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The tissue distribution pattern of lipid is highly diverse among different fish species. Tiger puffer has a special lipid storage pattern, storing lipid predominantly in liver. In order to better understand the lipid physiology in fish storing lipid in liver, the present study preliminarily investigated the tissue distribution of transcription for 29 lipid metabolism-related genes in tiger puffer, which are involved in lipogenesis, fatty acid oxidation, biosynthesis and hydrolysis of glycerides, lipid transport, and relevant transcription regulation. Samples of eight tissues, brain, eye, heart, spleen, liver, intestine, skin, and muscle, from fifteen juvenile tiger puffer were used in the qRT-PCR analysis. The intestine and brain had high transcription of lipogenic genes, whereas the liver and muscle had low expression levels. The intestine also had the highest transcription level of most apolipoproteins and lipid metabolism-related transcription factors. The transcription of fatty acid β-oxidation-related genes was low in the muscle. The peroxisomal fatty acid oxidation may dominate over mitochondrial β-oxidation in the liver and intestine of tiger puffer, and the MAG pathway probably predominates over the G3P pathway in re-acylation of absorbed lipids in the intestine. The intracellular glyceridases were highly transcribed in the brain, eye, and heart. In conclusion, in tiger puffer, the intestine could be a center of lipid metabolism whereas the liver is more likely a pure storage organ for lipid. The lipid metabolism in the muscle could also be inactive, possibly due to the very low level of intramuscular lipid.

Taurine (TAU) plays important roles in the metabolism of bile acids, cholesterol and lipids. However, little relevant information has been available in fish where TAU has been identified as a conditionally essential nutrient. The present study aimed to investigate the effects of dietary TAU on the metabolism of bile acids, cholesterol and lipids in tiger puffer, which is both an important aquaculture species and a good research model, having a unique lipid storage pattern. An 8-week feeding trial was conducted in a flow-through seawater system. Three experimental diets differed only in TAU level, that is, 1·7, 8·2 and 14·0 mg/kg. TAU supplementation increased the total bile acid content in liver but decreased the content in serum. TAU supplementation also increased the contents of total cholesterol and HDL-cholesterol in both liver and serum. The hepatic bile acid profile mainly includes taurocholic acid (94·48 %), taurochenodeoxycholic acid (4·17 %) and taurodeoxycholic acid (1·35 %), and the contents of all these conjugated bile acids were increased by dietary TAU. The hepatic lipidomics analysis showed that TAU tended to decrease the abundance of individual phospholipids and increase those of some individual TAG and ceramides. The hepatic mRNA expression study showed that TAU stimulated the biosynthesis of both bile acids and cholesterol, possibly via regulation of farnesoid X receptor and HDL metabolism. TAU also stimulated the hepatic expression of lipogenic genes. In conclusion, dietary TAU stimulated the hepatic biosynthesis of both bile acids and cholesterol and tended to regulate lipid metabolism in multiple ways.

The study aimed to investigate the effects of crystalline Lys and Leu, Lys‐Leu dipeptide and Lys‐Leu‐Lys/Leu‐Lys‐Leu tripeptide, on growth, postprandial Lys and Leu concentrations, gene expression of peptide and amino acid (AA) transporters and related gene expression of protein synthesis pathway in turbot. Three diets (CAA, Di and Tri) contained Lys and Leu as free (Lys and Leu), dipeptide (Lys‐Leu) and tripeptide (Lys‐Leu‐Lys/Leu‐Lys‐Leu) forms, respectively. Improved growth was observed in the Di group compared with the CAA group. For peptide and AAs transporters, PepT1, B⁰AT1 and y⁺LAT2 mRNA levels were affected in proximal intestine by dietary treatments. Free Lys and Leu concentrations in the CAA group were significantly higher than that of the Di and Tri groups at 6 hr postfeeding in serum and at 2, 6 and 24 hr postfeeding in muscle. For protein synthesis pathway in muscle, Akt2, TOR and S6k1 gene expression were the highest in the Di group and the lowest in the CAA group, whereas MuRF1 relative expression was the highest in the Tri group. In conclusion, dietary Lys‐Leu dipeptide was utilized more efficiently than free Lys and Leu or Lys‐Leu‐Lys/Leu‐Lys‐Leu tripeptide for turbot by regulating AAs transport, postprandial AAs concentration and the synthesis of muscle proteins.

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.

