Evaluation of Dietary Essential Amino Acid Supplementation on Growth, Digestive Capacity, Antioxidant, and Intestine Health of the Juvenile Redclaw Crayfish, Cherax quadricarinatus.

The present study was an 8-week feeding trial investigating the effects of lysine and threonine supplementation in vegetable-based diets on growth, antioxidative capacity, and gut microbiota of juvenile redclaw crayfish, Cherax quadricarinatus (initial weight 11.52 ± 0.23 g). The lysine and threonine were supplemented to formulate five isonitrogenous (37%) and isolipidic (9%) diets containing 0% (control), 0.2% lysine (L0.2), 0.2% threonine (T0.2), 0.4% lysine (L0.4), and 0.4% threonine (T0.4), respectively. Compared to the control, weight gain rate (WGR) and specific growth rate (SGR) of C. quadricarinatus significantly increased with increasing dietary lysine and threonine supplementation from 0.2% to 0.4% (P < 0.05). Hepatopancreas trypsin activity significantly increased with increasing levels of lysine and threonine in diets (P < 0.05). However, the pepsin, lipase, and amylase activities were not affected by dietary levels of lysine and threonine (P > 0.05). Compared with the control, crayfish in T0.4 and L0.4 showed significantly higher glutathione peroxidase (GPx) activity (P < 0.05), lower alanine aminotransferase (ALT) activity, and lower malondialdehyde (MDA) content (P < 0.05). Supplementation with 0.4% lysine significantly changed the composition of the gut microbiota (P < 0.05), which showed a significantly increased relative abundance of Proteobacteria and decreased Firmicutes, Actinomycetes, and Pontomyces (P < 0.05). The PICRUSt analysis demonstrated that the abundance of the metabolism and cellular processes pathways in the L0.4 group were markedly decreased compared with the control (P < 0.05). Meanwhile, a tighter interaction of the microbiota community in crayfish was observed in the T0.4 experimental group. In conclusion, these results suggested that dietary supplementation with 0.4% threonine could significantly promote growth and improve microbial health in juvenile C. quadricarinatus.

Effects of dietary plant protein sources intake on growth, digestive enzyme activity, edible tissue nutritional status and intestinal health of the omnivorous Redclaw crayfish, Cherax quadricarinatus.

For the omnivorous Cherax quadricarinatus crayfish, plant raw materials can be good alternatives to dietary fish meal (FM). A 56-d feeding trial was conducted in C. quadricarinatus (11·70 (se 0·13) g). Diet with 100 % FM as the protein source was the control. Seven experimental diets were formulated by replacing 75 or 100 % of FM with soyabean meal (SM75, SM100) or cottonseed meal (CM75 and CM100), and a mixture of SM and CM (protein content is 1:1) replacing 50, 75 or 100 % of FM (SC50, SC75 and SC100). Crayfish fed the CM100 and SC100 showed significantly lower weight gain (WG), specific growth rate, trypsin and pepsin activities compared with the control diet. Crayfish in CM100 group showed significantly higher GPx, alanine aminotransferase, aspartate aminotransferase activities and malondialdehyde content than the control. SM100 and CM100 diets can cause slight separation of the peritrophic membrane from the intestinal folds. The pepsin activity of crayfish in SC50 was significantly higher than those in other experimental diets. The highest WG and muscle arginine content were also found in crayfish fed SC50. The relative abundance of Proteobacteria, Unclassified Enterobacteriaceae and Candidatus Bacilloplasma was significantly higher, but Actinobacteriota was significantly lower in SM100, CM100 and SC100 than in control. Microbiota functional prediction indicated that the relative abundance of 'cell motility' pathway in crayfish fed CM100 was significantly decreased compared with the control. In conclusion, only half of the FM can be effectively substituted with a mixture of SM and CM (protein content is 1:1) for C. quadricarinatus.

Toxic effect of chronic waterborne copper exposure on growth, immunity, anti-oxidative capacity and gut microbiota of Pacific white shrimp Litopenaeus vannamei.

Copper can be accumulated in water through excessive sewage discharge or residual algaecide to generate toxic effect to aquatic animals. In this study, the juvenile of Pacific white shrimp, Litopenaeus vannamei was exposed to 0 (control), 0.05, 0.1, 0.2, 0.5 or 1 mg Cu2+ L-1 for 30 days. Growth, immune function, anti-oxidative status and gut microbiota were evaluated. Weight gain and specific growth rate of L. vannamei were significantly decreased with the increase of ambient Cu2+. Enlarged lumen and ruptured cells were found in the hepatopancreas of shrimp in the 0.5 or 1 mg Cu2+ L-1 treatment. Total hemocyte counts of shrimp in 0.5 or 1 mg Cu2+ L-1 were significantly lower than in the control. The hemocyanin concentration was also significantly increased in 0.2 or 0.5 mg Cu2+ L-1. Lysozyme contents were reduced in shrimp when Cu2+ exceeded 0.2 mg L-1. Meanwhile, activities of superoxide dismutase and glutathione peroxidase were increased in the hepatopancreas and the activity of Na+-K+ ATPase was decreased in the gills with increasing Cu2+. The mRNA expressions of immune deficiency, toll-like receptor and caspase-3 were all significantly higher in the hepatopancreas in 0.05 mg Cu2+ L-1 than in the control. For the diversity of intestinal microbes, Bacteroidetes significantly decreased in 1 mg Cu2+ L-1 at the phylum level. KEGG pathway analysis demonstrates that 1 mg L-1 Cu2+ can significantly alter metabolism, cellular processes and environmental information processing. This study indicates that the concentration of 1 mg L-1 Cu can negatively impact growth, hemolymph immunity, anti-oxidative capacity and gut microbiota composition of L. vannamei.

Growth and health status of Pacific white shrimp, Litopenaeus vannamei, exposed to chronic water born cobalt.

Cobalt (Co) is an important component of vitamin B12, but is toxic to aquatic animals at a high level. In this study, the Pacific white shrimp, Litopenaeus vannamei were exposed to three Co concentrations (0, 100, and 1000 µg/L) for 4 weeks. The survival and condition factor in shrimp exposed to the Co treatments were not different from the control, but the shrimp exposed to 100 µg Co/L gained more weight than in other two groups, and the shrimp exposed to 1000 µg Co/L gained less weight than in other groups. The SOD and GSH-PX activities were higher in shrimp exposed to 100 µg Co/L, but lower in the shrimp exposed to 100 µg Co/L compared with the control, respectively. The MDA contents in the hepatopancreas decreased in the 100 µg Co/L, but increased in the 1000 µg Co/L. The serum lysozyme decreased with ambient cobalt, was lower in the shrimp exposed to 1000 µg Co/L than in other two groups. The expression of C-type lectin 3 was down-regulated by Co concentrations. The Toll and immune deficiency in shrimp exposed to 100 µg Co/L was higher than in other two groups. The mucin-1 was lower in the 1000 µg Co/L group than in other two groups, but mucin-2 and mucin-5AC were higher in the 1000 µg Co/L group than in the control. With increasing Co concentration, Shannon and Simpson indexes of the intestinal microbial communities were decreased. The abundance of pathogenic bacteria (Ruegeria and Vibrio) increased in both Co groups. This study indicates that chronic exposure to waterborne cobalt could affect growth, cause oxidative stress, stimulate the immune response, damage intestinal histology, and reshape intestinal microbiota community L. vannamei.