Yong-Jian Liu

High-fat diet (HFD) usually induces oxidative stress and astaxanthin is regarded as an excellent anti-oxidant. An 8-week feeding trial was conducted to investigate the effects of dietary astaxanthin supplementation on growth performance, lipid metabolism, antioxidant ability, and immune response of juvenile largemouth bass (Micropterus salmoides) fed HFD. Four diets were formulated: the control diet (10.87% lipid, C), high-fat diet (18.08% lipid, HF), and HF diet supplemented with 75 and 150 mg kg⁻¹ astaxanthin (HFA1 and HFA2, respectively). Dietary supplementation of astaxanthin improved the growth of fish fed HFD, also decreased hepatosomatic index and intraperitoneal fat ratio of fish fed HFD, while having no effect on body fat. Malondialdehyde content and superoxide dismutase activity were increased in fish fed HFD, astaxanthin supplementation in HFD decreased the oxidative stress of fish. The supplementation of astaxanthin in HFD also reduced the mRNA levels of Caspase 3, Caspase 9, BAD, and IL15. These results suggested that dietary astaxanthin supplementation in HFD improved the growth performance, antioxidant ability and immune response of largemouth bass.

The dipeptide dl-methionyl-dl-methionine (Met-Met) has extremely low water solubility and better absorption than other methionine sources (such as dl-methionine and l-methionine) available in the market. Therefore, six diets (D1, D2, D3, D4, D5 and D6) containing 0, 0·07, 0·15, 0·21, 0·28 and 0·38 % Met-Met were formulated to investigate the effects of Met-Met in juvenile Nile tilapia, Oreochromis niloticus (17 g initial body weight). The results indicated that percentage weight gain and specific growth rate of fish fed with D2 and D3 diets were higher than those fed with D1, D4–D6 diets. The levels of total essential amino acid in whole body of fish fed with D3 and D4 diets were significantly higher than those fed the D1 diet. Superoxide dismutase activity and malondialdehyde content have no significant difference in fish fed the diet with or without Met-Met supplementation. Majority of reads derived from the fish intestine belonged to members of Fusobacteria, followed by Bacteroidetes and Proteobacteria. Diversity of intestinal microbiota and total antioxidant capacity in fish fed with D3 diet was significantly higher than that of other groups. Based on the growth results, the authors conclude that the optimal level of Met is 0·61 % Met with the addition of 0·15 % Met-Met for grower-phase O. niloticus.

The study was conducted to compare and evaluate effects of four different macro-algaes on growth, immune response, and intestinal microbiota of Litopenaeus vannamei. In the rearing trial 1, shrimp were fed five diets containing four sources of macro-algaes for 8 weeks, named D1 (without macro-algae), D2 (Porphyra haitanensis), D3 (Undaria pinnatifida), D4 (Saccharina japonica), and D5 (Gracilaria lemaneiformis), respectively. Growth performance of shrimp in D5 diet was significantly higher than that of shrimp fed the control and D4 diet (P < 0.05); however, there is no significant difference among D2, D3, and D5 diets (P > 0.05). Apparent digestibility coefficients of dry matter from the D2, D3, and D5 diets were significantly higher than that from the control and D4 diets (P < 0.05). Supplementary macro-algaes enhanced hepatopancreas immunity through positively increasing total antioxidant status (TAS) and prophenoloxidase activity (ProPO), as well as up-regulating the hepatopancreas RNA expression of ProPO and IκBα and down-regulating the expression of transforming growth factor β. Furthermore, dietary macro-algaes modified intestinal microbiota of L. vannamei, boosting the relative abundance of beneficial bacterial such as Bacteroidetes, Firmicutes, and Bacillaceae, and decreasing those detrimental bacterial such as Gammaproteobacteria and Vibrionaceae. In the white spot syndrome virus (WSSV) challenge trial, shrimps were injected for 6-day after the rearing trial. On the fourth day, shrimp death started to occur, and the mortality in D2, D3, and D5 diets was significantly lower than that in control and SJ diets during 4–6 challenged days (P < 0.05). Dietary macro-algaes ameliorated hepatopancreas damage in L. vannamei by increasing TAS and ProPO activities and decreasing SOD activity, inhibiting the lipid peroxidation (malondialdehyde), as well as regulating the immune-related genes expression. Taken together, dietary macro-algaes availably relieved enterohepatic oxidative damage by improving antioxidant ability and immunity and regulated intestinal microbiota in L. vannamei. These results indicated that G. lemaneiformis is the most suitable macro-algae and then followed by U. pinnatifida and P. haitanensis as the feed ingredient for L. vannamei.

An 8-week feeding trial was conducted to evaluate the effects of ascorbic acid (AsA), in the form of l-ascorbyl-2-polyphosphate (LAPP) on growth performance, body composition, antioxidative capacity and salinity stress tolerance of juvenile Pacific white shrimp, Litopenaeus vannamei. Five practical diets (46% crude protein and 7.6% lipid) supplemented with graded levels of AsA (14.64, 48.55, 84.98, 308.36 and 639.27 mg kg⁻¹ diet) were fed to five replicate groups of L. vannamei (mean initial wet weight 0.57 g). No significant differences were found on growth performance among all treatments. However, whole body lipid content significantly decreased with dietary AsA levels increasing. Activities of total antioxidant capacity, glutathione reductase and glutathione peroxidase were significantly affected by dietary AsA levels. Shrimp fed LAPP-free diet had higher malondialdehyde content than those fed the diets supplemented with LAPP. Dietary AsA levels higher than 308.36 mg kg⁻¹ diet increased the survival of shrimps after 1, 2 and 3 h of acute salinity change. Broken-line regression analysis on survival after 3 h of salinity stress and second-degree polynomial regression analysis on glutathione reductase data indicated that the optimal dietary AsA requirement of L. vannamei was estimated to be 306.39, 319.75 mg kg⁻¹ diet respectively.

An 8-week feeding trial was conducted to evaluate the effect of N-acetyl cysteine (NAC) and glycine supplementation on growth performance, glutathione (GSH) synthesis, and antioxidative ability of grass carp, Ctenopharyngodon idella. Four practical diets were formulated: control, control + 0.2% NAC, control + 0.5% glycine, and control + 0.2% NAC + 0.5% glycine. Each diet was randomly assigned to quadruplicate groups of 30 fish (approximately 8.8 g). Weight gain and specific growth rate were significantly increased with the supplementation of NAC. Supplementation of NAC plus glycine significantly increased the feed efficiency. Glutathione peroxidase (GPx) and γ-glutamine cysteine synthase (γ-GCS) in plasma were significantly increased with the supplementation of NAC plus glycine. GSH in plasma increased and malondialdehyde (MDA) decreased in fish fed diets supplemented with NAC. Respiratory burst, superoxide dismutase (SOD), and catalase (CAT) activity were not affected by NAC or glycine. These results clearly indicated that NAC improved the growth performance and restored GSH of grass carp, supplemented NAC together with glycine enhanced GSH synthesis, and improved the antioxidative ability of grass carp.