Effect Of Dietary Carbohydrate And Lipid Levels On Growth Performance And Physiological Status Of Japanese Seabass (Lateolabrax Japonicus) In Different Growth Stages

Four10-week feeding trials were conducted to examine the effectsof different dietary carbohydrate and lipid levels on growth performanceand physiological status of Japanese seabass, Lateolabrax japonicus, indifferent growth stages. The experiment of adult Japanese seabass wasconducted in indoor culture system (Volume120L) and the temperatureranged from16to24℃. The experiment of post-adult Japanese seabasswas conducted in seawater floating net cages (1.5m×1.5m×2.0m) and thetemperature ranged from19to24.5℃. Results of these studies arepresented as follows:1. Feeding trials were conducted to evaluate the effects of dietarycarbohydrate level on growth performance and physiological state ofJapanese seabass with average initial body weights (34.26±0.37) g and(343.3±1.0) g in adult and post-adult growth stage. Six isonitrogenousand isolipidic practical diets using fish meal and casein as proteinsources, corn starch as carbohydrate sources and fish oil as lipidsources were formulated to contain graded levels of carbohydrate (0，6，12，18，24and30%). The results showed that there were no significantdifferences in survival, condition factor (CF) and muscle glycogen of Japanese seabass at different growth stages among different levels ofcarbohydrate (P>0.05). In adult growth stage, the specific growth rate(SGR) and feed efficiency (FE) significantly increased first and thendecreased with the increasing of dietary carbohydrate (P<0.05). TheSGR of the fish fed the diet containing12%carbohydrate wassignificantly higher than that of24%and30%group (P<0.05) whileshowed no significant different with the diet containing18%carbohydrate (P>0.05). The FE of the fish fed the diet containing12%carbohydrate was significantly higher than that of control group(P<0.05). The hepatopancreas somatic index (HSI) and viscerosomaticindex (VSI) increased significantly with the increasing dietarycarbohydrate contents (P<0.05). The HSI of the fish fed the dietcontaining30%carbohydrate was significantly higher than that of0～18%group (P<0.05). The VSI of the fish fed the diet containing30%carbohydrate was significantly higher than that of12%group (P<0.05).The apparent digestibility coefficients (ADC) of dry matter and crudeprotein in diets reached highest at the starch level of18%and12%respectively in adult growth stage, which were significantly higherthan that of the control group (P<0.05). In post-adult growth stage, thespecific growth rate (SGR) and feed efficiency (FE) significantlyincreased first and then decreased (P<0.05). The SGR of the fish fedthe diet containing24%carbohydrate was significantly higher than that of0%，6%and12%group (P<0.05). The FE of the fish fed thediet containing18%carbohydrate was significantly higher than that ofcontrol group and6%group (P<0.05). The HSI of the fish fed the dietcontaining30%carbohydrate was significantly higher than that ofcontrol group (P<0.05). The VSI of the fish fed the diet containing12%carbohydrate was significantly higher than that of6%,18%and24%group (P<0.05). Serum glucose, plasma triglyceride, plasma totalcholesterol and liver glycogen were significantly affected by dietarydifferent carbohydrate at different growth stages (P>0.05). Nosignificant differences were observed in hexokinase (HK)(P>0.05) inadult stage while significantly affected in post-adult stage (P<0.05).In summary, diets containing a certain amount of carbohydrate (cornstarch) can promote the growth of Japanese seabass. The optimaldietary carbohydrate level for adult and post-adult Japanese seabass is17.75%and22.37%respectively. With the growth of Japanese seabass,the tolerance is getting stronger on carbohydrate.2. Feeding trials were conducted to evaluate the effects of dietary lipidlevel on growth performance and physiological state of Japaneseseabass with average initial body weights (34.26±0.37) g and(343.29±1.12) g in adult and post-adult growth stage. Fiveisonitrogenous and isoenergetic practical diets were formulated tocontain graded levels of lipid (0，4，8，12and16%). The results showed that no significant differences were observed in survival ofJapanese seabass in adult and post-adult growth stage among differentlevels of lipid (P>0.05). However, with the increasing of dietary lipidlevels, specific growth rate (SGR) and feed efficiency (FE)significantly increased first and then decreased with the increasing ofdietary lipid in different growth stage of Japanese seabass (P<0.05),and SGR reached highest at the lipid level of8%group, which wassignificantly higher than that of control group (P<0.05). In adultgrowth stage, the FE of the fish fed the diet containing8%lipid wassignificantly higher than that of12%and16%group (P<0.05), whilethe FE of the fish fed the diet containing12%lipid was significantlyhigher than that of control group and4%group (P<0.05) in post-adultgrowth stage. Serum glucose, plasma triglyceride, plasma totalcholesterol and malate dehydrogenase (MDH) were significantlyaffected by dietary different lipid at different growth stages (P>0.05).In adult growth stage, dietary lipid level significantly increased serumglucose (P<0.05), the serum glucose and MDH of the fish fed the dietcontaining8%lipid was significantly higher than that of control group(P<0.05). The plasma total cholesterol of the fish fed the dietcontaining4%lipid was significantly higher than that of control groupand12%group (P<0.05). The plasma triglyceride of the fish fed thediet containing4%lipid was significantly higher than that of other groups (P<0.05). While in post-adult growth stage, serum glucosesignificantly increased with the increasing dietary lipid level (P<0.05),and reached highest at the lipid level of16%, which was significantlyhigher than the other groups (P<0.05). The plasma total cholesteroland MDH of the fish fed the diet containing8%lipid was significantlyhigher than that of control group (P<0.05). The plasma triglycerideand FE of the fish fed the diet containing12%lipid was significantlyhigher than that of0%and4%groups (P<0.05). The liver lipid weresignificantly affected by dietary lipid level at different growth stage(P<0.05). In adult growth stage, the liver lipid reached highest at thelipid level of16%, which was significantly higher than that at the lipidlevel of control group and4%group (P<0.05), while the liver lipid ofthe fish fed the diet containing12%lipid was significantly higher thanthat of0%,4%and8%groups (P<0.05) at post-adult growth stage. Insummary, diets containing a certain amount of lipid can promote thegrowth of Japanese seabass. The demand on lipid increased with thegrowth of Japanese seabass. The optimal dietary lipid level for thegrowth of adult Japanese seabass is7.22%, while the optimal dietarylipid level for post-adult is10.5%.