Screening Of Attractants In Fishmeal-Free Diet And Effects Of Vegetable Oil Replacing Fish Oil On Turbot(Scophthalmus Maximus L.)

Part 1: In this experiment,different feeding attractants were screened by the preference of juvenile turbot(Scophthalmus maximus L.)in fishmeal-free diet.Six experimental diets were formulated and the positive control(PC)diet was formulated with fishmeal and soy protein concentrate(SPC)as protein sources.The other five experimental diets contained SPC,fermented soybean meal,casein and gluten as protein sources.The negative control(NC)diet did not include any feeding stimulant(FS)whereas the other diets were supplemented with 0.02% Dimethyl-?-propiothetin(DMPT),0.5% mixture of disodium 5'-inosinate(5'-IMP·2Na)and sodium glutamate(at ratio 1:7,MX),2% squid extract(SE)and 2% yeast extract(YE)respectively.The diets were fed to the fish(initial body weight,41.24 ± 0.14 g)for 30 days.Final results showed that feeding rate was significantly increased in MX group(P<0.05)and fish fed MX diet had the highest total feed intake.There were no significant differences in crude protein,crude ash and moisture of whole body among all groups(P>0.05).Fish in diet PC and MX had significantly higher crude lipid content than that of other diets(P<0.05).The neuropeptide Y(NPY)m RNA expression in brain was significantly improved by MX(P<0.05)and no significant differences were observed in Orexin m RNA expression between PC and MX diet(P>0.05).The highest m RNA expression level of insulin-like growth factor I receptor(IGF-IR)was observed in PC diet(P<0.05)and there were no significant differences between PC and MX diet(P>0.05).No significant differences were found among all groups in the content of serum growth hormone(P>0.05).The results demonstrated that MX in fishmeal-free diet could promote feeding behavior and growth performance of juvenile turbot.Part 2: An eight-week feeding experiment was conducted to evaluate the total replacement of marine origin ingredients by plant-derived materials in diets for turbot(Scophthalmus maximus L.)(mean initial body weight,35.95±0.05 g).The Control diet contained both fishmeal and fish oil.The second contained non-fishmeal protein sources and fish oil(FO).The third contained non-fishmeal protein sources and canola oil plus essential fatty acids(CAN+EFA).The last included non-fishmeal protein sources and soybean oil plus microalgae(SOY+ALG).Each diet was randomly fed to triplicate tanks with 30 fish per tank.The results showed that fish fed diet SOY+ALG had better growth performance and exhibited no significant difference with the Control(P>0.05).The lipid efficiency ratio in Control and SOY+ALG was significantly higher than that in FO and CAN+EFA(P<0.05).Fish in group FO and CAN+EFA had significantly lower whole fish body lipid content than those in Control and SOY+ALG(P<0.05).Significantly higher digestive enzyme activities was observed in diet Control and SOY+ALG(P<0.05).Amino acid and fatty acid composition in whole fish body,dorsal muscle and liver was closely correlated with the diets.There was no significant difference among all groups in serum content of glucose and total protein(P<0.05).A significant increased level of serum triglycerid,total cholesterol and low density lipoprotein cholesterol was observed in diet CAN+EFA and SOY+ALG compared to Control(P<0.05),whereas a reverse trend was found in high density lipoprotein cholesterol(P<0.05).No significant difference was observed in serum aspartate aminotransferase level among all groups(P>0.05).Except the Control,the other diet was significantly increased in serum alanine aminotransferase level(P<0.05).There was no significant difference in serum acid phosphatase level among all groups(P>0.05),and a significant increased level of alkaline phosphatase was found in CAN+EFA and SOY+ALG compared to Control(P<0.05).The lysozyme activities of CAN+EFA and SOY+ALG were significantly lower than Control in serum(P<0.05).The serum superoxide dismutase,catalase,glutathione peroxidase activities and malondialdehyde content were observed no significant difference among all groups(P<0.05).Malondialdehyde content in liver of CAN+EFA was significantly higher than that in Control and catalase,glutathione peroxidase and lysozyme activities was significantly lower than Control(P<0.05).No significant difference was found between the Control and SOY+ALG in antioxidant enzyme activities except for catalase(P>0.05).No significant difference was observed among all groups in neuropeptide Y expression level(P>0.05).The insulin-like growth factor 1 expression level was significantly lower in group FO and CAN+EFA(P<0.05)but significantly higher in group SOY+ALG(P<0.05).The lipoprotein lipase expression level in group CAN+EFA and SOY+ALG was significantly increased(P<0.05).Expression level of peroxisome proliferator-activated receptor ? was significantly decreased in group FO,CAN+EFA and SOY+ALG(P<0.05).The carnitine palmitoyltransferase 1 expression level was significantly lower in SOY+ALG group(P<0.05)but significantly higher in FO(P<0.05).The expression level of sterol regulatory element-binding protein 1 and fatty acid synthase was significantly increased in SOY+ALG(P<0.05).These results suggested that dietary plant proteins with soybean oil and microalgae totally replacing fishmeal and fish oil for turbot exhibited better growth performance than diet CAN+EFA and plant derived stuffs actually induced a reduced growth performance and antioxidant ability fish,however different feed stuffs exhibited different effect on that.