The effects of fish protein hydrolysate (FPH) on growth, peptide and amino acid (AA) transporters, postprandial free AA and related gene expression of IGF‐1/AKT pathway were evaluated in turbot (Scophthalmus maximus). Three diets were formulated to contain the same low level of fishmeal; meanwhile 0, 45 and 180 g/kg FPH were, respectively, supplemented to the FF (FPH‐free), FL (FPH‐Low) and FH (FPH‐High) diets. Fish fed the FH diet improved the growth compared with the other groups. For peptide and AA transporters, PepT1, B⁰AT1, CAT1 and PAT1 mRNA levels in proximal or distal intestine decreased in fish fed the FH diet. The concentration of free total essential AAs in serum was higher in the FH treatment than that in the FF treatment at 2 and 6 hr after feeding. For IGF‐1/AKT pathway in muscle, IGF‐1, 4E‐BP1 and FoxO1 mRNA levels were the highest in the FH group, whereas IGF‐1R mRNA levels were the highest expression level in the FF group. In conclusion, down‐regulated AAs transport, alleviated the delayed postprandial peak of serum‐free AAs and increased muscle protein synthesis were observed to improve the growth when turbot was fed high FPH level diets containing a high plant protein.

A 74‐day feeding trial was conducted to investigate the efficacy of n‐6 polyunsaturated fatty acid (n‐6 PUFA) in diets for tiger puffer. Six experimental diets with graded levels of n‐6 PUFA (from 6.01 to 37.98 g/kg) replacing saturated fatty acids (SFAs) were used in this study. Increasing levels of n‐6 PUFA resulted in decreased weight gain (from 472.6% to 349.4%), feed efficiency and crude protein content in fish, but increased lipid accumulation in whole fish and liver. Liver samples from fish fed the lowest and highest level of n‐6 PUFA were subjected to transcriptomic assay. Analysis of the differentially expressed genes showed that high dietary levels of n‐6 PUFA tended to induce glycolysis and triacylglycerol biosynthesis, but reduce synthesis of amino acid and protein, and cause impairment to liver health. The mitochondrial DNA copy number, activity of mitochondrial respiratory chain complex I and glycogen content in the liver, which indicate energy supply status, significantly decreased with increasing levels of dietary n‐6 PUFA. In conclusion, high n‐6 PUFA/SFA ratios in diet led to reduced energy supply (by approximately 50%) and increased hepatic lipid accumulation (by 55%), which probably consequently negatively affect protein synthesis, liver health and growth of tiger puffer.

A 74-day feeding trial was conducted to investigate the effects of different levels of dietary arachidonic acid (ARA) on mucosal barrier and microbiota in the intestine of tiger puffer Takifugu rubripes. Three isonitrogenous and isolipidic experimental diets were formulated to contain different ARA levels, i.e., 0.33 (Control), 2.45 (L-ARA), and 23.41 (H-ARA) g kg−1 dry matter. Each diet was fed to triplicate tanks. The results showed that the integrity of intestinal epithelial cells was impaired by increasing ARA levels. The leucocyte infiltration in the lamina propria was also enhanced by dietary ARA supplementation. Compared to the control group, group H-ARA had significantly down-regulated gene expression of intestinal tight junction proteins (claudin-4, claudin-7 and zonula occludens-1), but significantly up-regulated expression of myosin light chain kinase (MLCK). Gene expression of claudin-7 was significantly down-regulated also in group L-ARA. The intestinal lysozyme activity significantly decreased with increasing dietary ARA levels. Compared to the Control, diet H-ARA significantly up-regulated the gene expression of the pro-inflammatory cytokines tumor necrosis factor alpha (TNF-α) and interleukin 8 (IL-8), and down-regulated that of anti-inflammatory cytokines transforming growth factor-β1 (TGF-β1) in the hind intestine. Intestinal gene expression of Toll-like receptor 3 (TLR-3) and nuclear factor kappa B p100 (NF-κB p100) was significantly up-regulated by H-ARA. Sequencing of bacterial 16 s rRNA V4 region showed that Proteobacteria, Tenericutes and Firmicutes were dominant in the intestine of tiger puffer. Fish fed diet H-ARA showed significantly decreased alpha diversity of microbiota and increased relative abundance of Arcobacter, a potential pathogenic genus. These results suggested that dietary ARA tended to induce the dysfunction of intestinal mucosal barrier and modulate the intestinal bacterial community, and MLCK and TLR3/NF-κB signaling were possibly involved in these processes. The ARA content in diets for tiger puffer needs to be carefully managed considering the intestinal sensitivity to dietary ARA of this fish.

