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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.

This study was conducted to elucidate the effects of oxidised dietary lipids and high-dose vitamin E (VE) on growth performance and immune responses of large yellow croaker. Juvenile fish (initial average body weight of 7·82 (sem 0·68) g) were fed diets containing either fresh fish oil (fresh diet, peroxide value (POV)=1·72 mEq/kg) or fish oil oxidised to varying degrees (oxidised diets, POV=28·29-104·21 mEq/kg), with or without supplementary 600 mg VE/kg diet, for 10 weeks in floating cages. Growth was significantly lower and feed intake (g/100 g body weight per d) was higher in fish fed the oxidised diet. Supplementation with VE increased the growth of fish fed the oxidised diets, but significantly decreased the growth of fish fed the fresh diet. Hepatosomatic index increased with increasing dietary POV and decreased with VE supplementation. Hepatic catalase activity, superoxide dismutase (SOD) activity and malondialdehyde content were significantly higher in fish fed the oxidised diets, and these values decreased significantly following VE supplementation. However, hepatic SOD activity was enhanced by VE supplementation in fish fed the fresh diet. Air-exposure mortality was significantly increased by dietary POV, and this effect was inhibited by VE supplementation. These results suggest that dietary oxidised fish oil could stimulate the activities of antioxidant defence enzymes in stressed large yellow croaker. High-dose VE supplementation can alleviate oxidative stress of large yellow croaker fed oxidised fish oil, but can exert deleterious effects on fish in the absence of oxidative stress.

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. [ABSTRACT FROM AUTHOR]

Aquaculture has become the largest source of seafood consumption, leading to increased research in aqua-nutrition. A survey of publications on aqua-nutrition topics was conducted, revealing that feed additives are the most studied area due to the need for alternatives to antibiotics. Plant extracts and microbial agents are popular feed additives, with a focus on natural and green options. Research on alternative protein and lipid sources, such as insects and microalgae, is also prominent. The study emphasizes the importance of considering the demands of the aquaculture industry and market in aqua-nutrition research. [Extracted from the article]

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. [ABSTRACT FROM AUTHOR]

Simple Summary: The supply of fish oil, which provides long-chain polyunsaturated fatty acids (LC-PUFA) but is mostly wild-caught, is stagnating, resulting in limited availability and high prices. Therefore, many alternative lipid sources, mainly vegetable oils and rendered animal fats, are increasingly being applied in fish feeds. However, these lipid sources do not contain LC-PUFA, and therefore lower the fillet quality in terms of the LC-PUFA content. Feeding strategies such as alternate feeding between fish oil- and alternative oils-based diets have been applied to maintain the n-3 LC-PUFA contents in farmed fish. The present study validated the relevant efficacy. 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Use of terrestrially sourced oils (TSO) in the diet easily causes reduction in long‐chain polyunsaturated fatty acids (LC‐PUFA) in farmed fish. Alternate feeding between fish oil (FO)‐ and TSO‐based diets is a potential strategy for mitigating this LC‐PUFA reduction. The present study, with turbot, was aimed at comparing the fatty acid‐regulating effects of the alternate‐feeding strategy in different tissue types, namely, muscle, liver and subcutaneous tissue around the fin (STF). 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. Each dietary group had triplicate tanks, and each tank was stocked with 35 fish. Tissue samples were collected at the end of Week 9 and 13. At Week 9, significant differences among dietary groups were observed in LC‐PUFA contents of all tissue types; at Week 13, the significant difference in muscle disappeared, but those in liver and STF remained. STF seemed more like a lipid storage site, with high contents of 18:1n‐9 and 18:3n‐3, but low LC‐PUFA contents. Among all the treatments, alternate feeding between FO‐ and beef tallow‐based diets resulted in the most similar fatty acid profile to the treatment with continuous FO feeding. This study added knowledge to the fatty acid composition of fish subcutaneous tissue, as well as to promising application of beef tallow in fish feed. [ABSTRACT FROM AUTHOR]

