| Large yellow croaker(Larimichthys crocea),as the first marine fish in mariculture in China,has less research on replacing fish meal with animal protein source.In this study,the juvenile large yellow croaker were selected,and chicken liver meal,fish chop meal,meat and bone meal were replaced with fish meal at the proportion of 0%,25%,50%,75%,and 100% to prepare five feed treatment groups with equal nitrogen and fat content.Each treatment was randomly allocated to four floating seawater cages(1 m × 1 m × 1.5 m),50 fish were placed in each cage for an 8-week aquaculture experiment.Exploring the optimal proportion and growth response mechanism of replacing fish meal with different animal protein sources in yellow croaker feed from aspects such as growth performance,digestive enzyme activity,antioxidant capacity,m TOR signaling pathway,and intestinal health.The specific results are as follows:1.Effects of chicken liver meal instead of fishmeal on growth,digestion and intestinal health of juvenile yellow croakerCompared with the CLM0,there was no significant difference in survival rate(SR)between groups(P > 0.05),weight gain rate(PWG),specific growth rate(SGR)and feed efficiency(FE)at replacement to 50%(P > 0.05),in terms of digestive enzyme activity,there was no significant effect when the replacement amounts of α-amylase(AMS),lipase(LPS)and trypsin reached 50%(P > 0.05),and in terms of antioxidant capacity,catalase(CAT)and total antioxidant enzyme(T-AOC)had no significant effect on the replacement amount of chicken liver powder to 50%(P >0.05).total superoxide dismutase(T-SOD)decreased with the increase of chicken liver meal replacement(P < 0.05),malondialdehyde(MDA)was significantly higher in CLM75 group and CLM100 group than CLM0,CLM25 and CLM50(P < 0.05).In terms of m TOR signaling pathway,the expression levels of m TOR protein in the CLM25 and CLM50 were significantly upregulated(P < 0.05),the expression level of m TOR protein in the CLM100 was significantly downregulated(P < 0.05),and the expression level of 4e-bp1 protein in the CLM75 and CLM100 was significantly downregulated(P < 0.05).In terms of intestinal morphological histology,there was no significant difference in intestinal villi height(VH)and intestinal villi width(VW)replacement to 50%(P > 0.05),there was no significant difference in intestinal wall thickness(MT)between groups(P > 0.05);In terms of intestinal flora,the CLM75 group and CLM100 group significantly increased the relative abundance of γ-Gammaproteobacteria and decreased the phase abundance of Clostridia,among which the CLM50 group significantly increased the relative abundance of beneficial bacteria Chitinophagales and Actinobacteriota.(P < 0.05).The above results indicate that replacing 50% of the fish meal in the diet of juvenile large yellow croaker with chicken liver meal is a reasonable alternative.Feeding chicken liver meal with different replacement levels may further affect growth by affecting the m TOR signaling pathway,and the intestinal flora is also Important factors in the response mechanism of chicken liver meal instead of fish meal for juvenile large yellow croaker.2.Effects of fish steak meal instead of fishmeal on growth,digestion and intestinal health of juvenile large yellow croakerCompared with FSM0,there was no significant difference in growth performance(P > 0.05)in SR between the groups.There was no significant difference in PWG and SGR when the substitution amount reached 25%(P > 0.05),and there was no significant difference in FE when the substitution amount reached 50%(P >0.05);In terms of digestive enzymes,there was no significant difference(P > 0.05)when the replacement amount of fish meal in AMS,LPS,and TPS reached 25%;In terms of antioxidant capacity,CAT showed no significant difference(P > 0.05)when the substitution amount reached 50%.T-AOC and T-SOD decreased with the increase of substitution amount(P < 0.05),while MDA in FSM75 and FSM100 was significantly higher than that in FSM0,FSM25,and FSM50 groups(P < 0.05);In terms of the m TOR signaling pathway,there was no significant difference in the expression level of m TOR protein when fish fillet meal substitution reached 50%(P >0.05),while the expression level of 4e-bp1 protein decreased with the increase of fish fillet meal substitution(P < 0.05);In terms of intestinal morphology and histology,there was no significant difference(P > 0.05)when the substitution levels of VH,VW,and MT reached 50%;In terms of intestinal flora,when the replacement amount is more than 50%,it significantly increases the relative abundance of harmful bacteria Photobacterium,and FSM25 significantly increases the relative abundance of beneficial bacteria Lachnospiraceae to promote intestinal health.The above results indicate that replacing 25% of fish meal in the feed of juvenile yellow croaker with fish meal is a reasonable alternative solution.Feeding fish meal with different levels of substitution may further affect growth through the m TOR signaling pathway,and gut microbiota is also an important factor in the response mechanism of replacing fish meal with fish meal in the feed of juvenile yellow croaker.3.Effects of meat and bone meal instead of fishmeal on growth,digestion and intestinal health of juvenile large yellow croaker3.Effects of meat and bone meal instead of fish meal on growth,digestion and intestinal health of juvenile large yellow croakerCompared with MBM0,there was no significant difference in growth performance(P > 0.05)in SR between the groups,and there was no significant difference in PWG,SGR,and FE when the substitution amount was 50%(P > 0.05);In terms of digestive enzymes,there was no significant difference when the replacement amount of meat and bone meal in AMS,LPS and TPS reached 25%(P>0.05);In terms of antioxidant capacity,CAT and T-AOC had no significant effect when the replacement amount of meat and bone meal reached 50%(P > 0.05).T-SOD decreased with the increase of replacement amount of meat and bone meal(P < 0.05).MDA was significantly higher in MBM75 and MBM100 than in MBM0,MBM25 and MBM50(P < 0.05);In terms of the m TOR signaling pathway,the expression levels of MBM25 and MBM50 m TOR proteins were significantly upregulated(P <0.05),while the expression level of 4e-bp1 protein was significantly downregulated(P< 0.05)when the MBM substitution amount was greater than 50%;In the influence of meat and bone meal on intestinal histomorphology,there was no significant difference when the VH replacement amount reached 25%(P > 0.05),there was no significant difference when the VW and MT replacement amount reached 50%(P > 0.05),and MBM75 and MBM100 were significantly lower than other groups(P < 0.05);In terms of intestinal flora,MBM75 and MBM100 increased the relative abundance of Vibrionaceae,MBM25 increased the relative abundance of Oscillospirales,and MBM50 increased the relative abundance of Spirillaceae.The above results indicate that replacing 50% of the fish meal in the diet of juvenile large yellow croaker with meat and bone meal is a reasonable alternative.Feeding meat and bone meal with different replacement levels may further affect growth through the m TOR signal pathway,and intestinal flora is also one of the important factors in the response mechanism of replacing fish meal with meat and bone meal in the diet of juvenile large yellow croaker.The above results show that replacing 50% of the fishmeal in the feed of large yellow croaker with meat and bone meal is a reasonable alternative,feeding different levels of meat and bone meal may further affect the growth through the m TOR signaling pathway,and the intestinal flora is also one of the important factors in the response mechanism of replacing fishmeal with meat and bone meal in juvenile feed of large yellow croaker.To sum up,chicken liver meal,fish chop meal and meat and bone meal can partially replace fish meal in the feed of juvenile large yellow croaker,and will not affect its growth and digestion,antioxidant enzymes,and intestinal health.The optimal replacement amount is 50%,25%,and 50%. |