A 10‐week feeding experiment in indoor flow‐through seawater system was conducted to investigate the effects of dietary krill hydrolysate on the expression of growth‐related genes in juvenile turbot (Scophthalmus maximus L.; initial body weight 9.45 ± 0.01 g). Three isonitrogenous and isolipidic experimental diets containing high plant protein were formulated to contain 0 (control), 50 g/kg (LKH) and 100 g/kg (HKH) krill protein hydrolysate (KH) to replace fishmeal, respectively. Triplicate groups of 30 fish were fed for 10 weeks to apparent satiation twice daily. At the end of the feeding trial, the mRNA expressions of insulin‐like growth factor (IGF‐1) gene in liver, peptide transporters (PepT1) gene in pyloric caeca and proximal intestine and neuropeptide Y (NPY) gene in brain in all groups were determined. IGF‐1, PepT1 and NPY expression levels in HKH group were significantly increased compared with those of LKH and control (p

The present study was conducted to investigate the effects of dietary DHA/EPA ratio on lipid accumulation in farmed fish, with an 80-day feeding trial on tongue sole Cynoglossus semilaevis, a typical marine flatfish. Six experimental diets differing basically in DHA/EPA ratio, i.e., 0.61, 1.02, 1.46, 1.91, 2.32, and 2.75, were randomly assigned to 18 tanks of juvenile tongue sole. Fish were reared in a flow-through seawater system and fed to apparent satiation twice daily. Compared to very low (0.61) or high (2.32 and 2.75) dietary DHA/EPA levels, moderate dietary DHA/EPA ratios of 1.02 and 1.46 induced higher lipid accumulation in fish flesh and whole fish. Although also inducing increased liver lipid accumulation, the moderate dietary DHA/EPA ratios did not compromise the fish health in terms of growth performances and hematological parameters. The fatty acid profile of fish tissues reflected closely those of the diets, but DHA had more efficient deposition in fish flesh than EPA. Excess EPA or DHA in diets down-regulated the mRNA expression of lipogenic genes in fish tissues, and DHA seemed to be more efficient than EPA in up-regulating gene expression of β-oxidation-related proteins. Both esterification and hydrolyzation of triglycerides in fish tissues seemed to be more active in groups with intermediate DHA/EPA ratios (1.02 and 1.46). The present study provided a new way to modulate the nutritive quality of farmed fish, as well as to make better use of precious LC-PUFA resources.

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.

A 70-day feeding trial with Pacific white shrimp ( Litopenaeus vannamei ) broodstocks was conducted before eyestalk ablation to investigate the effects of arachidonic acid (ARA) in diets for early maturation stages on the final reproductive performances. Three isonitrogenous and isolipidic experimental diets were formulated to contain different ARA levels: the control diet without ARA supplementation (C, 0.87% ARA of total fatty acids (TFA)) and two diets with low (4.65% of TFA, ARA-L) or high ARA (12.39% of TFA, ARA-H) supplementation level. The diets were randomly assigned to 9 tanks of eight-month-old Pacific white shrimp broodstock (30 females and 30 males in each tank). Shrimp were reared in a flowing seawater system and fed to apparent satiation four times daily. At the end of the feeding trial, unilateral eyestalk of the females was ablated to stimulate the gonad maturation. Following the feeding trial (Period I) was a 28-day reproductive evaluation period (Period II), during which all shrimps were fed the same fresh invertebrate ingredients (a mixture of squid and polychaetes). Tissues samples of females were collected at the end of the feeding trial (Period I) and before spawning (ready to spawn) at the reproductive evaluation period (Period II) respectively to measure the gonadosomatic index (GI), hepatopancreas index (HI), estradiol level, and fatty acid composition. The spawning performance and quality of egg and larvae were assayed at Period II. The results showed that compared to the control group, ARA-L increased the GI at Period II while the ARA supplemented diets increased the estradiol synthesis at Period I. The HI was not influenced by dietary ARA level. Compared to the control group, ARA-L but not ARA-H significantly increased the spawning rate, multi-spawning rate, average spawning frequency and fecundity of female shrimp, diameter of fertilized egg, and crude metamorphosis rate of nauplii at 33 h post spawning. The hatching rate significantly ranked as follows: C

