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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.

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

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.

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.

An 8-week feeding trial was conducted to comprehensively investigate the effects of dietary phosphorus level and stocking density on tiger puffer. A 3 × 3 factorial design was used. The three dietary phosphorus levels were 0.68% (LP), 0.98% (MP), and 1.31% (HP) of dry matter, of which the available phosphorus level was 0.44%, 0.76%, and 1.06%, respectively. The three stocking density grades were 1.53 (LD), 2.30 (MD), and 3.06 (HD) kg m−3. The feeding trial was conducted in an indoor flow-through seawater system. Three replicate tanks were used for each group. The results showed that HP resulted in the highest growth rate. Higher dietary phosphorus levels reduced the whole-body lipid content, serum cholesterol contents, and hepatic mRNA expression of lipid metabolism-related genes such as ACACβ, DGAT1, and PPARα2. High stocking density levels reduced the growth rate and feed intake, but rarely affected other physiological parameters. Significant interactions were observed between effects of dietary phosphorus level and stocking density on phosphorus and calcium metabolism, but not between effects of both variables on the growth performance. Synergetic enhancement of phosphorus excretion by high phosphorus level and high stocking density was observed. These results shed new lights into the phosphorus physiology of marine fish and the interactions between phosphorus nutrition and rearing condition.

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

Bile acid (BA) plays an important role in lipid metabolism. Tiger puffer has a unique lipid storage pattern; storing lipid predominantly in the liver. The present study aimed to investigate the effects of dietary BA supplementation on hepatic lipid accumulation and metabolism in tiger puffer fed normal or high-lipid diets. An 8-week feeding trial was conducted in an indoor flow-through seawater system. Two diets with suitable (8.5%, diet C) or high lipid level (12.5%, diet HL) were prepared. BA, a porcine bile extract mainly comprised of hyodeoxycholic acid was supplemented into the two diets at the level of 0.02% to formulate diet CBA and diet HLBA, respectively. A fifth diet was prepared by supplementing an excess level of porcine bile extract (0.10%) into diet C (diet CHBA). Each diet was randomly fed to triplicate tanks. Dietary BA supplementation did not significantly affect fish growth performances. Dietary BA tended to decrease the whole-body lipid content, liver lipid content, hepatosomatic index, and viscerasomatic index in both fish fed with normal diets and fish fed with high-lipid diets. Similar results were observed for the contents of triacylglycerol, total cholesterol, and low-density lipoprotein-cholesterol in serum. The quantitative bile acid metabolomics analysis showed that taurocholic acid and taurochenodeoxycholic acid were dominantly abundant in the gallbladder. Dietary BA supplementation increased the concentration of taurohyodeoxycholic acid, glycohyodeoxycholic acid, and glycocholic acid, but affected some other BAs in various patterns. Dietary BA regulated hepatic transcription of lipid metabolism-related genes differentially in fish fed normal diets and fish fed high-lipid diets, decreasing the transcription of lipogenic genes in fish fed normal diets but increasing the transcription of genes related to lipid digestion and lipid/cholesterol transport in fish fed high-lipid diets. In conclusion, dietary BA supplementation tended to reduce the lipid accumulation in juvenile tiger puffer. However, at the transcription level the regulation of lipid metabolism by dietary BA seemed very different between fish fed normal diets and fish fed high-lipid diets. This study contributes to the general knowledge of bile physiology under different nutritional conditions in teleost and is beneficial to lipid management in tiger puffer farming.