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.

Two 70-day feeding trials were conducted to reevaluate the necessity of cholesterol supplementation in diets of two important marine fish species, turbot and tiger puffer. Graded levels (0, 0.5, 1.0, 2.0, and 4.0 of dry matter) of cholesterol were added into the basal diet (with 30 fishmeal but no fish oil) to make five experimental diets, which were designated as control, CHO-0.5, CHO-1.0, CHO-2.0, and CHO-4.0, respectively. The dietary cholesterol concentration was measured to be 0.11, 0.65, 1.10, 2.32, and 4.59, respectively. Each group had triplicate tanks, and each tank was stocked with 30 fish. The results showed that compared to the control, dietary cholesterol supplementation had no significant effect on the growth of both turbot and tiger puffer. Nevertheless, excess dietary cholesterol (CHO-2.0 and CHO-4.0) led to significant lower weight gain of tiger puffer compared to CHO-1.0. The feed intake decreased with increasing levels of dietary cholesterol. In general, the cholesterol supplementation decreased the crude lipid content in the liver, whereas 0.5 dietary cholesterol supplementation tended to increase the crude lipid content in the muscle of both species. Dietary cholesterol supplementation significantly regulated the lipid-related biochemical parameters in serum, liver, and muscle, and compared to turbot, tiger puffer lipid compositions had a higher buffering capacity in response to changes in dietary cholesterol level. Dietary cholesterol supplementation increased the 20:4n-6 content in the liver. Dietary cholesterol supplementation significantly downregulated the gene expression of HMG-COAr, upregulated the CYP7A1 expression, and downregulated the expression of lipid absorption and biosynthesis genes, but had no significant effect on gene expression of CPT1 and lipid transport-related genes (ApoA1, ApoA4, ApoB100, and ApoEα) in the liver. In conclusion, under the present experimental condition, dietary cholesterol supplementation had no significant effect on the growth of turbot and tiger puffer. In both species, dietary cholesterol supplementation significantly regulated the lipid accumulation and metabolism.

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.

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

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