Effects Of Feeding Frequency On The Growth,Immune And Digestion Performance Of Largemouth Bass Reared In In-Pond Raceway Culture Systems

To achieve a green and healthy model and a real-time online monitoring water quality network system as well as waste treatment device and water and oxygen equipment and green purification of plants and animals,the in-pond raceway culture systems(IPRS)uses intensive forms and space resources which enable small-scale centralized fish farming,large area water purification.Under this culture system,farming micropterus salmoides has significant advantages compare with other environment.Feeding frequency directly affects the water environment and feed utilization,which further affects the healthy growth of fish.It is important to investigate on the feeding frequency of fish farmed in IPRS.Micropterus salmoides(body weight: 5.0 g ± 0.4 g)were randomly assigning to one of three feeding frequencies(2,3 and 4 times/d)and feeding for 120 d.Based on the knowledge of molecular biology and physiology to analyze the growth,growth genes,immune antioxidant capacity,digestive and absorptive capacity,and fat metabolism capacity;conclusion can be drawn that the appropriate feeding frequency can provide scientific reference for feeding strategy of industrial pond recycling aquaculture.1.Analysis of the growth,nutritional components and expression of GH and IGF-I genes in Micropterus salmoidesThe experimental data were used to analyze the effects of feeding frequency on the growth,body composition and expression of GH and IGF-I genes in large-mouth bass cultured in IPRS for 120 d.The results shown that the survival rate is as high as 90.07%-92.01%.No significant differences were observed in final body weight,weight gain and specific growth rate of fish fed different feeding frequencies on days 30 and 60(P>0.05).Fish fed 2 times/d showed higher growth than those fed 4 times/d on day 90,but had higher growth than those fed 3 times/d and 4 times/d on day 120.No significant differences were found in coefficient variation.The ash content of Micropterus salmoides in the fed 2 times/d was significantly higher than that in the fed 3 times/d and fed 4 times/d groups,while the crude lipid content in fed 2 times/d group was significantly higher than that in the other group(P<0.05)however,it had no significant statistical significance on the moisture and crude protein content between three groups(P>0.05).Fish fed 2 times/d exhibited higher IGF-1 m RNA expression on days 30 d,60 d and 120 d(P<0.05),while no significant difference was found on day 90.No significant difference was found in GH m RNA expression on days 30 d and 60 d,while fish fed 4 times/d exhibited lower GH m RNA expression than those fed 2 times/d on days 90 d and 120 d(P<0.05).2.Analysis of serum immunity,liver tissue health and antioxidant enzyme activity of Micropterus salmoidesEffects of feeding frequency on serum biochemical indexes,liver tissue health and liver antioxidant enzyme activities of Micropterus salmoides.No significant differences were found in serum alanine aminotransferase(ALT),Aspartate transaminase(AST),alkaline phosphatase(ALP)activities,lysozyme,cortisol and triglyceride(TG)content,hepatic total antioxidant capacity(T-AOC),glutathione peroxidase(GSH-PX)activities and malondialdehyde(MDA)content among fish fed at different feeding frequency(P>0.05).Serum total protein(TP),glucose(Glu)content and catalase(CAT)activity decreased,while total cholesterol(TC)content increased with increasing feeding frequency.Fish fed 2 times/d had higher hepatic total superoxide dismutase(T-SOD)than those fed 4 times/d on days 60,90 and 120(P<0.05).From the liver histological observation,the more severe the liver fat accumulation leads to the more serious liver damage,with increasing feeding frequency.Fish fed 4 times/d had occurrence rates of the hepatocyte vacuolization and nuclei shifting to the cellular periphery were much higher in fish fed other frequency.3.Analysis of the intestinal tissue health and digestive capacity of Micropterus salmoidesIn order to study the health of feeding frequency on Micropterus salmoides intestinal tissue,it was found that the fish fed 4 times/d showed the intestinal tissue appeared muscular layer thinner and villi integrity drop.Fish fed 4 times/d had higher growth than those fed at 3 times/d and 4 times/d on day 120.Fish fed 2 times/d showed thicker muscle layer than those fed 4 times/d.The feeding frequency on the digestive capacity of largemouth bass showed that the intestinal amylase activity of fish fed 2 times/d group was higher than fed 4 times/d,and the same lipase activity also showed similar results(P<0.05).4.Analysis of expression of HL and LPL genes in Micropterus salmoidesIn order to analyze the effect of feeding frequency on the HL and LPL m RNA expression of Micropterus salmoides in pond raceway culture systems,the HL and LPL m RNA expression of Micropterus salmoides were tested experimentally from April to July and found that the feeding frequency,It has significant effects on on HL and LPL m RNA expression in Micropterus salmoides.Fish fed 2 times/d exhibited higher LPL m RNA expression on days 60 d and 90d(P<0.05),while no significant difference was found on day 120.Fish fed at 2 times/d exhibited higher HL m RNA expression than those fed 3 times/d and4 times/d(P<0.05).According to comprehensive analysis,under the condition of full-fed feeding,the suitable feeding frequency of largemouth bass in circulating water culture in ponds is fed 2 times/d.