In this study, putative cDNA of three fatty acid transport protein (FATP) isoforms, that is FATP1, FATP4 and FATP6, was cloned and characterized from the liver of Japanese seabass (Lateolabrax japonicus), and their expression in response to diets with different arachidonic acid (ARA) levels (0.05%, 0.22%, 0.37%, 0.60%, 1.38% and 2.32% of dry matter) was investigated through a feeding trial. Two subtypes of FATP1, that is FATP1a and FATP1b, were cloned for the first time. The Japanese seabass FATPs showed high identity to their orthologs in other fish species and mammals, but Japanese seabass FATP6 showed low identity to Japanese seabass FATP1 and FATP4. FATP1a gene was highly expressed in brain, liver and eye, whereas FATP1b had the highest gene expression in gill, followed by kidney, skin, eye, muscle and heart. FATP4 gene was primarily expressed in intestine, brain and eye. However, FATP6 had very low gene expression levels in almost all tissues. High levels of dietary ARA (0.60%~2.32%) enhanced the gene expressions of FATP1a and FATP4 in the intestine and the gene expression of FATP1a in the muscle, whereas the dietary ARA supplementation reduced the FATP1b mRNA expression in the liver. The gene expression of FATP1a, FATP4 and FATP6 in the liver, as well as the FATP4 gene expression in the muscle, was not significantly affected by dietary ARA levels. To our knowledge, this is the first study investigating the regulation of FATP gene expressions by dietary ARA.

A three-month feeding trial was conducted to investigate the effects of dietary krill meal on the reproductive performance of tongue sole broodstock. Three diets were formulated to contain different levels of krill meal, 0 (Diet K-0), 10 (K-100) and 200 (K-200) g kg–1 dry matter, replacing the corresponding contents of protein and lipid from fishmeal and fish oil. Each diet was assigned to triplicate tanks. Compared with K-0, both K-100 and K-200 increased the egg properties such as buoyant eggs rate, egg diameter, oil droplet diameter and SOD activity of the fertilized egg. However, the maturation rate, serum estradiol content, the relative fecundity and hatching rate were improved only by K-100. The krill meal supplementation increased the concentrations of astaxanthin and n-3 fatty acids in eggs, but decreased the n-6 fatty acid concentrations. Both K-100 and K-200 increased the survival activity index, but the larval deformity rate was decreased only by K-100. At 15 DPH, the larval length and the digestive enzyme activities were significantly higher in group K-200 compared with groups K-0 and K-100. In conclusion, dietary supplementation of krill meal, at the level of 100 or 200 g kg–1 dry matter in exchange of fishmeal and fish oil had the considerable positive effects on C. semilaevis reproduction.

In the present study, putative cDNA of five fabp isoforms, i.e., fabp1, fabp2, fabp3, fabp4, and fabp7, was cloned and characterized from the liver of Japanese seabass (Lateolabrax japonicus), and their expression in response to diets with different arachidonic acid (ARA) levels (0.05%, 0.22%, 0.37%, 0.60%, 1.38% and 2.32% of dry matter) was investigated following a feeding trial. The Japanese seabass fabps showed high identity to their orthologs in other fish species and mammals. However, a specific fabp of Japanese seabass showed much lower identity to other Japanese seabass fabps. fabp1 has high expressions in liver and intestine, whereas fabp2 is mainly expressed in the gastrointestinal tract. The highest expression level of fabp3, fabp4, and fabp7 was observed in muscle, eye, and liver respectively. Different tissue expression patterns of fabp2, fabp4, and fabp7 between Japanese seabass and other teleost may indicate specific evolutionary Fabp functions in Japanese seabass. Moderate levels of dietary ARA (0.37-0.60%) enhanced the gene expressions of fabp1 in liver and intestine, fabp2 in intestine, and fabp3 in intestine, whereas excess dietary ARA levels (1.38-2.323%) were ineffective. The highest level of dietary ARA (2.32%) increased only the expression of fabp3 in muscle compared to the control diet. Gene expressions of fabp3 and fabp7 in liver, and fabp4 in liver, intestine, and muscle were not significantly influenced by dietary ARA. To our knowledge, this is the first study investigating the regulation of fabp expressions by dietary ARA.

