenaeus vannamei). Bio-products of E. prolifera included E. prolifera meal, E. prolifera hydrolysate and E. prolifera polysaccharide, which was supplied using different processing procedures. The control diet was supplemented without any E. prolifera bio-products or dietary attractants. Experimental diets were formulated to contain 0.2% and 0.4% of E. prolifera hydrolysate (EPH0.2% and EPH0.4%), 0.03% of E. prolifera polysaccharide (EPP0.03%), 3% of E. prolifera meal (EPM3%), 0.1% of dimethyl-β-propiothetn (DMPT0.1%) and 1% of squid paste (SP1%). Shrimp (~8 g) were randomly distributed in 21 tanks and fed for 44 days. Feed intake showed that 3% of E. prolifera meal and 0.4% of E. prolifera hydrolysate in diets exhibited similar attractant effects as 0.1% of DMPT. Gross qualitative observation showed that the abundance of lipid droplets decreased in hepatopancreas of the EPH0.4% and EPM3% groups, which were supported by hepatopancreas triacylglycerol (TG), where significantly lower concentrations were observed in the EPH0.4% and EPM3% groups compared with the control group. Similarly, TG and low-density lipoprotein cholesterol in serum significantly decreased in the EPH0.4%, EPP0.03% and EPM3% groups compared to the control group. Supplemental E. prolifera bio-products resulted in significantly higher serum glutathione level of EPP0.03% or superoxide dismutase activities of EPH0.4% and EPM3%, but significantly lower serum malondialdehyde level of EPM3%. In addition, tnf-α expression in hepatopancreas was significantly down-regulated in shrimp fed the EPH0.2%, EPH0.4% and EPM3% diets. Based on survival analysis, E. prolifera bio-products improved the resistance of shrimp to hypoxic stresses. Thus, this study confirmed that bio-products of E. prolifera supplied using different processing procedures could be used to reduce the amount of E. prolifera in feed of shrimp without compromising their biological functions.

The aim of this study was to investigate the effects of imbalanced dietary BCAAs, especially Leu, on the growth and BCAA metabolism in turbot. A control diet was formulated by keeping optimum levels of Leu, Ile and Val. Four experimental diets were prepared by removing supplemental crystalline Leu (deficiency) or supplementing double the amount of Leu, Ile or Val (excess) in the control diet. The growth was not significantly decreased by an excess of Leu, Ile or Val. Fish fed an excess of any particular BCAA significantly increased its postprandial (2 and 6 h) concentration in the plasma, muscles, and liver, but did not decrease the other two BCAA concentrations. The expression of intestinal b0at1 was down-regulated by excessive dietary Leu, Ile or Val. For BCAA catabolism, the mRNA levels of bcat2 in the muscles as well as bckdha and bckdhb in the livers of the Leu-deficient group were the lowest among all the groups, but were up-regulated by excess dietary Leu, Ile or Val. In conclusion, in terms of growth, turbot had high plasticity to an excess of any particular BCAA. Meanwhile, the antagonistic effect caused by an excess of one BCAA were reflected in intestinal amino acid absorption and BCAA catabolism.

A 12-week feeding experiment was conducted to evaluate the effects of replacing fish oil (FO) with beef tallow (BT) on the fatty acid composition of farmed tiger puffer (Takifugu rubripes). Two replacement strategies were used: a standard Graded Dietary Replacement of FO with BT (GDR strategy) and Alternate Feeding between FO- and BT-based Diets (AFD strategy). The positive and negative control diets were formulated with 6% FO (FO-C group) or BT (BT-C group) as the sole added lipid source. In the GDR strategy, three experimental diets were formulated, with 25, 50 and 75% of the added FO in the FO-C diet replaced with BT, named 25BT, 50BT and 75BT, respectively. In the AFD strategy, alternated feeding patterns between the FO-C and BT-C diet—namely, 1, 2 and 3 weeks with BT-C followed by 1 week feeding with FO-C (1BT-1FO, 2BT-1FO and 3BT-1FO, respectively)—were applied. Each diet or feeding strategy was assigned to triplicate tanks. The results showed that dietary BT inclusion reduced the contents of long-chain polyunsaturated fatty acids (LC-PUFA) in both the muscle and liver (edible tissues for this species) of the experimental fish, and the liver displayed a more drastic decrease than the muscle. The LC-PUFA content linearly decreased with the decreasing dietary FO levels in the GDR strategy. However, in the AFD strategy, a linear relationship was not observed between the LC-PUFA content and the FO feeding duration. The 3BT-1FO treatment resulted in higher LC-PUFA content than 2BT-1FO. When comparing the two strategies with the same final FO administration level—namely, 50BT vs. 1BT-1FO, and in particular, 75BT vs. 3BT-1FO—the AFD strategy resulted in higher LC-PUFA contents in both the muscle and liver than the GDR strategy. In conclusion, when FO was replaced with BT in the diets, alternate feeding between FO- and BT-based diets resulted in a higher LC-PUFA content than the standard direct replacement. Three weeks of feeding with BT-C followed by one week of feeding with FO-C appeared to be a good alternate feeding pattern. This study provided a promising strategy of FO-sparing in fish farming when the LC-PUFA contents were maintained as high as possible.

