| The present study was performed to investigate the effects of dietary lipid on thebiochemical parameters and fatty acid composition of GIFT tilapia (Oreochromis niloticus)under cold stress. The results can be summarized as follows:1. The aim of this study was to identify the physiological changes and resistance ofGIFT tilapia (Oreochromis niloticus) under cold stress.75fish (average body weight103.0±1g) were randomly distributed into3glass tanks (80cm×45cm×45cm) of theeco-circulating system. The experimental tilapia was acclimated at28℃as an initialcontrol and then the water temperature was reduced from28℃to15℃at a rate of1℃/h.For monitoring the responses under cold stress, blood, liver and muscle samples werecollected on0,0.5,1,2,3and5day after exposed to15℃.The results showed that theserum K+increased significantly, Na+and Cl-decreased significantly, Ca2+concentrationwas instability under cold stress. Glucose rapidly increasing when the temperature wasdrop at15℃and followed by a declining trend approaching the original level, even fell toa lower level. A reduction was found in serum lipids including triglyceride (TG),cholesterol (CHOL), low density lipoprotein-cholesterol (LDL-C) under cold stress but nodifferences (P>0.05) except for TG. High density lipoprotein-cholesterol (HDL-C) showedan increasing trend and gradually reduced during cold stress (P<0.05). Aspartateaminotransferase (AST) activities were prominently elevated as the result of cold stress(P<0.05). Alanine aminotransferase (ALT) activities displayed an increasing trend andgradually reduced during cold stress (P<0.05). Hepatic superoxide dismutase (SOD) andcatalase (CAT) activities showed a remarkable rise on day0.5under the cold stress(P<0.05), and gradually decreased thereafter until the end of experiment. Real-timequantitative PCR showed that heat shock protein70(HSP70) mRNA level was induced bycold stress. A maximum of HSP70mRNA level was displayed on day0.5of exposed timeboth in liver and muscle of tilapia (P<0.05).Serum biochemical indices, activities of antioxidant enzymes and the expression ofHSP70mRNA were significantly affected by cold stress. These indices can be used as theuseful tool to monitor the physiological changes and resistance of GIFT tilapia(Oreochromis niloticus) under cold stress. 2. A feeding experiment was conducted to investigate the dietary lipid level on thebiochemical parameters and fatty acid composition of GIFT tilapia (Oreochromis niloticus)under cold stress. Fish (average body weight37.0±1g)were fed diets containing fourgraded lipid levels (1.95%,6.19%,8.03%,9.95%) which were supplemented with0%,4%,6%,8%of soybean oil in basal diet (1.95%lipid) for8weeks. After feeding experiment,the fish were acclimated at28℃as an initial control and then the water temperature wasreduced from28℃to15℃at a rate of1℃/h.The results showed that the survival rateranged from97.33%to98.67%and feed coefficient (1.37-1.46) with no significantdifferences among dietary treatments (P>0.05) after feeding experiment. The weight gainrate and specific growth rate increased with dietary lipid level increasing (P<0.05). Crudeprotein of whole body decreased significantly (P<0.05) and crude protein of muscle had nosignificant effected with dietary lipid level (P>0.05). Crude lipid of whole body andmuscle raised significantly with dietary lipid level (P<0.05). Crude ash of whole bodydecreased significantly, Crude ash of muscle increase and decreased afterward. Moisture ofwhole body and muscle were not significant effected by dietary lipid level (P>0.05).Under cold stress, GLU, total protein (TP), TG, CHOL, LDL-C raised significantlywhen dietary lipid level increasing (P<0.05). HDL-C showed an increasing trend andgradually reduced when dietary lipid level increasing (P<0.05). Transaminase (AST, ALT)in serum slightly decreased and increased significantly with dietary lipid level increasing(P<0.05). SOD activities decreased significantly,1.95%and6.19%group significantlyhigher than9.95%group (P<0.05), CAT activities had a