Docosahexaenoic acid (DHA), a long-chain polyunsaturated fatty acid, plays a critical role in animal growth, inflammatory regulation, lipid metabolism, and neurological functions. However, the optimal dietary requirement of DHA for tiger puffer remains unknown. This study systematically investigated the effects of different dietary DHA levels on the growth performance, body composition, hematological parameters and tissue physiology of tiger puffer (average initial body weight 17.78 ± 1.92 g). Six experimental diets with graded DHA concentrations (0.09%, 0.57%, 1.35%, 1.61%, 2.28%, and 3.08% dry matter) were formulated. The feeding experiment was carried out in a seawater flow-through system for eight weeks, with each diet assigned to three replicate tanks. Based on the regression analysis of weight gain and specific growth rate, the maximum values were observed at the dietary DHA level of 1.75% and 1.88%, respectively. Appropriate DHA levels also significantly improved the muscle protein synthesis and lipid metabolism, and strengthened the intestinal morphology. Furthermore, a threshold for efficient DHA deposition in muscle was identified, beyond which excess DHA (3.08%) may be β-oxidized and therefore largely wasted. In conclusion, the optimal dietary DHA level for juvenile tiger puffer should be within the range of 1.75–1.88%.

Microalgal protein demonstrates considerable potential for reducing dependence on fishmeal in aquafeeds. However, limited research has been conducted on the effects of Chlorella pyrenoidosa meal (CM) on carnivorous fish species. This study evaluated the impact of replacing 0% to 40% of fishmeal with CM within isonitrogenous and isolipidic diets (designated as CM0, CM5, CM10, CM20, and CM40) on juvenile tiger puffer (initial weight: 11.34 ± 0.01 g) over a 56-day feeding trial. Three replicate tanks were established for each experimental group, with 30 fish per tank. The experimental data were statistically analyzed using one-way analysis of variance (ANOVA) and regression analysis. The results showed that no significant differences were observed in final body weight (FBW: CM0, 55.45 ± 1.87 g; CM40, 45.6 ± 2.09 g) or specific growth rate (SGR: CM0, 2.83 ± 0.06%/d; CM40, 2.48 ± 0.08%/d) among the dietary groups; however, the growth linearly decreased with increasing CM levels. The CM40 group exhibited a significantly higher feed conversion ratio (FCR: CM0, 1.17 ± 0.02; CM40, 1.28 ± 0.03). Muscle texture parameters (hardness, adhesiveness, cohesiveness, springiness, gumminess, and chewiness) and proximate composition were not significantly affected by dietary treatments. In contrast, the CM40 diet significantly decreased the n-3/n-6 polyunsaturated fatty acid (PUFA) ratio in the muscle, while increasing the contents of 18:2n-6 and total n-6 PUFAs. These results indicate that substituting up to 5% of fishmeal with CM did not produce significant adverse effects on growth or body composition, although linear trends indicated a progressive decline in performance at higher inclusion levels. This investigation provides valuable insights into the application of sustainable protein alternatives in feeds for marine carnivorous fish.

This study was conducted to explore the impacts of L-carnitine (CAR) on growth performance, antioxidant capacity, hepatic lipid deposition and fatty acid β-oxidation in farmed fish fed a high-fat diet (HFD). A total of 150 juvenile tiger puffer (15.23 ± 0.01 g) were randomly assigned into six tanks (three tanks each group) and fed with a control diet (HFD, 16% lipid) and a HFD supplemented with 1.5% CAR for eight weeks, respectively. The results indicated that the growth performance and the most proximate compositions were not influenced by dietary CAR. However, compared to the control group, the hepatosomatic index and crude lipid content in the liver were significantly reduced in the CAR group, indicating that CAR performed a lipid-lowering effect in tiger puffer. Serum lipid profiles remained stable, implying that the cholesterol metabolism was not influenced by dietary CAR. Furthermore, dietary CAR activated fatty acid β-oxidation (FAO) in both the mitochondria and peroxisomes and drove lipolysis and fatty acid intracellular transport to supply sufficient substrates for FAO, manifested by the activation of related genes, proteins and enzyme activity. Additionally, CAR lowered hepatic MDA levels, indicating improved antioxidant capacity. In conclusion, CAR shows potential as a lipid-lowering feed additive for marine fish under high-fat dietary conditions.