The fatty acid accumulation in fish tissues are closely related to fish sex, yet the sex differences in fish fatty acids have not been fully known. This experiment investigated the sex differences in fatty acid composition of Chinese tongue sole (Cynoglossus semilaevis), which have typical sexual dimorphism and reversal. Three sexes, namely females, males and pseudomales, were involved in this study. Five batches of fish samples were collected from different fish farms in Shandong Province, China. These fish were identified to be at the gonadal development stage of III–IV. The disparity of fatty acid between sexes (female vs male and pseudomale vs. male) was evaluated by the distance coefficient (Dsex) and multi-variate similarity of percentages analysis (SIMPER). The highest Dsex values between females and males were found in gonad, followed by liver and eye. The fatty acids that differed between females and males were mainly DHA, 16:1n-7, 18:1n-9, and 18:0. The sex difference in DHA and 18:1n-9 contributed significantly to the overall sex difference in fatty acid of brain, eye, and gonad, whereas that in 16:1n-7 contributed significantly in heart, gill, liver, and muscle. The sex difference in 18:0 contributed significantly to the overall sex difference in fatty acid of heart, gill, gut, and skin. The sex differences in fatty acid between pseudomales and males were generally insignificant. In conclusion, at this gonadal development stage (III–IV), the sex differences in fatty acid between female and male Chinese tongue sole have emerged, mainly in the gonad. The testes had higher DHA levels but lower levels of 16:1n-7 and 18:1n-9 than ovaries. In addition, for pseudomales, the phenotypic sex more substantially determined the fatty acid composition than the genetic sex.

The objective of this study was to investigate the potential effect of graded levels of tryptophan on the growth, cannibalism, and 5-hydroxytryptpamine (5-TH) metabolism in pufferfish (Takifugu obscurus ♀ × Takifugu rubripes ♂). A 63-day feeding trial was performed wherein pufferfish were fed four diets. Three experimental diets were formulated with various levels of tryptophan based on the control diet. Four diets were named as T1, T2, T3, and T4, corresponding to 4.30, 7.80, 14.90, and 23.70 g kg−1 tryptophan of dry diet. Final body weight, weight gain, and specific growth rate were similar between the T1 and T4 groups, but exhibited a significantly increased trend compared to the T2 group. Although survival rate was not affected by various levels of dietary tryptophan, intraspecific cannibalism was significantly reduced in the group fed with highest level of tryptophan (T4). For free amino acid in brain, the concentration of tryptophan was the highest in the T3 group and the lowest in the T2 group, while phenylalanine, tyrosine, and methionine showed an opposite trend between those two groups. The levels of dietary tryptophan not only affected the expression of aromatic amino acid transporter TAT1, but also affected the expression of B0AT1, B0AT2, and 4F2hc in intestine, as well as B0AT1, y+LAT1, and LAT2 in brain. The activity of tryptophan hydroxylase (TPH) in serum increased with the increase of dietary tryptophan, and the expression of TPH1 in brain upregulated in the excessive tryptophan groups (T2, T3, and T4). MAO activity in serum as well as its gene expression in brain and intestine showed a decreased trend in the T4 group. In conclusion, excessive tryptophan (23.70 g kg−1 of dry diet, corresponding to 50.3 g kg−1 of dietary protein) in feed could mitigate cannibalistic behavior of pufferfish and promote the growth, and the reason for this effect might affect the metabolism of 5-TH in vivo.

Cholesterol has been used as additive in fish feeds due to the reduced use of fish meal and fish oil. In order to evaluate the effects of dietary cholesterol supplementation (D-CHO-S) on fish physiology, a liver transcriptome analysis was performed following a feeding experiment on turbot and tiger puffer with different levels of dietary cholesterol. The control diet contained 30% fish meal (0% fish oil) without cholesterol supplementation, while the treatment diet was supplemented with 1.0% cholesterol (CHO-1.0). A total of 722 and 581 differentially expressed genes (DEG) between the dietary groups were observed in turbot and tiger puffer, respectively. These DEG were primarily enriched in signaling pathways related to steroid synthesis and lipid metabolism. In general, D-CHO-S downregulated the steroid synthesis in both turbot and tiger puffer. Msmo1, lss, dhcr24, and nsdhl might play key roles in the steroid synthesis in these two fish species. Gene expressions related to cholesterol transport (npc1l1, abca1, abcg1, abcg2, abcg5, abcg8, abcb11a, and abcb11b) in the liver and intestine were also extensively investigated by qRT-PCR. However, the results suggest that D-CHO-S rarely affected the cholesterol transport in both species. The protein-protein interaction (PPI) network constructed on steroid biosynthesis-related DEG showed that in turbot, Msmo1, Lss, Nsdhl, Ebp, Hsd17b7, Fdft1, and Dhcr7 had high intermediary centrality in the dietary regulation of steroid synthesis. In conclusion, in both turbot and tiger puffer, the supplementation of dietary cholesterol inhibits the steroid metabolism but does not affect the cholesterol transport.

