Effect Of Niacin On Dietary Requirement And Stress Response Ability Of Juvenile Blunt Snout Bream, Megalobrama Amblycephala

The effect of niacin on growth performance, plasma biochemical indices, intestinal digestive enzyme activities and liver oxidation resistance capacity of juvenile blunt snout bream in this experiment was studied by single factor concentration gradient method. And the effect of niacin on regulating capacity of stress(heat stress and transport stress) of juvenile blunt snout bream also was studied by two-factor variance analysis method. The result will offer reference data for the feed formula for this species.Experiment 1 dietary niacin requirement of juvenile blunt snout bream, Megalobrama amblycephalaThis study, optimal dietary niacin requirement of juvenile blunt snout bream, was researched by single factor concentration gradient method.960 juvenile blunt snout bream(average initial weight:3.62±0.02g)were divided into 6 groups randomly, each group has 4 replicates. Fish was fed the actual niacin of each diet group containing different levels (0.31,10.37,20.15,31.24,40.05 and 49.56mg kg-1) for 8 weeks. The optimal niacin requirement of juvenile blunt snout bream was determined by growth performance, feed efficiency, proximate composition, plasma biochemical indices and liver niacin. The results show that weigh gain (WG), specific growth rate(SGR)(P<0.05) and survival rate(P<0.01)of juvenile blunt snout bream are improved significantly which fed diet with niacin. Meanwhile, feed conversion rate (FCR) get an opposite trend(P<0.01). Crude protein of whole body increase significantly from 0 to 20mg kg-1 niacin diets(P<0.01), Crude lipid of whole body showed a slow ascendant trend from 0 to 30mg kg-1, then showed significantly increase at 40 mg kg-1 comparing with 0 and 10 mg kg-2 (P<0.05). Moisture and ash of whole-body and proximate composition of carcass were no significantly difference among fish fed diets with various levels of niacin(P>0.05). Total cholesterol(TCHO) and high-density lipoprotein cholesterol (HDL-C) were on the rise, and then they reached the peak when feeding the fish of niacin 40 mg kg-1. The addition of niacin to diets significantly reduced plasma nonestesterified fatty acid (NEFA) and low density lipoprotein cholesterol (LDL-C) content (P<0.01). The niacin content in liver first increased then plateaued and it has significantly difference with increasing dietary niacin levels. Regression analysis showed that blunt snout bream juvenile were estimated to need mass fraction of niacin 29.85-32.25 mg kg-1 to maintain their maximum growth and normal physiological function.Experiment 2 Effects of dietary niacin levels on intestinal digestive enzyme activities and liver oxidation resistance capacity of juvenile blunt snout bream, Megalobrama amblycephalaAdopted juvenile blunt snout bream as experiment target, added niacin as influence factor, determined intestinal digestive and liver oxidation resistance enzyme activities, aimed to ascertain the effects of dietary niacin levels on intestinal digestive enzyme activities and liver oxidation resistance capacity of juvenile blunt snout bream. Methods for experiment design and analysis were the same to experiment 1. The results show that the activity of amylase was increased significantly(P<0.05) with 30 mg niacin kg-1 or above, but the activity of protease was not (P>0.05). The activity of lipase was decreased significantly from 0 mg kg-1 to 30 mg kg-1 niacin diet((P<0.01).There was significant positive correlation between Glutathione (GSH) and 20 mg kg-1 niacin diet (P<0.01). After that,there show nonsignificant decrease from 20 mg kg-1 to 50 mg kg-1(P>0.05),but it also higher than control group Catalase(CAT) and Total superoxide dismutase (T-SOD) have indistinctive increasing trend (P>0.05). However, Malondialdehyde (MDA) was decreased significantly with 40 mg niacin kg-1(P<0.01). So the right amount of niacin could improve enzyme activities of intestinal digestive and liver oxidation resistanceExperiment 3 Effects of dietary niacin levels on juvenile blunt snout bream, Megalobrama amblycephala, before and after transport stress and heat stress.The objective of this study was to investigate the effect of transport stress and heat stress on cortisol(COR), alanine aminotransferase(ALT) and aspartate transaminase (AST) of blunt snout bream.360 fish (body weight:(16.21±1.36)g) were randomly divided into four groups,each group has 3 replicates. Fish was fed the actual niacin of each diet group containing different levels (10.73,31.31,59.77 and 88.64 mg kg-1) for 45 days, and then controlling transport stress and heat stress. The result of transport stress was compared between before and after stress. Heat stress time was 24 hours on (34±1)℃, COR, ALT and AST were determined at 0,3,6,12 and 24h after heat stress respectively. The results showed that index of control group was increased significantly after transport stress(P<0.05). With increasing levels of niacin, plasma COR, ALT and AST showed a decreased trend before and after stress. Niacin group which the add of 60 mg kg-1 and 90 mg kg-1 was significantly lower than control group (P<0.05). The results showed that index of control group was increased significantly after heat stress (P<0.05), and reached the peak after 6h,6h and 3h respectively. Niacin group which the add of 60 mg kg-1 and 90 mg kg-1 was significantly lower than control group (P<0.05). Therefore, appropriate dietary niacin can effectively relieve plasma COR, ALT and AST levels after transport stress and acute heat stress on juvenile blunt snout bream, and option niacin addition of 60 mg kg-1 gave the best results.