trend of going up first then fallingdown with1.95%,6.19%and8.03%group significantly higher than9.95%group (P<0.05).On the base of control, a maximum of HSP70mRNA level was displayed (P<0.05) whendietary lipid level reach6.19%, HSP70mRNA level in liver of6.19%group significantlyhigher than8.03%and9.95%group, while HSP70mRNA level in muscle of6.19%grouphigher than8.03%group. With dietary lipid level increasing, the proportion of DHA, EPAslightly decreased, the saturated fatty acid (SFA) proportion of liver showed a decreasingtrend and unsaturated fatty acid (UFA)proportion showed an increasing trend, but obviousvolatility was found in SFA and UFA proportion of muscle. Dietary lipid level hadsignificantly influence on∑n-3PUFA、∑n-6PUFA proportion and∑n-3/∑n-6ratio of liverand muscle(P<0.05).The growth performance, physiological function and fatty acid composition of GIFTwere significantly influenced by dietary lipid level. To elevate the growth and coldresistance ability of GIFT tilapia, the optimal level of dietary lipid were6.19%. And thehigher dietary lipid, the lower growth performance was indicated in this work. 3. A feeding experiment was conducted to investigate the dietary lipid sources on thebiochemical parameters and fatty acid composition of GIFT tilapia (Oreochromis niloticus)under cold stress. Fish (average body weight40.0±1g) were fed diets containing four lipidsources (soybean oil, SO; soy oil: fish oil=1:1, SFO; soybean oil: lard oil=2:1, SLO;soybean oil: fish oil: lard oil=1:1:1, SFLO) for8weeks. After feeding experiment, fishwere acclimated at28℃as an initial control and then the water temperature was reducedfrom28℃to15℃at a rate of1℃/h.The results showed that the survival rate amongtreatments were not significantly different (P>0.05). Feed coefficient ratio of SO wassignificantly lower than that of other treatments (P<0.05). Crude protein of whole body inSO and SFO were significantly higher than that of other groups (P<0.05) and crude proteinof muscle had no significant differences in dietary groups (P>0.05). Crude lipid of wholebody in SO was the highest and the lowest one in SFLO, meanwhile crude lipid of musclein SFO was the highest and the lowest one in SFLO with significant differences amonggroups(P<0.05). Crude ash of whole body in SO and SFO were significantly higher thanthat of other groups (P<0.05) and crude protein of muscle had no significant differences indietary groups (P>0.05). Moisture of whole body and muscle were not significant effectedby dietary lipid sources (P>0.05).Under cold stress, there were significant influence of TG, CHOL, HDL-C,transaminase (AST, ALT)(P<0.05) and GLU, TP, LDL-C were not significantly effected bydietary lipid sources(P>0.05). The SOD activities in SO were significantly higher thanthose of other groups, the CAT activities in SO were significantly higher than those in SLOand SFLO(P<0.05). On the base of control, the SFO group displayed a maximum ofHSP70mRNA level, which was significantly higher than that of other groups (P<0.05).Fatty acids proportion of muscle and liver had significant correlation with fatty acidsproportion in dietary. The proportion of DHA, EPA in SFO and SFLO were obviouslyhigher than those of SLO and SO groups, especially in SFO group (P<0.05). The SFAproportion of liver and muscle in SO and SFO showed relative low value, while UFAproportion were relatively higher than other groups. Dietary lipid sources had significantlyinfluence on∑n-3PUFA、∑n-6PUFA proportion and∑n-3/∑n-6ratio(P<0.05).The growth performance, physiological function and fatty acid composition of GIFTwere significantly influenced by dietary lipid sources. According to serum biochemicalindices, elevated activities of antioxidant enzymes (SOD, CAT), the expression of HSP70mRNA, SFO(soybean oil:fish oil=1:1) could promote lipid metabolism, while elevatingantioxidant enzyme activities and HSP70mRNA, regulating the SFA and UFA proportionin tilapia,and these were benefit to growth and cold resistance ability of GIFT tilapia. |
PDF Full Text Request