Exogenous cholesterol has been supplemented into aqua-feeds due to the reduced proportions of fishmeal and fish oil. This study aimed to investigate the effects of dietary cholesterol supplementation on the muscle lipidomics of two marine fish species, turbot and tiger puffer. A 70-day feeding trial was conducted, where two low-fishmeal diets supplemented with 0 or 1% cholesterol were used. The lipidomic analysis with targeted tandem mass spectrometry showed that, in turbot, a total of 49 individual lipids exhibited significant differences in their abundance in response to dietary cholesterol, whereas the number was 30 for tiger puffer. Dietary cholesterol up-regulated the abundance of cholesterol and cholesterol ester in both species. In turbot, the dietary cholesterol also increased the abundance of triacylglycerol and acylcarnitine, whereas in tiger puffer, it primarily regulated the abundance of phospholipids and BMP. This was the first time the responses of marine fish muscle lipidomics to dietary cholesterol supplementation have been investigated.

Starvation is a natural process in the life cycle of wild fish, and also a means of body composition regulation for farmed fish. This study with tiger puffer was aimed at investigating the effects of starvation on lipid and fatty acid compositions in fish with different levels of lipid accumulation. Different lipid accumulation levels in tiger puffer were obtained by manipulating the dietary lipid content (8%, 12%, and 16%) in a previous feeding period for 9 weeks. Each diet was fed to sextuplicate net cages in this feeding trial. At the end of the feeding trial, fish with an average initial body weight of 68.26 g were then subjected to starvation for 31 days. Tissue samples were collected at the end of the feeding trial and at 1, 4, 9, 16, and 31 days after starvation. The results showed that the muscle lipid content decreased linearly with starvation time, but the liver lipid content increased firstly (1–16 days of starvation), and thereafter sharply declined. However, no interaction between starvation time and dietary lipid level was observed in the effects on liver and muscle lipid composition. Starvation had slight effects on muscle and liver fatty acid compositions, except that it largely increased the C22:5n-3 content in the muscle. Starvation primarily mobilized C14:0, C16:1n-7, C20:1n-9 and C22:1n-9 in the muscle, and C18:0, C18:1n-9, and EPA in the liver. Interactive effects between starvation time and dietary lipid level were observed for many fatty acids. Short-term (1–4 days) starvation increased the muscle texture parameters, but longer-term starvation decreased them. In conclusion, starvation exerts significant effects on lipid and fatty acid composition in farmed tiger puffer. Customed lipid and fatty acid composition, and possibly customed fillet quality could be obtained through manipulation of starvation time and dietary lipid level in the previous feeding period.

Lysophosphatidylcholine (LPC) has been widely used as emulsifier in animal feeds to enhance the lipid utilization. However, the effects of LPC on fillet quality has rarely been known. The present study was the first time to investigate the response of fish muscle lipidomics to dietary LPC supplementation. Turbot muscle samples were collected after a 56-day feeding trial where the experimental diet contained 0 or 0.25% LPC. Targeted tandem mass spectrometry was used in the lipidomic analysis. A total of 62 individual lipids (58 up-regulated and 7 down-regulated by LPC) showed significant difference in concentration in response to dietary LPC. Most of these differentially abundant lipids were diacylglycerol, free fatty acid and cardiolipin, and they all were up-regulated by dietary LPC. However, LPC exerted only marginal effects on muscle fatty acid composition and lipid content. The effects of dietary LPC on fillet lipid composition cannot be neglected in fish product evaluation.