A 3-month feeding trial with tongue sole Cynoglossus semilaevis broodstock was conducted before and during the spawning season to investigate the effects of dietary arachidonic acid (ARA) on the production of sex steroid hormones and gonadal gene expression of key proteins in steroidogenesis. Three isonitrogenous and isolipidic experimental diets were formulated to contain different ARA levels: the control diet without ARA supplementation (C, 0.58% ARA of total fatty acids (TFA)) and two diets with low (5.14% of TFA, ARA-L) or high ARA (15.44% of TFA, ARA-H) supplementation. The diets were randomly assigned to 9 tanks of 3-year-old tongue sole (10 females and 15 males in each tank). Fish were reared in a flowing seawater system and fed to apparent satiation twice daily. At the end of the feeding trial, tissue samples from mature females (MF, with spontaneous ovulation), immature females (IMF, early vitellogenesis), and mature males (MM, expressing milt) were collected to assay the production of sex steroid hormones, gonadal gene expression of sex steroid-synthesizing proteins, as well as the fatty acid profiles of gonad, liver and muscle lipids. Results showed that ARA supplementation significantly reduced the estradiol production in females, but stimulated the testosterone production in males. ARA supplementation significantly reduced the mRNA expression of aromatase in ovaries but significantly increased the gene expression of 3β-hydroxysteroid dehydrogenase (3β-HSD) in testes. In mature ovaries, diet ARA-L significantly reduced the gene expression of follicle stimulating hormone receptor (FSHR), 3β-HSD, and 17β-HSD; however, in immature ovaries, it significantly increased the gene expression of FSHR, steroidogenic acute regulatory protein (StAR), cholesterol side-chain cleavage enzyme (P450ssc), 3β-HSD, and 17β-HSD. In all gonads, 17α-hydroxylase (P450c17) responded to dietary ARA differently from other sex steroid-synthesizing proteins. ARA was preferentially accumulated in tongue sole gonad lipids. ARA concentrations were highest in gonad, liver and muscle lipids of MM fish and lowest in MF fish. Compared to female tongue sole, males had higher DHA concentrations in gonad lipids, but lower concentrations in liver lipids. In conclusion, results suggest dietary ARA regulates sex steroid hormone synthesis in tongue sole broodstock, and accumulates in gonad lipids, depending on both fish gender and maturation stage. Dietary ARA supplementation appears more important for male fish than for female fish, and more important for immature females than for mature females. Statement of relevance This study is beneficial to the broodstock diet formulation.

This study was conducted to evaluate the effects of different dipeptides (lysine-leucine, lysine-glycine, and leucine-glycine) and free amino acids (lysine and leucine) on the growth, gene expression of intestinal peptide and amino acid transporters, and serum free amino acid concentrations in turbot. Fish (11.98 ± 0.03 g) were fed four experimental diets supplementing with crystalline amino acids (CAA), lysine-leucine (Lys-Leu), lysine-glycine (Lys-Gly), and leucine-glycine (Gly-Leu). Fish protein hydrolysate (FPH) containing a mixture of free amino acids and small peptides was designed as a positive control diet. There was no significant difference in the growth and feed utilization among three dipeptide diets (Lys-Leu, Lys-Gly, and Gly-Leu). Compared with the CAA group, feed efficiency ratio was significantly higher in the Lys-Leu and Lys-Gly groups, and protein efficiency ratio was significantly higher in the Lys-Leu group. For peptide transporter, oligopeptide transporter 1 (PepT1) mRNA level was not affected by dietary treatments. For amino acid transporters, lower expression of B0 neutral amino acid transporter 1 (B0AT1) and proton-coupled amino acid transporter 1 (PAT1) were observed in fish fed the dipeptide and FPH diets compared with the CAA diet. In conclusion, juvenile turbot fed Lys-Leu, Gly-Leu, and Lys-Gly had a similar growth performance, whereas lysine and leucine in the Lys-Leu form can be utilized more efficiently for feed utilization than those in free amino acid from. In addition, compared to free amino acids, dipeptides and fish protein hydrolysate in diets may down-regulate the expression of amino acid transporters but did not affect the expression of PepT1.

A feeding trial was conducted to test the efficacy of the fish oil-finishing strategy in a lean marine teleost, tiger puffer (average initial body weight, 19.50 g). During the 50-day growing-out period, fish was fed diets differing only in supplemented lipid source (6% of dry dietary matter), namely, fish oil (FO), tiger puffer liver oil (TO), linseed oil (LO), soybean oil (SO), rapeseed oil (RO), palm oil (PO), and beef tallow (BT). In the fish oil-fishing period, all the fish were fed diet FO for 30 days. The results showed that the fish oil-finishing strategy restored the muscle DHA content in terrestrially sourced oil (TSO)-based groups to be 82.8–91.6% of that in fish fed fish oil continuously. Compared to DHA, muscle EPA was less easily retained during the growing-out period, but more easily restored during the fish oil-finishing period. Compared to muscle, the LC-PUFA contents in liver of tiger puffer were much lower and more difficult to restore by the fish oil-finishing strategy. LO, RO and BT resulted in significant growth reduction than FO at the end of growing-out period, but this reduction no longer existed at the end of the fish oil-finishing period. Compensatory effects of fish oil re-feeding were also observed for LC-PUFA deposition. Very little difference was observed in fish proximate composition, somatic parameters, and muscle texture among dietary groups during the whole feeding period, but the lipid metabolism-related biochemical parameters in the serum were significantly affected by diet. Liver oil of farmed tiger puffer can be used a suitable and safe lipid source for diets of tiger puffer, and beef tallow seems a better dietary lipid source for tiger puffer than other TSO in terms of easy restoration of LC-PUFA and growth by the fish oil-finishing strategy. In conclusion, the fish oil-finishing strategy had high efficiency in restoring LC-PUFA and growth of tiger puffer previously fed TSO-based diets.

