Effects Of All-plant-based Diet On Growth Performance,Digestive Function, Anti-stress Properties And Two HSP70s MRNA Expressions Of Blunt Snout Bream

Blunt snout bream(Megalobrama amblycephala) has been regarded as a principal species in the Chinese fresh-water culture systems. However, the diets used widely in pisciculture differ from available experimental results, especially in the fish meal application. In this sense, six all-plant-based pellet diets and extruded diets differing in protein levels (22%,24%,26%,28%,30%and32%) as well as fish meal diet were formulated. The experiments were conducted for57d in order to investigate the dietary requirement of protein and suitable feed form by examining the growth performance and whole-body composition of blunt snout bream. Furthermore, we sought to study the influence of all-plant-based diet on blunt snout bream fingerlings by examining growth performance, anti-stress properties, digestive function and two HSP70s mRNA expressions as compared to the fish meal diet. The research results are as follows:1. The dietary requirement of protein and suitable feed form of blunt snout bream fed with all-plant-based dietThe results indicated that the weight gain, specific growth rate and protein efficiency ratio of blunt snout bream in each group showed a significant trend of decrease after the first increase (P<0.05) with the increasing dietary protein level whether fed with all-plant-based pellet or extruded diet and achieve maximum when the protein level was30%while the feed conversion ratio was on the contrary and reach minimum when the protein level was30%. The condition factor of blunt snout bream fed with all-plant-based extruded diet with the protein level of30%was significant lower than that of the protein level of26%(P<0.05), and was no significant different from other groups (P<0.05). However, the condition factor of blunt snout bream in each group fed with all-plant-based pellet diet showed a trend of decrease after the first increase and reach maximum when the protein level was30%, which was significant different from that of other groups except the protein level of26%. The crude lipid and ash of blunt snout bream was not influenced by the protein level whether fed with all-plant-based pellet or extruded diet (P>0.05). The moisture and crude protein of blunt snout bream showed the same trend with the increasing protein level and reach maximum when the protein level was30%. Blunt snout bream showed the best growth performance when the protein level was30%, and the weight gain, specific growth rate and protein efficiency ratio of Blunt snout bream fed with all-plant-based extruded diet were higher than that of all-plant-based pellet extruded diet while the feed conversion ratio was lower.2. Effects of all-plant-based diet on growth performance and digestive function of blunt snout breamThe results showed that both weight gain, specific growth rate and protein efficiency ratio of all-plant-based diet group were significant higher than those of the control (P<0.05). In contrast, feed conversion ratio of all-plant-based diet group was significantly lower than that of the control (P<0.05). No significant difference was observed in the viserosomatic index and hepatosomatic index between all-plant-based diet and the control group (P>0.05) while the condition factor of all-plant-based diet was significantly lower than that of the control.Compared with the control group, the intestinal protease activity of all-plant-based diet group decreased significantly (P<0.05), but no significant difference was observed in the intestinal amylase activity between all-plant-based diet and the control group (P>0.05). Furthermore, there was no significant difference in the thickness of fore-gut and mid-gut wall as well as the intestinal villus density (P>0.05). However, compared to the control group, the hind-gut wall of blunt snout bream fed with all-plant-based diet was thinner and the intestinal villus density also showed a certain degree of decrease.3. Anti-stress properties and two HSP70s mRNA expressions of blunt snout bream fed with all-plant-based dietThe influence of all-plant-based diet on fingerling blunt snout breams (Megalobrama amblycephala) was tested by examining anti-stress properties and related gene expression. Compared to the control group, the lysozyme levels in serum and mucus, and glutamic-oxaloacetic transaminase activities in serum and liver decreased significantly (P <0.05). In contrast, the glutamic-pyruvic transaminase activities in serum and liver increased significantly (P<0.05). For blunt snout breams fed with all-plant-based diets, the superoxide dismutase activities in mucus, serum and liver as well as catalase activity in serum and liver were decreased significantly (P<0.05) comparing with that of the control group. But malondialdehyde contents were higher (P<0.05) in serum and liver than that of control group. The expression of HSC70mRNA increased significantly (P<0.05) in blunt snout breams fed with all-plant-based diet, whereas the HSP70mRNA expression decreased significantly (P<0.05) when compared with control group.