A nine-week feeding trial was conducted to investigate changes in the intestinal microbiota of turbot in response to alternate feeding between terrestrially sourced oil (TSO)- and fish oil (FO)-based diets. The following three feeding strategies were designed: (1) continuous feeding with the FO-based diet (FO group); (2) weekly alternate feeding between soybean oil (SO)- and FO-based diets (SO/FO group); and (3) weekly alternate feeding between beef tallow (BT)- and FO-based diets (BT/FO group). An intestinal bacterial community analysis showed that alternate feeding reshaped the intestinal microbial composition. Higher species richness and diversity of the intestinal microbiota were observed in the alternate-feeding groups. A PCoA analysis showed that the samples clustered separately according to the feeding strategy, and among the three groups, the SO/FO group clustered relatively closer to the BT/FO group. The alternate feeding significantly decreased the abundance of Mycoplasma and selectively enriched specific microorganisms, including short-chain fatty acid (SCFA)-producing bacteria, digestive bacteria (Corynebacterium and Sphingomonas), and several potential pathogens (Desulfovibrio and Mycobacterium). Alternate feeding may maintain the intestinal microbiota balance by improving the connectivity of the ecological network and increasing the competitive interactions within the ecological network. The alternate feeding significantly upregulated the KEGG pathways of fatty acid and lipid metabolism, glycan biosynthesis, and amino acid metabolism in the intestinal microbiota. Meanwhile, the upregulation of the KEGG pathway of lipopolysaccharide biosynthesis indicates a potential risk for intestinal health. In conclusion, short-term alternate feeding between dietary lipid sources reshapes the intestinal microecology of the juvenile turbot, possibly resulting in both positive and negative effects.

Booming fish farming results in a relative shortage of fish oil (FO) supply, meaning that alternative oils are increasingly used in fish feeds, which leads to reduction of long-chain polyunsaturated fatty acids (LC-PUFAs) and other relevant changes in fish products. This study investigated the efficacy of an FO-finishing strategy in recovering the muscle quality of farmed tiger puffer. An eight-week feeding trial (growing-out period) was conducted with five experimental diets, in which graded levels (0 (control), 25, 50, 75, and 100%) of added FO were replaced by poultry oil (PO). Following the growing-out period was a four-week FO-finishing period, during which fish in all groups were fed the control diet. Dietary PO significantly decreased the muscle LC-PUFA content, whereas in general, the FO-finishing strategy recovered it to a level comparable with that of the group fed FO continuously. The recovery efficiency of EPA was higher than that of DHA. Dietary PO also led to changes of volatile flavor compounds in the muscle, such as butanol, pentenal, and hexenal, whereas the FO-finishing strategy mitigated the changes. In conclusion, the FO-finishing strategy is promising in recovering the LC-PUFA and volatile-flavor-compound composition in farmed tiger puffer after the feeding of PO-based diets.

Booming fish farming results in relative shortage of fish oil (FO), making it urgent to explore alternative lipid sources. This study comprehensively investigated the efficacy of FO replacement with poultry oil (PO) in diets of tiger puffer (average initial body weight, 12.28 g). An 8-week feeding trial was conducted with experimental diets, in which graded levels (0, 25, 50, 75, and 100%, named FO-C, 25PO, 50PO, 75PO, and 100PO, respectively) of FO were replaced with PO. The feeding trial was conducted in a flow-through seawater system. Each diet was fed to triplicate tanks. The results showed that FO replacement with PO did not significantly affect the growth performance of tiger puffer. FO replacement with PO at 50-100% even slightly increased the growth. PO feeding also had marginal effects on fish body composition, except that it increased the liver moisture content. Dietary PO tended to decrease the serum cholesterol and malondialdehyde content but increase the bile acid content. Increasing levels of dietary PO linearly upregulated the hepatic mRNA expression of the cholesterol biosynthesis enzyme, 3-hydroxy-3-methylglutaryl-CoA reductase, whereas high levels of dietary PO significantly upregulated the expression of the critical regulatory enzyme of bile acid biosynthesis, cholesterol 7-alpha-hydroxylase. In conclusion, poultry oil is a good substitution for fish oil in the diets of tiger puffer. Poultry oil could replace 100% added fish oil in the diet of tiger puffer, without adverse effects on growth and body composition.

The fish oil finishing (FOF) strategy, that is, re-feeding fish with fish oil (FO)-based diet after a certain period of feeding with alternative lipid source-based diets. On tiger puffer, the present study investigated the response of intestinal microbiota to FOF. Fish were fed four diets based on FO, soybean oil, palm oil and beef tallow as lipid sources, respectively, firstly for 50 days (growing-out period), and then fed the FO-based diet for 30 more days (FOF period). The results showed that dietary terrestrially sourced oils impaired the intestinal function in the growing-out period. However, the activities of amylase, trypsin and anti-oxidative enzymes (SOD, CAT, T-AOC), as well as gene expression of inflammatory cytokines (IL-1β, TNF-α, TGF-β) and tight junction protein (Claudin4, Claudin7, Claudin18, JAM, ZO-1) in the intestine were significantly recovered by FOF. The 16S rDNA sequencing analysis showed that FOF improved the similarity of bacterial community among the groups. The MetaStat analysis confirmed that FOF regulated the abundance of butyric acid-producing bacteria (Lachnospiraceae, Eubacterium, Butyricicoccus, Clostridium and Roseburia) and bacteria related to digestion and absorption (Sphingomonas, Romboutsia and Brevibacillus). In conclusion, FOF can recover the intestine function. The intestinal microbiota probably participated in and played a key role in the recovery process.