This study aimed to determine the dietary arginine requirement of tiger puffer (Takifugu rubripes), and to assess the effect of dietary arginine levels on intestinal peptide and amino acid transporters, and target of rapamycin (TOR) signaling pathway in muscle. Six experimental diets were formulated to contain 480 g kg−1 crude protein from fishmeal, corn protein concentrate and crystalline amino acid premix with graded levels of arginine (19.1, 21.5, 24.4, 26.7, 30.0 and 32.5 g kg−1 of dry diet). Each diet was randomly fed to triplicate groups of 25 fish (an average initial body weight of 19.97 g) per tank. Final body weight, specific growth rate (SGR), feed efficiency ratio, protein efficiency ratio and protein productive value increased with the increase of dietary arginine levels from 19.1 to 24.4 g kg−1 (p 0.05). In conclusion, an optimal level of dietary arginine stimulated intestinal peptide and amino acid transporters, while gene expressions of TOR signaling pathway in muscle were not responsive to dietary arginine levels. Based on nonlinear regression analysis of SGR, the dietary arginine requirement of tiger puffer was estimated to be 24.40 g kg−1 of dry diet (50.12 g kg−1 of dietary protein).

Use of terrestrially sourced oil (TSO) in fish diets easily causes adverse effects on fillet quality. The present study, with turbot, was aimed at evaluating the efficacy of alternate feeding between fish oil (FO)- and TSO-based diets in minimizing these adverse effects. The control group were fed the FO-based diet continuously for 13 weeks, meanwhile other groups were subjected to weekly alternation between the FO-based diet and diets based on TSO, namely, linseed oil, soybean oil, rapeseed oil, palm oil, and beef tallow, respectively. The feeding trial was conducted in a flow-through seawater system. Each group had triplicate tanks, and each tank was stocked with 35 fish. Samples were collected at the end of Week 9 and 13. At Week 9, no significant difference among groups was observed in growth performance and muscle proximate composition, texture, and odour-active compound profile; however significant differences were observed in muscle content of long-chain polyunsaturated fatty acids, serum malondialdehyde content, and somatic indices. These differences disappeared at Week 13. In conclusion, long-term alternation between FO- and TSO-based diets could mitigate the adverse effects of TSO on farmed turbot.

A 1H NMR-based metabolomics approach was to explore the effect of ultrafiltered fish protein hydrolysate (UF) levels on the liver and muscle metabolic profile of juvenile turbot (Scophthalmus maximus L.). Fish protein hydrolysate (FPH) was produced from by-products by enzymatic treatment, and UF was obtained by diluting FPH followed filtration. Fish were fed diets containing fish meal protein, which was, respectively, replaced by UF protein 0, 50, 100, 150 and 200 g kg−1 of dietary total protein (UF-0, UF-5, UF-10, UF-15 and UF-20) for 68 days. OPLS-DA of liver and muscle showed that high levels of UF in diets may lead to corresponding tissue metabolites changes. In liver tissue, changing metabolites included dimethylamine, N,N-dimethylglycine, valine, isoleucine, leucine, arginine and alanine and were mainly involved in choline metabolism and amino acid metabolism. For muscle tissue, changing metabolites included lactate, alanine, proline, fumarate, tyrosine, histidine, cystathionine and taurine. And the metabolites were mainly involved in glycolysis and gluconeogenesis, proline metabolism and taurine metabolism. 1H NMR-based metabolomics is a useful approach to investigate different levels of UF on metabolic profile in liver and muscle tissues combined with the growth.