A 66-d feeding experiment was conducted to investigate the utilization of vegetable oils in Japanese seabass (initial weight: 10.09 ± 0.70 g). In experimental diets, linseed oil ( LO) or soybean oil ( SO) was used to replace 1/3, 2/3, and 3/3 of fish oil ( FO) (Diets F2L1, F1L2, and LO, respectively, or Diets F2S1, F1S2, and SO, respectively). A diet with FO alone was used as the control diet. LO or SO supplementation did not reduce the specific growth rate (3.06-3.29%/d) and feed efficiency ratio (0.75-0.83) of fish, but group F2L1 showed significantly better growth ( P < 0.05) and feed utilization ( P < 0.01) than group SO. Total replacement of FO with LO or SO significantly reduced certain non-specific innate immune responses. Total replacement of FO by LO significantly increased the lipid content of fish. Concentrations of long-chain polyunsaturated fatty acids ( LC-PUFAs) in whole fish and tissues were significantly reduced by LO or SO supplementation. In conclusion, LO or SO supplementations did not reduce the growth of Japanese seabass but reduced the immune responses and LC-PUFA concentrations. LO was a better lipid source than SO for Japanese seabass in terms of fish growth and immune responses. [ABSTRACT FROM AUTHOR]

[Display omitted] • Starvation and high dietary lipid synergistically increased the muscle lipid. • Starvation mobilized different fatty acids among different tissues of turbot. • The subcutaneous tissue around the fin appears to be a pure lipid storage site. • Starvation affected some muscle texture parameters in a time-dependent manner. • Combined use of starvation and dietary lipid change well regulates fillet quality. The present study was aimed at investigating the interactive effects of starvation and dietary lipid level in the previous feeding period on lipid-related composition of turbot. Turbot with an average initial body weight of 26 g were firstly fed diets with different lipid levels, namely, 8%, 12%, and 16%, for 9 weeks, and then subjected to starvation for 30 days. Each diet was fed to sextuplicate tanks of 35 fish in the feeding trial. Tissue samples were collected at the end of the feeding trial and at 10, 20, and 30 days after starvation. The results showed that 30-day starvation decreased the lipid content in the liver and the subcutaneous tissue around the fin (STF), but increased the lipid content in the muscle. A synergetic increase of muscle lipid by starvation and dietary lipid level was observed. Starvation mobilized different fatty acids among the three tissues, namely, MUFA (16:1n-7 and 18:1n-9) in the muscle, SFA (14:0 and 16:0), MUFA (16:1n-7, 18:1n-9 and 20:1n-9), and 18C-PUFA (18:2n-6 and 18:3n-3) in the liver, and unexpectedly n-3 PUFA (18:3n-3, EPA, and DHA) in the STF, respectively. The 30-day starvation decreased the muscle hardness and resilience, but affected other texture parameters in a starvation time-dependent manner. Up-regulation of expression of lipolytic genes by starvation occurred later in the STF than in the liver. Interactive effects of starvation and dietary lipid level were observed mainly on tissue fatty acid compositions. Results of this study suggested that combined manipulation of starvation time and dietary lipid level could be used as an effective means of fish quality regulation in terms of lipid/fatty acid-related composition. [ABSTRACT FROM AUTHOR]

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. Unlabelled Image • Terrestrially sourced oil (TSO) in fish diets easily causes adverse effects. • Alternate feeding between fish oil and TSO prevented changes in growth. • Alternate feeding prevented changes in muscle texture and odour-active compounds. • Long-term alternate feeding prevented changes in muscle LC-PUFA. [ABSTRACT FROM AUTHOR]