An 8-week feeding trial was conducted, where turbot were fed four experimental diets, containing different LPC levels (0%, 0.1%, 0.25%, and 0.5%, named LPC0, LPC0.1, LPC0.25, and LPC0.5, respectively). The intestinal morphology results showed that there were no widened lamina propria and mixed inflammatory cells in the LPC-supplemented groups. Dietary LPC remarkably decreased the expression of TLRs (TLR3, TLR8, TLR9, and TLR22), MyD88, and signaling molecules (NF-κB, JNK, and AP-1). Similarly, diets with LPC supplementation markedly depressed the gene expression of NF-κB and JNK signaling pathway downstream genes (TNF-α, IL-1β, Bax, Caspase9, and Caspase-3). Furthermore, dietary LPC modified the intestinal microbial profiles, increasing the relative abundance of short-chain fatty acids-producers, lactic acid bacteria, and digestive enzyme-producing bacteria. Predictive functions of intestinal microbiota showed that turbot fed LPC diets had a relatively higher abundance of functions, such as lipid metabolism and immune system, but a lower abundance of functions, such as metabolic diseases and immune system diseases. The activities of intestinal acid phosphatase and alkaline phosphatase were also increased by dietary LPC. In conclusion, LPC supplementation could regulate the intestinal mucosal barrier via the TLR signaling pathway and alter the intestinal microbiota profile of turbot fed high-lipid diets.

This study aimed to evaluate effects of fish protein hydrolysate (FPH) supplementation in plant protein based diets for tiger puffer (Takifugu rubripes) on growth performance, intestinal peptide and amino acid transporters, and the expression of protein synthesis-related genes and texture parameters in muscle. Tiger puffer were fed negative and positive control diets with 280 and 400 g/kg fish meal (LFM and HFM) or test diets containing 52 and 104 g/kg FPH supplement as 60 and 120 g/kg fish meal (FPH6 and FPH12) substitute for 56 days. Each diet was randomly fed to triplicate groups of 30 fish per tank. Growth parameters (final body weight, weight gain and specific growth rate) in the LFM group were significantly lower than that of the HFM group (p < 0.05), while no differences in those growth results were observed among the FPH6, FPH12 and HFM groups (p > 0.05). Compared with the LFM group, the expressions of intestinal PepT1, EAAT3, PAT1 and y+LAT2 were up-regulated in the FPH12 and HFM groups, while intestinal CAT1 and B°AT1 mRNA levels showed opposite trends. To protein synthesis-related gene expression, compared with the LFM group, mRNA levels of TOR and S6k1 was not significantly affected by dietary treatments, but mRNA level of 4E-BP1 increased in the FPH12 group. Lower chewiness and higher adhesiveness were observed when FPH was supplemented to the diets. In conclusion, FPH supplementation in plant protein based diets demonstrated a sparing effect on fish meal, without the negative effect on the growth of tiger puffer.

Omics approaches provide more metabolic information to explain the relationship between dietary nutrition and fish growth. This study aimed to explore the metabolome and proteome response of turbot (Scophthalmus maximus) fed diets containing lysine and leucine in free and dipeptide forms by the approaches of integrated liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based metabolomics and isobaric tags for relative and absolute quantification (iTRAQ)-based proteomics. Plant protein-based diets were formulated to contain the equivalent of lysine and leucine in free amino acid [crystalline amino acid (CAA)] and synthetic Lys-Leu (Lys-Leu) forms. The metabolome and proteome profiles of the liver were screened in fish fed either the CAA diet or the Lys-Leu diet after an 8-week feeding trial. Fish fed the Lys-Leu diet showed a significantly higher final body weight and a specific growth rate compared with fish fed the CAA diet. Protein- and amino acid-related metabolic processes in the liver were identified between the Lys-Leu and CAA groups based on differential metabolites and proteins. The proteolytic enzymes and amino acid transporters from differential proteins of the liver showed that the process of protein digestion and absorption may be affected by the different forms of lysine and leucine in the feed. A mechanistic target of rapamycin complex 1 and ubiquitin proteasome pathways were identified by differential proteins, which were involved in the processes of protein synthesis and degradation in the liver. Lysine degradation, tryptophan metabolism, alanine, aspartate, and glutamate metabolism, arginine biosynthesis, arginine and proline metabolism, and glycine, serine, and threonine metabolism were identified based on differential metabolites and proteins, which showed that the metabolism of various amino acids, including lysine, had been affected by both the CAA and Lys-Leu groups. In conclusion, the data of integrated metabonomics and proteomics suggested that different forms of lysine and leucine in the feed may affect liver metabolic processes including protein digestion and absorption, protein synthesis and degradation, and amino acid metabolism. In addition, a good correlation between differential metabolites and proteins was observed in amino acid metabolism by using the approaches of integrated LC-MS/MS-based metabolomics and iTRAQ-based proteomics.