A 10-week feeding experiment was conducted to investigate the effects of different types of dietary protein hydrolysate (PH) on growth performance, body composition, trypsin activity and serum transaminase of juvenile turbot. Four high plant protein diets contained different types of PH, fish PH (FPH), yeast PH (YPH), pig blood PH (PBPH) and soy PH (SPH), replacing 10% fishmeal of the basal diet. The basal diet with 30% fishmeal and no PH was used as the control diet (C). Each diet was assigned to triplicate groups of 30 fish. The specific growth rate (SGR) was not significantly different between groups C and FPH, but groups C and FPH showed significantly higher SGR than other groups. The feed efficiency ratio (FER) and protein efficiency ratio (PER) were not significantly different among groups C, FPH and YPH, but groups PBPH and SPH showed significantly lower FER and PER than groups C and FPH. Group PBPH showed significantly higher hepatosomatic index than other groups except YPH. Fish fed YPH showed significantly lower whole-body protein content, but significantly higher whole-body lipid content than fish fed diets C, FPH and PBPH. The activities of serum GOT and GPT in group PBPH were higher than those in groups C, FPH and YPH. These results suggested that when used at a low level in high plant protein diets for juvenile turbot, FPH is a good alternative protein source and YPH also has the application potential, but PBPH and SPH can cause negative impacts on fish growth and health.

This study was designed to evaluate changes in the metabolic profile of liver and muscle of turbot (Scophthalmus maximus L.) fed fishmeal-based diet, diets containing size-fractionated fish protein hydrolysate and plant protein-based diet using 1H NMR-based metabolomics approach combined with the growth. Fish protein hydrolysate (FPH) was obtained by enzymatic treatment, permeate fraction was obtained as UF by ultrafiltered step, and retentate fraction was retained as RF. FM diet contained fish meal used as a single protein source. Four other diets (PP, UF, FPH and RF) contained 180 g kg−1 diet fish meal. 54, 55 and 55 g kg−1 dry diet UF, FPH and RF were supplemented to UF, FPH and RF diets. All diets were formulated to be isolipidic and isonitrogenous fed to five triplicate groups of turbot (16.05 ± 0.03 g) for 68 days. O-PLS-DA in FM versus UF, FM versus FPH, FM versus RF and FM versus PP resulted in a reliable model for muscle and liver tissue, while O-PLS-DA in UF versus FPH and UF versus RF only showed metabolites changes in liver tissue. Results indicated that metabolite changes among the different treatments were consistent with the growth tendency.

A 12-week feeding experiment in indoor flowing seawater system was conducted to investigate the effects of graded levels of dietary fish protein hydrolysate (FPH) on growth performance and lipid accumulation of juvenile turbot ( Scophthalmus maximus ) (initial body weight 4.16 ± 0.01 g). Four isonitrogenous and isoenergetic experimental diets with high plant protein were formulated to contain graded levels of FPH, meanwhile the fish meal was replaced correspondingly by 0% (Diet FPH-0, control), 5% (Diet FPH-5), 10% (Diet FPH-10) and 20% (Diet FPH-20) of total dietary protein, respectively. Quadruplicate groups of 25 fish were fed to apparent satiation twice daily during the feeding trial. The results showed that the specific growth rate (SGR), protein efficiency ratio, and protein retention was not significantly different among group FPH-0, FPH-5, and FPH-10. The highest level of dietary FPH (FPH-20) significantly reduced the SGR but increased the feed intake compared to the control group. The viscerosomatic index in group FPH-10 and FPH-20 were significantly lower than that in the control group. Fish fed FPH-20 also showed significantly lower crude lipid concentration in whole body than fish fed the control diet. The concentrations of total and neutral lipid in gut were significantly lower in fish fed FPH-10 compared to the control group. For muscle lipid, the polar lipid concentration significantly decreased while the neutral lipid concentration significantly increased with increasing levels of dietary FPH, but no significant difference in total lipid concentration was observed among experimental groups. The lipid concentrations in liver were not significantly different among dietary treatments. With increasing levels of dietary FPH, serum triacylglycerol and cholesterol concentrations significantly decreased. The influence of dietary FPH on tissue fatty acid compositions generally corresponded with that on tissue lipid concentrations. In conclusion, these results suggested that in high plant protein diets FPH replacing fish meal by 10% of total dietary protein did not compromise the growth of juvenile turbot. However, a higher FPH level (replacing fish meal by 20% of total dietary protein) reduced the growth and feed utilization but it increased the feed intake. In the present experimental conditions, the FPH treatments, especially at high levels, significantly modulated the lipid accumulation and fatty acid compositions in turbot tissues, in a dose- and tissue-dependent manner. Statement of Relevance This study provided useful data for the circulatory use of fish processing by-products in fish diets. Also, based on the results of lipid analysis in fish tissues, potential lipid manipulating feed additives could be explored from fish protein hydrolysates.

