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The aim of the present study was to investigate the effects of dietary Zn level on growth performance, Zn bioaccumulation, antioxidant capacity and innate immunity in juvenile mud crabs (Scylla paramamosain). Six semi-purified diets were formulated to contain dietary Zn levels of 44·5, 56·9, 68·5, 97·3, 155·6 or 254·7 mg/kg. Dietary Zn level significantly influenced percentage weight gain (PWG), with the highest observed in crabs fed the diet containing 97·3 mg/kg Zn. Tissue Zn concentrations significantly increased as dietary Zn levels increased from 44·5 to 254·7 mg/kg. Retention of Zn in hepatopancreas increased with dietary Zn levels up to 68·5 mg/kg and then significantly decreased. Moreover, inadequate dietary Zn (44·5 and 56·9 mg/kg) reduced antioxidation markers including total superoxide dismutase (SOD) and Cu/Zn SOD activities and total antioxidant level. Crabs fed the diet with 44·5 mg/kg Zn also showed significantly lower expression of genes involved in antioxidant status, such as Cu/Zn SOD, glutathione peroxidase, catalase and thioredoxin than those fed diets containing 68·5 and 97·3 mg/kg Zn. The highest activities of phenoloxidase and alkaline phosphatase were recorded in crabs fed the diets containing 68·5 and 97·3 mg/kg Zn. Expression levels of prophenoloxidase and toll-like receptor 2 were higher in crabs fed the 97·3 mg/kg Zn diet compared with crabs fed the other diets. Based on PWG alone, the optimal dietary Zn level was estimated to be 82·9 mg/kg, with 68·5 to 97·3 mg/kg recommended for maintaining optimal Zn bioaccumulation, oxidation resistance and innate immune response of juvenile mud crabs.

An 8-week feeding trial was conducted to evaluate the effects of dietary xylanase supplementation on growth performance, digestive enzyme activity, intestinal morphology parameter, intestinal microbiome diversity, and carbohydrate metabolism for juvenile large yellow croaker (Larimichthys crocea). Four levels of xylanase were added to basal diets (0, 600, 1200, and 1800 U kg -1 ). The results indicated that fish fed the 1200 U kg -1 xylanase diet had higher weight gain than those fed the 0 and 600 U kg -1 xylanase diet. The highest intestinal folds and microvillous height were observed at fish fed the 1200 U kg -1 xylanase diet. High-throughput sequencing revealed that the majority of reads derived from the large yellow croaker digesta belonged to members of Proteobacteria followed by Chloroflex, Bacteroidetes, Spirochaetae, and Firmicute. Supplementation of xylanase in diets increased the relative abundance of Bacteroides and Gemmatimonadete. The higher hepatic glucokinase (GK) and glucose-6-phosphate dehydrogenase (G6PD) activities were observed in fish fed the xylanase supplementation diet. Accordingly, dietary xylanase supplementation upgraded the relative expressions of gk and g6pd genes in liver. In conclusion, optimum dietary xylanase supplementation (600-1200 U kg -1 ) could improve the growth performance, optimize the intestinal morphology structure and microbiota constitution, and enhance the ability of carbohydrate utilization of juvenile large yellow croaker.

An 8‐week feeding trial was conducted to investigate the effects of DL‐methionyl‐DL‐methionine (Met‐Met) supplementation in different fishmeal levels on growth performance, antioxidant and immune response of juvenile Pacific white shrimp, Litopenaeus vannamei. Eight isonitrogenous and isolipidic experimental diets were formulated to meet the nutrient requirements of Pacific white shrimp. The supplemental amount of fishmeal in diets without essential amino acid supplementation are 200 g/kg (F20), 100 g/kg (F10), 50 g/kg (F5) and 0 g/kg (F0), and with essential amino acid supplementation are 200 g/kg (M20), 100 g/kg (M10) 50 g/kg (M5) and 0 g/kg (M0) respectively. The results indicated that shrimp fed the F5 and F0 diets had significantly lower final body weight (FBW), per cent weight gain (PWG), specific growth rate (SGR) and higher feed conversion ratio (FCR) compared with those fed the F20 diet (p <.05). Glucose (GLU), triacylglycerol (TG) and cholesterol (CHO) concentration in haemolymph significantly decreased with fishmeal supplementation decreasing from 200 g/kg to 0 g/kg (p <.05). Met‐Met supplementation in low fishmeal diets significantly reduced the content of malondialdehyde (MDA), increased the activities of acid phosphatase (ACP) and lysozyme (LZM) in hepatopancreas, as well as increasing the activity of total antioxidant capacity (T‐AOC) in haemolymph (p <.05). Meanwhile, shrimp fed M5 and M0 diets had significant upregulation of gene expression of acp, lzm (immune‐related), RagC and s6k (TOR signalling pathway‑related) in hepatopancreas (p <.05). In conclusion, the present study demonstrated that dietary Met‐Met supplementation could improve the growth performance and the abilities of antioxidant and non‐specific immunity of Pacific white shrimp by reducing MDA concentration, increasing T‐AOC, ACP and LZM activities, and upregulating gene expression level of immune (acp and lzm) and TOR signalling pathway (RagC, and s6k). Moreover, Pacific white shrimp fed low fishmeal diets had the positive response of well‐balanced amino acid, and the results will provide further insight into the possibility of reducing fishmeal content in the commercial feed of shrimp. [ABSTRACT FROM AUTHOR]

Squid visceral paste is a popular attractant and feeding stimulator supplement in shrimp feeds in China, but it often faces problems with fluctuating availability, cost, composition, and quality. An 8‐week experiment was performed to test a proprietary palatability enhancer as an alternative to squid paste in white shrimp feed. Seven diets were tested: a control diet with no supplementations; S1 and S3 diets supplemented with squid paste at 1 or 3%, respectively; S1+PE0.1 and S1+PE0.15 supplemented with both 1% squid paste and the palatability enhancer at either 0.1 or 0.15%, respectively; and finally PE0.1 and PE0.15 supplemented only with the palatability enhancer at 0.1 or 0.15%, respectively. The results showed a trend for increased feed intake and weight gain when squid paste was added to the diet compared to the control, but this was worsened by raising the inclusion level from 1 to 3%. The inclusion of the PE, in combination with squid paste or alone at 0.15%, led to a significantly higher growth, and a feeding stimulation effect was also indicated, with PE0.1 and PE0.15 having a higher feed intake than the control. A further beneficial effect was a significant increase in protease activity in the hepatopancreas in the S1+PE0.15, PE0.1, and PE0.15 treatments compared to the control. In addition, a significant increase in the height of the intestinal mucosal folds was observed in PE0.15, followed by PE0.1. The results demonstrated the potential to replace or reduce squid visceral paste in shrimp diets by supplementing with a PE with functional effects beyond feeding stimulation. [ABSTRACT FROM AUTHOR]