Marine Fish Oil Replacement with Lard or Basa Fish (Pangasius bocourti) Offal Oil in the Diet of Tiger Puffer (Takifugu rubripes): Effects on Growth Performance, Body Composition, and Flesh Quality.

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.

Combined Replacement of Fishmeal and Fish Oil by Poultry Byproduct Meal and Mixed Oil: Effects on the Growth Performance, Body Composition, and Muscle Quality of Tiger Puffer.

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.

Exposure of farmed fish to petroleum hydrocarbon pollution and the recovery process: A simulation experiment with tiger puffer Takifugu rubripes.

Petroleum hydrocarbon (PH) pollution threatens both wild and farmed marine fish. How this pollution affects the nutrient metabolism in fish and whether this effect can be recovered have not been well-known. The present study aimed to evaluate these effects with a feeding trial on tiger puffer, an important farmed species in Asia. In a 6-week feeding trial conducted in indoor flow-through water, fish were fed a control diet (C) or diets supplemented with diesel oil (0.02 % and 0.2 % of dry matter, named LD and HD, respectively). Following this feeding trial was a 4-week recovery period, during which all fish were fed a same normal commercial feed. At the end of the 6-week feeding trial, dietary PH significantly decreased the fish growth and lipid content. The PH significantly accumulated in fish tissues, in particular the liver, and caused damages in all tissues examined in terms of histology, anti-oxidation status, and serum biochemical changes. Dietary PH also changed the volatile flavor compound profile in the muscle. The hepatic transcriptome assay showed that the HD diet tended to inhibit the DNA replication, cell cycle and lipid synthesis, but to stimulate the transcription of genes related to liver protection/repair and lipid catabolism. The 4-week recovery period to some extent mitigated the damage caused by PH. After the recovery period, the inter-group differences in some parameters disappeared. However, the differences in lipid content, anti-oxidase activity, liver PH concentration, and histological structure still existed. In addition, differences in cellular chemical homeostasis and cytokine-cytokine receptor interaction at the transcriptional level can still be observed, indicated by the hepatic transcriptome assay. In conclusion, 6 weeks of dietary PH exposure significantly impaired the growth performance and health status of farmed tiger puffer, and a short-term recovery period (4 weeks) was not sufficient to completely mitigate this impairment.

Effects of acute hypoxia on nutrient metabolism and physiological function in turbot, Scophthalmus maximus.

Acute hypoxia is a common stress in aquaculture, and causes energy deficiency, oxidative damage and death in fish. Many studies have confirmed that acute hypoxia activated hif1α expression, anaerobic glycolysis and antioxidant system in fish, but the effects of acute hypoxia on lipid and protein metabolism, organelle damage, and the functions of hif2α and hif3α in economic fishes have not been well evaluated. In the present study, turbot was exposed to acute hypoxia (2.0 ± 0.5 mg/L) for 6 h, 12 h, and 24 h, respectively. Then, the contents of hemoglobin (HB), metabolite, gene expressions of hifα isoforms, energy homeostasis, endoplasmic reticulum (ER) stress, and apoptosis were measured. The results suggested that turbot is intolerant to acute hypoxia and the asphyxiation point is about 1.5 mg/L. Acute hypoxia induced perk-mediated ER stress, and increased lipid peroxidation and liver injury in turbot. The blood HB level and liver vegfab expression were increased under hypoxia, which enhances oxygen transport. At hypoxia stress, hif3α, anaerobic glycolysis-related genes expression, and lactate content were increased in the liver, and glycogen was broken down to ensure ATP supply. Meanwhile, hif2α, lipid synthesis-related genes expression, and TG content were increased in the liver, but the lipid catabolism and protein synthesis were suppressed during hypoxia, which reduced the oxygen consumption and ROS generation. Our results systematically illustrate the metabolic and physiological changes under acute hypoxia in turbot, and provide important guidance to improve hypoxia tolerance in fish.