Mid1ip1 plays important roles in lipogenesis and microtubule stabilization, but little relevant information has been reported in fish. In the present study, mid1ip1 cDNA of tiger puffer was cloned and characterized, and its expression in response to dietary bile acid and lipid levels was investigated following a feeding trial. Experimental diets with suitable (8.5 %) or high lipid level (12.5 %), with or without bile acid supplementation (0.02 % and 0.10 % in the suitable-lipid diet; 0.02 % in the high-lipid diet) were used in the feeding trial. The tiger puffer Mid1ip1, which is putative Mid1ip1 subtype B, shared moderate identity to its known orthologs of other teleost and much lower identity to human Mid1ip1. Mid1ip1 had high transcription in the muscle, skin, eye, and brain, but low expression levels in the liver, intestine, and spleen. The high dietary bile acid level (0.1 %) significantly (P 0.05) affect the gene expression. Significantly positive correlation (R2 = 0.812, P = 0.000) was observed between hepatic mRNA expression of mid1ip1 and tubulin-α, but not between the gene expression of mid1ip1 and acetyl-CoA carboxylase β (R2 = -0.434, P = 0.106), in response to dietary treatments, indicating the potential roles of this Mid1ip1 subtype in microtubule stabilization rather than in lipogenesis. To our knowledge, this is the first study investigating the regulation of fish mid1ip1 expression by dietary nutrients.

Our previous studies have shown that ARA regulated the gonadal steroidogenesis and the synthesis of gonadotrophin-releasing hormone (GnRH) in the brain in a gender-dependent manner in Chinese tongue sole, a marine teleost with typical sex dimorphism. As a following up-study, the current study aimed to clone and characterize a gene responding to dietary ARA differently between males and females, cholesterol 25-hydroxylase (ch25h), which has important roles in cholesterol and lipid metabolism of mammals, but is rarely investigated in fish. The full-length cDNA of Chinese tongue sole ch25h was cloned and characterized, and its transcription in the gonads, brain and liver of both males and females in response to dietary ARA levels (0.34, 2.53, and 9.63% of TFA) was investigated. The Chinese tongue sole Ch25h, which putatively is Ch25h subtype B, shared moderate identity to its known orthologs of other teleost and lower identity to human Ch25h. It has high transcription levels in the gonads, followed by skin and muscle, but low levels in the intestine, spleen, and kidney. High ARA levels significantly increased the ch25h transcription in the gonads and brain of male fish, but did not affect the transcription in the females. However, the effect of dietary ARA on ch25h transcription in the liver showed an opposite gender-difference pattern to those in the gonads and brain. To our knowledge, this is the first study in marine teleost investigating the nutritional regulation of ch25h expression.

Abstract To investigate the physiological roles of dietary arachidonic acid (ARA) in fish, a feeding trial with Japanese seabass was conducted, followed by a hepatic transcriptome assay. Six experimental diets differing basically in ARA level (0.05%, 0.22%, 0.37%, 0.60%, 1.38% and 2.32% of dry matter) were used in the feeding trial. Liver samples from fish fed diets with 0.05% and 0.37% ARA were subjected to transcriptomic assay, generating a total of 139 differently expressed unigenes, which were primarily enriched in lipid metabolism and cell cycle-related signaling pathways. Then, qRT-PCR validation on lipid metabolism and cell cycle-related genes as well as corresponding enzyme-linked immunosorbent assay of selected proteins were conducted with liver samples from all six groups. Moderated ARA levels reduced lipogenesis and stimulated β-oxidation concurrently, but high ARA levels seemed to affect lipid metabolism in complicated ways. Both gene expression and protein concentration of cell cycle-related proteins were decreased by moderate levels of dietary ARA. The lipid content and fatty acid composition in fish confirmed the transcription and protein concentration results related to lipid metabolism. In conclusion, moderate levels of dietary ARA (0.37% and 0.60%) reduced lipid accumulation and tended to inhibit cell cycle progression in the liver of Japanese seabass.