Hypoxia is a common environmental stress in nature and aquaculture, but the adaptation mechanisms of flatfish to chronic hypoxia and its effects on flesh quality remain unclear. In this study, the turbot was cultured at control normoxia (CON, 6.5 ± 0.5 mg/L) or chronic hypoxia (CHO, 3.5 ± 0.5 mg/L) for 8 weeks; then, the growth, energy metabolism, meat quality, and the expression of related genes were measured. The CHO group significantly reduced the digestibility (p < 0.05), weight gain (p < 0.001), and body indexes (p < 0.01), but increased feed conversion ratio (p < 0.001) in turbot. Meanwhile, the CHO group decreased muscle texture, total amino acid, soluble protein (p < 0.001), glycogen contents, and myofiber numbers (p < 0.001), while increasing myofiber diameters and lactate content (p < 0.01). In addition, chronic hypoxia increased the hepatic angiogenesis by activating the hif1α/vegfa pathway (p < 0.05) and decreased the whole fish lipid content and liver n-3 polyunsaturated fatty acid levels (p < 0.05). In summary, chronic hypoxia reduced the growth, nutrient content, and flesh quality of turbot. This study provides important references for elucidating the adaptation mechanisms of flatfish to chronic hypoxia and for developing mitigation strategies.

The n-3 long-chain polyunsaturated fatty acids (n-3 LC-PUFAs) have a key role in maintaining fish growth and health. However, fish oil (FO), the main source of n-3 LC-PUFAs, is in relative shortage due to the rapid development of the aquaculture industry. In this study, we investigated the efficacy of replacing fish oil with mixtures of algal oil (AO) from Schizochytrium sp. and terrestrially sourced oils (animal oil poultry oil (PO) or vegetable oil rapeseed oil (RO)) in the diets of juvenile tiger puffer (average initial body weight 23.8 ± 1.51 g). An 8-week feeding trial was conducted using three experimental diets: a control diet containing 6% added FO (control FO-C) and two diets with 3% AO + 3% PO or RO (groups AO+PO and AO+RO, respectively), replacing FO. Each diet was fed to triplicate tanks with 25 fish in each tank. The weight gain, feed conversion ratio, body composition, and serum biochemical parameters were not significantly different among the three groups, except that the AO+PO group had a significantly lower muscle lipid content than the other two groups. The AO-added diets significantly increased the DHA content in whole fish, muscle, and liver samples but significantly reduced the EPA content. The oil mixture treatments significantly increased the contents of monounsaturated fatty acid (MUFA) but significantly decreased the contents of saturated fatty acids (SFAs) in the liver and whole fish samples. However, the MUFA and SFA contents in the muscle samples were not significantly different among the dietary groups. The diets with oil mixtures did not affect the hepatic histology but tended to result in the atrophy of intestinal villi. The treatment diets downregulated the hepatic gene expression of proinflammatory cytokines (il-1β and tnf-α) and the fibrosis marker gene, acta2. However, the AO+PO diet inhibited the intestinal gene expression of the tight junction protein, claudin 18. In the muscle, the treatment diets upregulated the expression of genes related to cell differentiation and apoptosis (myod, myog, myf6, myf5, bcl-2, and bax). In conclusion, Schizochytrium sp. oil in combination with terrestrial oils (poultry oil or rapeseed oil) can be an effective alternative to fish oil in the diets of tiger puffer, but the mixing strategy may be better modified in consideration of intestinal health.

Our previous studies found that lipid emulsifiers can promote the absorption and deposition of liposoluble pigments in shrimp. The present study aimed to further investigate the effects of liposoluble pigments lutein (LUT) and lycopene (LYC), and their combination with lysophospholipids (LPL), on the growth performance, body coloration, and lipid composition of Pacific white shrimp Penaeusvannamei. Five diets were formulated: a control diet (Control), Control + 0.02% lutein (LUT), Control + 0.02% lycopene (LYC), LUT + 0.1% LPL (LUT + LPL), and LYC + 0.1% LPL (LYC + LPL). The feeding trial lasted for 8 weeks. There were no significant differences in shrimp growth and body composition among all groups. Both LUT and LYC increased the redness (a*) and yellowness (b*) of cooked shrimp. LPL synergistically enhanced the pigmentation-improving effects of LUT but weakened those of LYC. Additionally, LYC decreased the redness and yellowness of raw shrimp. Both LUT and LYC reduced the contents of saturated fatty acids and EPA while increasing the DHA content; LPL further enhanced this modulatory effect. In conclusion, LPL acts synergistically with LUT to improve the body coloration and modify the fatty acid composition of Pacific white shrimp, but its effect with LYC is limited.