Feeding Strategy to Use Beef Tallow and Modify Farmed Tiger Puffer Fatty Acid Composition.

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.

Growth, Cannibalism, and 5-TH Metabolism in Pufferfish (Takifugu obscurus ♀ × Takifugu rubripes): The Role of Graded Levels of Dietary Tryptophan.

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.

Dietary Cholesterol Supplementation Inhibits the Steroid Biosynthesis but Does Not Affect the Cholesterol Transport in Two Marine Teleosts: A Hepatic Transcriptome Study.

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.

Short-Term Alternate Feeding between Terrestrially Sourced Oil- and Fish Oil-Based Diets Modulates the Intestinal Microecology of Juvenile Turbot.

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.

Dietary Cholesterol Differentially Regulates the Muscle Lipidomics of Farmed Turbot and Tiger Puffer.

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.

Recovery of Fatty Acid and Volatile Flavor Compound Composition in Farmed Tiger Puffer (Takifugu rubripes) with a Fish Oil-Finishing Strategy.

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.

Response of Intestinal Microbiota of Tiger Puffer (Takifugu rubripes) to the Fish Oil Finishing Strategy.

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-1ß, TNF-α, TGF-ß) 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.

Effects of Lysophosphatidylcholine on Intestinal Health of Turbot Fed High-Lipid Diets.

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-1ß, 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.

Sex difference in fatty acid composition of six marine teleosts.

This study investigated the sex difference in fatty acid (FA) composition of six wild marine fish species, namely, Cleisthenes herzensteini, Platichthys bicoloratus, Pseudosciaena polyactics, Platycephalus indicus, Alosa sapidissima and Scomberomorus niphonius. The coefficient of distance value between sexes (Dsex ) and multi-variate similarity of percentages analysis (SIMPER) revealed universal existence of sex difference in FA composition, particularly in gonad, intestine and liver. Nonetheless, this sex difference was highly dependent on fish species. In general, DHA, 18:1n-9, 16:1n-7, 16:0 and EPA appeared to be the TOP FAs differentially abundant between sexes.

Additional supplementation of sulfur-containing amino acids in the diets improves the intestinal health of turbot fed high-lipid diets.

An eight-week feeding trial was conducted to investigate the effects of diets supplemented with three sulfur-containing amino acids (SAA), namely, methionine, cysteine, and taurine, on the intestinal health status of juvenile turbot (Scophthalmus maximus) fed high-lipid diets. Four diets were formulated, namely, a high-lipid control diet (16% lipid, HL) and three SAA-supplemented diets, which were formulated by supplementing 1.5% methionine (HLM), 1.5% cysteine (HLC), and 1.5% taurine (HLT) into the HL control diet, respectively. Each diet was assigned to triplicate tanks, and each tank was stocked with 30 juvenile fish (appr. initial weight, 8 g). The histological and morphometric results showed that dietary SAA supplementation obviously improved the intestinal morphology and integrity, in particular as reflected by higher height of microvilli and mucosal folds. Dietary SAA supplementation, in particular cysteine, up-regulated the gene expression of mucin-2 and tight junction proteins (ZO-1, Tricellilun and JAM). Dietary SAA supplementation remarkably down-regulated the gene expression of apoptosis-related factors such as p38, JNK, and Bax, expression of pro-inflammatory factors (e.g., NF-κB, AP-1 IL-1ß, IL-8, and TNF-α). SAA supplementation resulted in higher antioxidative abilities in the intestine. Additionally, dietary SAA supplementation largely altered the communities of intestinal microbiota. Compared with the HL group, higher relative abundance of potential beneficial bacteria, and lower relative abundance of opportunistic pathogens were observed in SAA-supplemented groups. Dietary taurine supplementation significantly increased the relative abundance of Ligilactobacillus (in particular Lactobacillus murinus) and Limosilactobacillus (especially Lactobacillus reuteri). In conclusion, dietary sulfur-containing amino acids supplementation have promising potential in ameliorating the intestinal inflammation of turbot fed high-lipid diets. Especially dietary cysteine and taurine supplementation have more positive effects on the communities of the intestinal microbiota of turbot.