Long non-coding RNAs (lncRNA) have emerged as important regulators of lipid metabolism and have been shown to play multifaceted roles in controlling transcriptional gene regulation, but very little relevant information has been available in fish, especially in non-model fish species. With a feeding trial on a typical marine teleost tongue sole C. semilaevis followed by transcriptomic analysis, the present study investigated the possible involvement of lncRNA in hepatic mRNA expression in response to different levels of dietary DHA and EPA, which are two most important fatty acids for marine fish. An 80-day feeding trial was conducted in a flow-through seawater system, and in this trial three experimental diets differing basically in DHA/EPA ratio, i.e., 0.61 (D/E-0.61), 1.46 (D/E-1.46), and 2.75 (D/E-2.75), were randomly assigned to 9 tanks of experimental fish. A total of 124.04 G high quality genome-wide clean data about coding and non-coding transcripts was obtained in the analysis of hepatic transcriptome. Compared to diet D/E-0.61, D/E-1.46 up-regulated expression of 178 lncRNAs and 2629 mRNAs, and down-regulated that of 47 lncRNAs and 3059 mRNAs, while D/E-2.75 resulted in much less change in gene expression. The co-expression and co-localization analysis of differentially expressed (DE) lncRNA and mRNA among dietary groups were then conducted. The co-expressed DE lncRNA and mRNA were primarily enriched in GO terms such as Metabolic process, Intracellular organelle, Catalytic activity, and Oxidoreductase activity, as well as in KEGG pathways such as Ribosome and Oxidative phosphorylation. Overlap of co-expression and co-localization analysis, i.e., lncRNA–mRNA matches “XR_523541.1–solute carrier family 16, member 5 (slc16a5)” and “LNC_000285–bromodomain adjacent to zinc finger domain 2A (baz2a),” were observed in all inter-group comparisons, indicating that they might crucially mediate the effects of dietary DHA and EPA on hepatic gene expression in tongue sole. In conclusion, this was the first time in marine teleost to investigate the possible lncRNA–mRNA interactions in response to dietary fatty acids. The results provided novel knowledge of lncRNAs in non-model marine teleost, and will serve as important resources for future studies that further investigate the roles of lncRNAs in lipid metabolism of marine teleost.

The present study was conducted to investigate the effects of dietary DHA and EPA on gonadal steroidogenesis in mature females and males, with a feeding trial on tongue sole, a typical marine teleost with sexual dimorphism. Three experimental diets differing basically in DHA:EPA ratio, that is, 0·68 (diet D:E-0·68), 1·09 (D:E-1·09) and 2·05 (D:E-2·05), were randomly assigned to nine tanks of 3-year-old tongue sole (ten females and fifteen males in each tank). The feeding trail lasted for 90 d before and during the spawning season. Fish were reared in a flowing seawater system and fed to apparent satiation twice daily. Compared with diet D:E-0·68, diet D:E-1·09 significantly enhanced the oestradiol production in females, whereas diet D:E-2·05 significantly enhanced the testosterone production in males. In ovaries, diet D:E-1·09 induced highest mRNA expression of follicle-stimulating hormone receptor (FSHR), steroidogenic acute regulatory protein, 17a-hydroxylase (P450c17) and 3β-hydroxysteroid dehydrogenase (3β-HSD). In testes, diet 2·05 resulted in highest mRNA expression of FSHR, cholesterol side-chain cleavage enzyme, P450c17 and 3β-HSD. Fatty acid profiles in fish tissues reflected closely those of diets. Female fish had more gonadal EPA content but less DHA content than male fish, whereas there was a reverse observation in liver. In conclusion, the dietary DHA: EPA ratio, possibly combined with the dietary EPA:arachidonic acid ratio, differentially regulated sex steroid hormone synthesis in mature female and male tongue soles. Females seemed to require more EPA but less DHA for the gonadal steroidogenesis than males. The results are beneficial to sex-specific nutritive strategies in domestic teleost. [ABSTRACT FROM AUTHOR]

Japanese seabass, Lateolabrax japonicus (mean initial weight 204.5 g) were fed one of six casein-dextrin-based diets containing graded levels of magnesium (Mg) (184, 278, 487, 929, 1299, and 1737 mg/kg) for 10 weeks with the water-borne Mg concentration of 985 mg/L. Magnesium sulphate was used as the Mg source in the diets. The experiment was carried out in floating sea cages. Growth, survival rate, superoxide dismutase (SOD) activities, glutathione peroxidase (GPx), malondiadehyde (MDA) contents and tissue mineral contents were measured to investigate the effect of dietary magnesium in seabass. After 10 weeks, dietary magnesium supplementation did not improve the growth performance or feed efficiency of adult seabass. On the contrary, negative effects on growth performance, decreased glutathione peroxidase (GPx) and increased malondiadehyde (MDA) contents were observed in seabass fed Mg diets with 929, 1299 mg/kg and 1737 mg/kg, and feed efficiency (FE) exhibited a decreasing tendency with increasing Mg supplemental levels, which indicates the Mg requirement of seabass was met in fish fed the basal diet. Survival, hepatosomatic index, viscerosomatic index, condition factor, and Mg and Ca concentration in wholebody, vertebrae, and scales were not affected by dietary Mg supplementation (P<0.05). [ABSTRACT FROM AUTHOR]