Fish are the main source of long-chain polyunsaturated fatty acids (LC-PUFA, >C 18) for human consumption. In general, it has been widely observed that the fatty acid (FA) profiles of farmed fish are reflective of the diet. However, the degree of tissue FA "distortion" based on incorporation of different dietary FA into fish tissues varies greatly depending on FA type, fish species and environmental factors. In terms of fish FA composition, this variation has not been comprehensively reviewed, raising the question: "Are fish what they eat?". To date, this remains unanswered in detail. To this end, the present review quantitatively summarized the 'diet-fish' FA relationship via an analysis of FA composition in diets and fish tissues from 290 articles published between 1998 and 2018. Comparison of this relationship among different fish species, tissue types or individual FA was summarized. Furthermore, the influence of environmental factors such as temperature and salinity, as well as of experimental conditions such as fish size and trophic level, feeding duration, and dietary lipid level on this relationship are discussed herein. Moreover, as a means of restoring LC-PUFA in fish, an emphasis was paid to the fish oil finishing strategy after long-term feeding with alternative lipid sources. It is envisaged that the present review will be beneficial in providing a more comprehensive understanding of the fundamental relationship between the FA composition in diets, and subsequently, in the farmed fish. Such information is integral to maintaining the quality of farmed fish fillets from the perspective of FA composition. • The 'diet-fish' FA relationship was systematically reviewed. • The 'diet-fish' FA relationship was analyzed by quantitative approaches. • Factors influencing the 'diet-fish' FA relationship were analyzed and discussed. • An emphasis was paid to the fish oil finishing strategy in fish farming. • Dietary FA incorporation in fish tissues is affected by many non-dietary factors. [ABSTRACT FROM AUTHOR]

A 12-week feeding trial was conducted to evaluate the effects of dietary fish oil (FO) replacement by beef tallow (BT) on the growth performance and body composition of juvenile turbot (average initial weight, 19.6 g). The control diet contained 6% added FO (of dry matter, Diet FO-C). Beef tallow was supplemented into Diet FO-C, replacing added FO at different levels, i.e., 25%, 50%, 75%, and 100%, formulating the other 4 experimental diets, designated as 25BT, 50BT, 75BT, and 100BT, respectively. The feeding trial was conducted in a flow-through seawater system. Each diet was randomly fed to triplicate tanks (30 fish in each tank). The results showed that a cubic regression relationship was observed between weight gain and dietary FO replacement level. Although total FO replacement by BT significantly reduced the growth of juvenile turbot, no significant difference was observed between FO-C and 75BT. Diet BT decreased the whole-body crude lipid content but increased the whole-body moisture and ash contents. Dietary BT regulated the proximate composition of fish tissues in a dose dependent manner. High dietary BT levels did not reduce the n-3 long-chain polyunsaturated fatty acid content (% total fatty acid) in the muscle. Partial FO replacement (25 and 50%) by BT even significantly increased the muscle DHA content. The fatty acid composition of the liver, subcutaneous adipose tissue around the fin, and intestine generally reflected those of the diets. No significant difference was observed in muscle and liver mitochondrial DNA copy number among groups, indicating the similar general energy supply status. Dietary BT significantly reduced the concentration of triacylglycerol, cholesterol and malondialdehyde in the serum. The volatile flavor compound in muscle was analyzed with gas chromatography-ion migration spectrometry (GC-IMS). Dietary BT resulted in lower number and abundance of flavor aldehydes and alcohols in the muscle. In conclusion, beef tallow can replace 75% added fish oil (appr. 45% of total fish oil including the residual fish oil in fishmeal) in the diets of turbot, without reducing fish growth. Dietary beef tallow significantly affected the body composition and volatile flavor compound composition in the muscle. • Beef tallow can replace 75% added fish oil in turbot diets. • Partial fish oil replacement by beef tallow increased the muscle DHA content. • Dietary beef tallow resulted in lower abundance of flavor aldehydes and alcohols. • Dietary beef tallow decreased the whole-body crude lipid content. [ABSTRACT FROM AUTHOR]

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. • DHA was easily retained in muscle of tiger puffer fed terrestrial oils. • The fish oil-finishing had high efficiency in restoring LC-PUFA in tiger puffer. • Compensatory effects of fish oil-finishing existed for both LC-PUFA and growth. • Liver oil of tiger puffer and beef tallow are good lipid sources for tiger puffer. • Fish proximate composition and muscle texture were not affected by dietary oils. [ABSTRACT FROM AUTHOR]