The characteristics of glucose homoeostasis in grass carp and Chinese longsnout catfish after oral starch administration: a comparative study between herbivorous and carnivorous species of fish.

An oral starch administration trial was used to evaluate glucose homoeostasis in grass carp (Ctenopharyngodon idella) and Chinese longsnout catfish (Leiocassis longirostris Günther). Fish were administered with 3 g of a water and starch mixture (with 3:2 ratio) per 100 g body weight after fasting for 48 h. Fish were sampled at 0, 1, 3, 6, 12, 24 and 48 h after oral starch administration. In grass carp, plasma levels of glucose peaked at 3 h but returned to baseline at 6 h. However, in Chinese longsnout catfish, plasma glucose levels peaked at 6 h and returned to baseline at 48 h. The activity of intestinal amylase was increased in grass carp at 1 and 3 h, but no significant change in Chinese longsnout catfish was observed. The activity of hepatic glucose-6-phosphatase fell significantly in grass carp but change was not evident in Chinese longsnout catfish. The expression levels and enzymic activity of hepatic pyruvate kinase increased in grass carp, but no significant changes were observed in the Chinese longsnout catfish. Glycogen synthase (gys) and glycogen phosphorylase (gp) were induced in grass carp. However, there was no significant change in gys and a clear down-regulation of gp in Chinese longsnout catfish. In brief, compared with Chinese longsnout catfish, grass carp exhibited a rapid increase and faster clearance rate of plasma glucose. This effect was closely related to significantly enhanced levels of digestion, glycolysis, glycogen metabolism and glucose-induced lipogenesis in grass carp, as well as the inhibition of gluconeogenesis.

Effects of dietary yeast hydrolysate on the growth, antioxidant response, immune response and disease resistance of largemouth bass (Micropterus salmoides).

A 56-day growth trial was conducted to investigate the effects of dietary yeast hydrolysate on the growth performance, antioxidation, immune response and resistance against Aeromonas hydrophila in largemouth bass. Four experimental diets were prepared with yeast hydrolysate levels of 0% (Y0), 1.5% (Y1.5), 3.0% (Y3.0) and 4.5% (Y4.5). Each diet was randomly assigned to triplicate 150-L tanks and each tank was stocked with 30 largemouth bass (initial body weight, IBW = 7.71 ±â€¯0.02 g). A challenge test was carried out after the feeding trial by injecting A. hydrophila intraperitoneally for 4-day observation. The results showed that the FBW and WGR in Y1.5 group were significantly higher than those in Y0 group (P < 0.05) and the feed conversion ratio (FCR) got the lowest value in Y1.5 group. And the hydrolysate supplement significantly increased the 4-day cumulative survival rate after the bacterial challenge (P < 0.05). The plasma malondialdehyde was lower in the yeast hydrolysate supplement groups in both pre- and post-challenge test (P < 0.05), while the plasma C3 increased (P < 0.05). In post-challenge test, the plasma superoxide dismutase (SOD) and catalase (CAT) activities increased in the Y1.5 and Y3.0 groups respectively (P < 0.05), and plasma lysozyme in Y1.5 group and the plasma IgM in Y3.0 group were higher than those in others respectively (P < 0.05). For the q-PCR results, in post-challenge test, the hepatic hep2 expression level in Y1.5 and Y4.5 groups were both significantly higher than those in others (P < 0.05), as well as il-8 in Y3.0 group. The spleen hif-1alpha and tgf-beta1 expression levels in Y4.5 group were all significantly lower than those in others (P < 0.05), while the gilt was significantly higher (P < 0.05) in the post-challenge test. And the expression levels of spleen tnf-alpah1 in Y1.5 and Y3.0 groups and il-8 in Y3.0 group were all significantly higher than those in other groups (P < 0.05) in the post-challenge test. The head kidney gilt expression level was significantly higher in the yeast hydrolysate supplement groups compared with the Y0 group (P < 0.05), and the head kidney il-8 expression level in Y1.5 group was significant higher than those in other groups in post-challenge test (P < 0.05). The present results indicated dietary yeast hydrolysate improved the antioxidant ability and enhanced the immune response of largemouth bass without negative effect on growth. And 1.5% or 3.0% of dietary yeast hydrolysate was recommended for largemouth bass based on the present results.

Effects of dietary Tenebrio molitor meal on the growth performance, immune response and disease resistance of yellow catfish (Pelteobagrus fulvidraco).

This study evaluated the influence of diets containing mealworm (Tenebrio molitor) meal in partial substitution of fishmeal on growth performance and immune responses of juvenile yellow catfish (Pelteobagrus fulvidraco). Four diets were formulated to contain 0 (the control diet), 9, 18 and 27 g mealworm meal per 100 g diet with 0%, 25%, 50% and 75% of fishmeal replacement, respectively. Yellow catfish were randomly divided into 4 groups with 3 replicates in each group. The fish in each group were fed with one of the four experimental diets for 5 weeks. Growth performance, plasma parameters (SOD, MDA, IgM, C3, lysozyme) and immune related genes (MHC II, IL-1, CypA, IgM, HE) of yellow catfish were determined at the end of the feeding trial, as well as 24 h post bacterial (Edwardsiella ictaluri) challenge. The present results showed that dietary inclusion of mealworm meal (MW) had no negative effects on the growth performance of the juvenile yellow catfish, compared to the control group. At the end of the feeding trial, plasma MDA contents of MW supplemented groups were significant lower than the control group. Plasma SOD activities increased significantly with the increasing dietary MW contents at the end of feeding trial (pre-challenge) and 24 h post challenge with E. ictaluri. Significant increase of plasma lysozyme activity was found in MW supplemented groups compared to the control group 24 h post bacterial challenge. Plasma IgM levels increased significantly with the increasing dietary MW contents at the end of feeding trial. Compared with the control group, the immune related genes of MHC II, IL-1, IgM and HE of the fish in the MW supplemented groups significantly upregulated pre-challenge or 24 h post bacterial challenge. Finally, it was observed that the survival rate of the 27% MW group was significant higher (P < 0.05) than the control group but was not significantly differed from the 18% MW group. The present results indicated that dietary inclusion level of at least 18% MW could improve the immune response and the bacterial resistance of yellow catfish without any negative growth effects.