Dietary lysophosphatidylcholine regulates diacylglycerol, cardiolipin and free fatty acid contents in the fillet of turbot.

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.

Response of lipid and fatty acid composition of turbot to starvation under different dietary lipid levels in the previous feeding period.

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.

Dietary lipid levels affected antioxidative status, inflammation response, apoptosis and microbial community in the intestine of juvenile turbot (Scophthalmus maximus L.).

A nine-week feeding trial was conducted to comprehensively investigate the effects of different levels of dietary lipid on intestinal physiology of juvenile turbot. Three diets with different lipid levels (8%, 12% and 16%) were formulated, which were designated as the low-lipid group (LL), medium-lipid group (ML) and high-lipid group (HL), respectively. Each diet was fed to six replicate tanks, and each tank was stocked with 35 fish. The results revealed that medium dietary lipid (12%) increased the activities of intestinal digestive enzymes and brush border enzymes. Excessive dietary lipid (16%) decreased the intestinal antioxidative enzyme levels and increased the lipid peroxidation pressure. In addition, HL stimulated the occurrence of intestinal inflammation and significantly up-regulated the mRNA expression level of tumor necrosis factor-α (TNF-α), interleukin-1ß (IL-1ß), interferon-γ (IFN-γ) and transforming growth factor-ß (TGF-ß). Dietary LL and HL induced the apoptosis of intestinal epithelial cells. Sequencing of bacterial 16 s rRNA V4 region indicated that the abundance and diversity of intestinal microflora in fish fed with medium lipid diet (12%) were significantly higher than those in other groups, indicating the intestinal microflora ecology in group ML was more balanced. MetaStat analysis indicated that both low- and high-lipid diets significantly reduced the relative abundance of intestinal beneficial bacteria. In conclusion, results of this study demonstrated the sensitivity of intestinal health and microbiota to dietary lipid levels. From the perspective of microecological balance, medium dietary lipid (12%) was more conducive to maintaining the intestinal microflora stability of turbot.

Fish Oil Replacement with Poultry Oil in the Diet of Tiger Puffer (Takifugu rubripes): Effects on Growth Performance, Body Composition, and Lipid Metabolism.

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.

Screening of reference genes in tiger puffer (Takifugu rubripes) across tissues and under different nutritional conditions.

The present study was aimed at screening suitable reference genes for quantitative real-time polymerase chain reaction (qRT-PCR) in tiger puffer (Takifugu rubripes), an important aquaculture species in Asia and also a good model species for lipid research. Specifically, this reference gene screening was targeted at standardization of gene expression in different tissues (liver, muscle, brain, intestine, heart, eye, skin, and spleen) or under different nutritional conditions (starvation and different dietary lipid levels). Eight candidate reference genes (ribosomal protein L19 and L13 (RPL19 and RPL13), elongation factor-1 alpha (EF1α), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), hypoxanthine guanine phosphoribosyl transferase1 (HPRT1), beta-2-Microglobulin (B2M), 18S ribosomal RNA (18SrRNA), and beta actin (ACTB)) were evaluated with four algorithms (geNorm, NormFinder, BestKeeper, and comparative ΔCt method). The results showed that different algorithms generated inconsistent results. Based on these findings, RPL19, EF1α, 18SrRNA, and RPL13 were relatively stable in different tissues of tiger puffer. During starvation conditions, ACTB/RPL19 was the best reference gene combination. Under different dietary lipid levels, ACTB/RPL13 was the most suitable reference gene combination. The present results will help researchers to obtain more accurate results in future qRT-PCR analysis in tiger puffer.

Are fish what they eat? A fatty acid's perspective.

Fish are the main source of long-chain polyunsaturated fatty acids (LC-PUFA, >C18) 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.