An eight week feeding trial was conducted to investigate the effect of taurine supplementation on growth performance, sulfur amino acid concentrations, the activity and gene expression of enzymes related to taurine synthesis, and gene expression of taurine transporter (TAUT) in tiger puffer (Takifugu rubripes). Test diets were respectively supplemented with 0, 3, 6, 9, 12 and 20 g kg−1 taurine (the T0, T3, T6, T9, T12 and T20 diets) and a control diet was supplemented with 12 g kg−1 cysteine (the Cys diet). All experimental diets were fed to triplicate groups of 25 fish (initial weight 20.05 ± 0.06 g). Dose responses were observed in terms of specific growth rate and feed efficiency ratio. Dietary taurine requirement was estimated at 5.25 and 8.23 g kg−1 of dry matter of the diet based on regression analysis for specific growth rate and feed efficiency ratio, respectively. Free taurine concentrations of muscle and liver tissues increased with the increase of dietary taurine concentration. However, there was no significant difference in free taurine concentrations in muscle or liver between the Cys and T0 groups (p > .05). Free methionine concentration of liver tissue gradually increased with the increase of dietary taurine, which implied that exogenous taurine appeared to spare hepatic methionine. Cysteine sulfinic acid decarboxylase (CSD) activity and mRNA level in liver were down-regulated in the T9, T12 and T20 groups compared with the T0 group (p .05). TAUT mRNA levels in muscle had a decrease trend in fish fed diets containing 1.7 to 8.2 g kg−1 taurine (the T0, T3 and T6 groups), while there was no significant difference when dietary taurine concentrations increased from 8.2 to 21.9 g kg−1 (the T6, T9, T12 and T20 groups). In conclusion, tiger puffer cannot synthesize taurine in the liver at the level of cysteine used in this study, whereas a sparing effect on the methionine demand may be observed in liver by dietary taurine supplementation. Our data indicates that taurine is a conditionally essential amino acid for tiger puffer, and the taurine requirement was estimated ranged from 5.25 to 8.23 g kg−1 of dry matter of the diet.

Methionine (Met) is one of the most important amino acids in fish feed. The effects of dietary Met on lipid deposition in fish varied a lot among different studies. The present study was aimed at investigating the effects of dietary Met supplementation on the lipid accumulation in tiger puffer, which have a unique lipid storage pattern. Crystalline L-Met was supplemented to a low-fishmeal control diet to obtain two experimental diets with a low (1.1% of dry weight, L-MET) or high Met level (1.6% of dry weight, H-MET). A 67-day feeding trial was conducted with juvenile tiger puffer (average initial weight, 13.83 g). Each diet was fed to triplicate tanks (30 fish in each tank). The results showed that the total lipid contents in whole-body and liver significantly increased with increasing dietary Met levels. The hepatosomatic index, weight gain, and total bile acid content in serum showed similar patterns in response to dietary Met treatments, while the lipid content in muscle was not affected. The hepatic contents of 18-carbon fatty acids were elevated by dietary Met supplementation. The Hepatic mRNA expression of lipogenetic gene such as FAS, GPAT, PPARγ, ACLY, and SCD1 was down-regulated, while the gene expression of lipolytic genes ACOX1 and HSL, as well as that of ApoB100, were up-regulated by increasing dietary Met levels. The hepatic lipidomics of experimental fish was also analyzed. In conclusion, increasing dietary Met levels (0.61%, 1.10%, and 1.60%) increased the hepatic lipid accumulation in tiger puffer. The mechanisms involved warrant further studies.

The intention of the study was to investigate the effect of ultrafiltered fish protein hydrolysate (UF) level on growth, feed utilization, apparent digestibility coefficients and proximal intestine peptide transporter 1 (PepT1) mRNA level for juvenile turbot (Scophthalmus maximus L.). Experimental diets (UF-0, UF-5, UF-10, UF-15 and UF-20) were prepared containing about 68% plant protein, and fish meal protein was, respectively, replaced by 0%, 5%, 10%, 15% and 20% UF of dietary protein. Diet PP contained about 78% plant protein, and diet CAA contained about 10% crystalline amino acid mixture. All diets were fed to seven triplicate groups of turbot (initial weight 16.05 ± 0.03 g) for 68 days. Fish fed diet UF-10 had an increasing tendency in growth compared with diets contained UF, while dietary UF level was not significantly correlated with specific growth rate and feed intake. Feed efficiency, protein efficiency ratio and protein productive value significantly correlated with dietary UF level, and fish fed diets contained low-level UF had higher digestibility than that diets UF-0, PP and CAA. There was a decreasing tendency in PepT1 expression level with dietary UF level. The results indicated that low-level UF showed a positive effect on growth and feed utilization in juvenile turbot.

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, 17α-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.