A 10-week growth trial was conducted to investigate the effect of dietary cornstarch levels on the growth performance, body composition, liver/muscle glycogen, and selected serum biomarkers, of Japanese seabass in grow-out phase. Six isonitrogenous and isolipidic diets containing graded levels (0%, 6%, 12%, 18%, 24%, 30%) of cornstarch were fed to Japanese seabass (initial weight 343g). Weight gain (WG) significantly increased up to 18% with increasing dietary cornstarch, and then reached a plateau. There was no significant difference in WG between fish fed 18%, 24%, or 30% cornstarch (P>0.05). Based on WG, the optimal dietary cornstarch level of Japanese seabass estimated by second-order polynomial model was 27.0%. Body protein and lipid content as well as total cholesterol and triglycerides in serum showed similar trends, i.e. increasing at first and then reaching a plateau despite increasing levels of dietary cornstarch. Ash content decreased at first and then reached a plateau with increasing dietary cornstarch. Hepatosomatic index and liver glycogen significantly increased with increasing dietary cornstarch (P<0.05) while muscle glycogen, the condition factor was not influenced by dietary treatments. Serum glucose significantly increased with increasing dietary cornstarch and then decreased (P<0.05). Results of this study suggest the provision of adequate dietary cornstarch (>18%) could improve the growth performance of Japanese seabass and the optimal dietary cornstarch level is 27.0% during grow out phase. [ABSTRACT FROM AUTHOR]

The optimal lipid requirements in Japanese seabass of two different sizes (initial body weight, 34.26±0.37 g, and 343.3±10.0 g) were tested using the same experimental diets in two feeding trials (trial I and trial II). Five experimental diets were formulated to obtain graded dietary lipid levels: 0.6%, 3.9%, 7.3%, 11.7%, and 15.8%. Each diet was randomly assigned to triplicate groups of fish. Both feed trials lasted 10 weeks. The results in both feeding trials showed that specific growth rate significantly increased by increasing dietary lipid levels from 0.6% to 7.3%, and declined thereafter. Based on the specific growth rate, the optimum dietary lipid requirement of the small and large Japanese seabass was 7.4% and 9.9% respectively. The increasing dietary lipid levels significantly increased the fish body protein concentration, but only in feeding trial II. In both feeding trials, the lipid contents in whole fish body and liver significantly increased with increasing dietary lipid levels, but the small fish showed much lower lipid content than the large fish. The serum triglyceride concentrations in the small fish were higher than those in the large fish. High levels of dietary lipid (3.9% and 7.3%) reduced the serum cholesterol concentrations in the small fish, which was much lower than those in the large fish. These results suggested that the lipid requirements, as well as the body composition and lipid deposition differed according to the size of growing Japanese seabass. The results are important for feed formulation for aquaculture of different sized Japanese seabass throughout their production cycle. [ABSTRACT FROM AUTHOR]

A 60-day feeding experiment was conducted to investigate the effects of dietary lipid sources on reproduction of Cynoglossus semilaevis. Experimental diets were formulated with similar proximate compositions but different lipid sources (6.5%): fish oil (FO), soybean oil (SO) and olive oil (OO). The results showed that the relative fecundity in group FO and OO was significantly higher than that in group SO. Group OO showed a significantly higher buoyant egg rate than group FO and SO. The hatching rate and larval survival rate at 7 days post hatching were the highest in group FO, followed by group OO, and group SO recorded the lowest values. Group FO showed significantly higher egg diameter and larval survival activity index (SAI) and significantly lower larval deformity rate compared to group SO and OO. Fatty acid compositions of eggs reflected closely those of the diets. These results showed that the olive oil supplement in diets for tongue sole positively influenced the broodstock fecundity and buoyant egg rate though fish oil resulted in the highest hatching rate and best larval quality among the tested oils. The dietary soybean oil supplement reduced the spawning performance, and egg and larval quality. [ABSTRACT FROM AUTHOR]

The article determines the effect of different protein sources on the performance of larval tongue sole Cynoglossus semilaevis. The effect of supplementation of meals for fish, shrimp, mussel or fish protein hydrolysate was measured in a microdiet on growth and survival of tongue sole larvae. Authors of the study indicated positive effects on fish performance due to the inclusion of protein hydrolysate as partial or total replacement for native proteins in diets. The study indicated that fish protein hydrolysate showed potential as an ingredient in tongue sole larvae diet.

The article examines the effects of different levels of fish protein hydrolysate in the diet on the non-specific immunity of Japanese sea bass (Lateolabrax japonicus), one of the main fish cultured in China. As stated in the article, infectious diseases are becoming more common in fish culture. To reduce the incidence of many important diseases in fish aquaculture, vaccinations for fish pathogens and antibiotics used to control these diseases were applied. These antibiotics can result in the development of drug-resistant bacteria, environmental protection and residues in fish.