| The purpose of this study was to investigate the optimum dietary niacin and vitamin C requirement for GIFT tilapia of two different growth stages. The effects of dietary niacin and vitamin C on growth performance, body composition, several serum parameters and liver vitamin accumulation of GIFT tilapia were also estimated. The contents and results of this study are as follows:(1) The dietary niacin requirement of GIFT Tilapia (220-500g)Total360GIFT tilapia (Oreochromis niloticus) with average initial body weigh of (220.2±7.7)g were randomly distributed into6groups consisting of3replicates (20fish per net). Each group was fed a diet with niacin levels were11.8(basal diet),37.8,64.7,89.4,157.2,335.4mg·kg-1for10weeks. Growth, feed utilization, body composition, some serum biochemical indices and liver niacin concentration were measured to detect the suitable requirement of niacin in diet of GIFT tilapia. The results showed that, the addition of niacin to diets significantly improved fish weight gain rate and feed efficiency (P<0.05). The crude protein content in whole-body of fish in the157.2mg·kg-1and335.4mg·kg-1groups was significantly higher than other groups (P<0.05); the crude lipid content of fish in the64.7mg·kg-1group was highest, significantly higher than the unsupplemented group (P<0.05); no significant differences were existed in moisture and ash of the fish (P>0.05). The serum total cholesterol, high density lipoprotein cholesterol and total protein content first increased then decreased as the level of dietary niacin increased, they were reached to the peak when fish fed diet containing157.2mg·kg-1niacin. The addition of niacin to diets significantly reduced serum triglyceride content (P<0.05). The niacin content in liver first increased then plateaued with increasing dietary niacin levels and it was significantly higher in the niacin added groups than that in the control group (P<0.05). Regression analysis showed that GIFT tilapia need63.6mg·kg-1,158.5mg·kg-1and172.4mg·kg-1niacin based on maximum weight gain rate, niacin content in liver and serum high density lipoprotein cholesterol content, respectively.(2) The dietary niacin requirement of GIFT Tilapia (80-350g)Six semi-purified diets were formulated to contain graded level of niacin (6.4(basal diet),16.8,36.8,68.5,143.8,297.8mg·kg-1, respectively). Each diet was fed to triplicate groups of30GIFT tilapia(Oreochromis niloticus)(initial average weight87.2±3.3g) for12weeks in5.6-m aquaria(r=1.5m, h=0.8m). Results showed that, dietary niacin supplementation significantly improved the growth of GIFT tilapia (P<0.05), weight gain rate of fish increased linearly with dietary niacin levels (from6.4mg·kg-1to20.4mg·kg-1), but remained unchanged at higher supplementations (P>0.05). The special weight gain rate showed a similar pattern to the weight gain rate. Niacin concentrations in fish livers were positively correlated with dietary levels of niacin and plateaued when niacin in diet exceed84.6mg·kg-1. Liver niacin concentrations of fish in the last two high supplement groups were significantly higher (P<0.05) than that of the other four group which had significant differences between each other (P<0.05). Serum high density lipoprotein cholesterol contents increased linearly with the increasing of dietary niacin level. Contents of serum triacylglycerol and activities of serum aspartate aminotransferase and alanine aminotransferase significantly decreased (P<0.05). Serum alkaline phosphatase activities of fish first increased then decreased and it was highest in the fish fed diet with36.8mg·kg-1niacin. There were no significant differences on serum glucose and total cholesterol contents of fish in the separate fish groups (P>0.05). Broken-line regression analysis showed that GIFT tilapia requires a minimum of20.4mg·kg-1niacin in the diet for maximal growth, and has the highest liver niacin accumulation at a dietary level of84.6mg·kg-1.(3) The dietary vitamin C requirement of GIFT tilapia (220～550g)Three repeat groups of experimental GIFT tilapia Oreochromis niloticus with initial body weight (220.1±6.1)g were cultured in net cages(20fish each cage) and fed by semi-purified diets with six levels of vitamin C (17.3(basal diet),33.6,56.1,102.5,200.8and399.5mg·kg-1, supplied as L-ascorbyl-2-polyphosphate) for10weeks. Growth, body composition, some serum biochemical indices, vitamin C concentration in liver and musle of fish were measured at the end of trial. The results showed that, No L-gulonolactone oxidase was detected in the kidney and liver of tilapia. Supplying vitamin C to diets significantly improved tilapia weight gain rate and specific growth rate (P<0.05). The supplement of vitamin C to diets had no significant influence on the feed efficiency and body composition of tilapia (P>0.05). The vitamin C contents in liver and musle of tilapia first increased then plateaued with increasing dietary vitamin C levels. The vitamin C contents in the liver of the fish fed200.8and399.5mg·kg-1vitamin C were significantly higher than that of fish fed the other diets (P<0.05). The vitamin C content in the liver of the fish fed102.5mg vitamin C per kg diet was significant higher than that of fish of the lower vitamin C added groups (P<0.05). The vitamin C contents in the musle of the fish fed200.8and399.5mg·kg-1vitamin C were significant higher than that of the fish of 33.61mg·kg-1vitamin C group and control group (P<0.05). Above all, it concluded vitamin C is necessary for the growth of GIFT tilapia. Regression analysis showed that the dietary vitamin C requirement of it was estimated to60.4mg·kg-1for optimum growth, and197.1mg·kg-1and205.2mg·kg-1diet for maximum liver and musle vitamin C concentration, respectively.(4) The dietary vitamin C requirement of GIFT tilapia (70-300g)Triplicate groups of experimental GIFT tilapia Oreochromis niloticus with initial body weight (70.0±1.6)g were cultured in5.6-m3aquaria(r=1.5m, h=0.8m;25fish each aquaria) and fed by semi-purified diets with six levels of vitamin C (6.1(basal diet),23.8,41.9,85.1,167.4and339.0mg·kg-1diet, supplied as L-ascorbyl-2-polyphosphate) for12weeks. The results showed that, with increasing dietary vitamin C level, weight gain rate and specific growth rate of tilapia first increased then kept in stable, there were no significant difference between the first two groups (P>0.05), they were significantly lower than the other four groups (P<0.05). The contents of muscle collagen protein increased; the vitamin C contents in liver and musle of tilapia first increased then plateaued when dietary vitamin C levels increased. The contents of muscle collagen protein and the vitamin C contents in the liver and musle of the fish fed167.4mg·kg-1and339.0mg·kg-1vitamin C diet were significantly higher than that of fish fed the other diets (P<0.05). The supplementation of vitamin C in diet have significantly effect on the fat content of fish whole-body, serum alkaline phosphatese, the activities of serum aspartate aminotransferase and alanine aminotransferase (P<0.05). Serum albumin content first increased then decreased, it was highest in the167.4mg·kg-1group. Feed efficiency, moisture and protein content of the whole-body of fish and the content of hemoglobin had no significant difference among all the groups (P>0.05). Regression analysis showed that GIFT tilapia was estimated to need45.0mg·kg-1vitamin C in diet for optimum growth,114.9mg·kg-1and118.6mg·kg-1for maximum liver and musle vitamin C concentration, respectively.From above results, it suggested that the supplementation of niacin and vitamin C in diet are essential for the growth of GIFT tilapia. Dietary niacin could affect some serum lipid indices, the level of serum high-density lipoprotein cholesterol significantly increased, while the level of serum triglyceride significantly decreased; dietary vitamin C significantly increased serum alkaline phosphatase activity and muscle collagen content. there is a big difference on niacin and vitamin C requirement of GIFT tilapia between the two different growth stages, the requirements of the larger size fish were greater than that of the smaller size fish. |
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