Effects Of Dietary Sodium And Potassium On Growth, Body Composition And Physiology Of Japanese Seabass Lateolabrax Japonicas

The present study evaluated the effects of dietary sodium or potassium on the survival rate,growth performance, antioxidant capacity of hepatopancreas and osmotic regulation of Japaneseseabass (Lateolabrax japonicus) in the freshwater. The general results in the trial were showed asfollows:1. Effects of dietary sodium on growth, antioxidant capacity of hepatopancreas and osmoticregulation of Japanese seabass (Lateolabrax japonicas) in freshwaterDiets supplemented different levels of sodium were fed to Japanese seabass (initial bodyweight were20.91±0.25g) of6groups for56days, respectively. The actual levels of sodium inthe diets are0.44%、0.51%、0.62%、0.77%、1.66%and3.48%. The results showed that dietaryNa significantly affected the survival rate of Japanese seabass (P<0.05), which in0.62%Nagroup was the highest (97.3%) and in3.48%Na group was the lowest (35.7%). With the increaseof dietary Na, WG, SGR, FE and PER increased and then decreased (P<0.05), and the maximumvalue was observed in0.62%Na group (P<0.05). The experiment was divided into two periods(1-28d and29-56d). With the increase of dietary Na, the activities of protease, lipase andamylase intestine increased and then decreased (P<0.05), and there were no significantdifferences between those two periods. The activities of SOD, CAT, GOT and GPT inhepatopancreas increased and then decreased, which in the previous period (1-28d) significantlylowered than that in the latter period (29-56d), but the MDA has the opposite trend. GillNa+/K+-ATP enzyme activity increased with increasing dietary Na from0.44%to3.48%, andthen decreased, and there were no significant differences between those two periods. Serumosmolality of1.66%Na group and3.48%Na group were lower than the others, but there wereno significant differences between the two periods (P>0.05). The results indicated that dietaryappropriate dietary Na can significantly improve the survival rate, growth and capacity ofosmoregulation of Lateolabrax japonicas.2. Effects of dietary potassium on growth, body composition and osmotic regulation of Japaneseseabass (Lateolabrax japonicas) in freshwaterDiets supplemented different levels of potassium were fed to Japanese seabass (initial bodyweight were10.8±0.01g) of6groups for56days, respectively. And the actual levels of diets are0.1269%、0.1853%、0.2348%、0.2787%、0.3189%and0.3877%. The results show that deficiencysymptom will occur, if dietary potassium level is less than0.19%.With the increasing dietary K, the survival rate increased promptly and then kept stable, weight gain (WG), specific growth rate(SGR), feed efficiency (FE) and protein efficiency ratio (PER) increased (P<0.05). Crude proteinand crude fat content of the fish body increased promptly and then kept stabilized withincreasing dietary K (P<0.05); while the moisture content had an opposite trend (P<0.05). Withthe increasing dietary K, the activities of protease, lipase and amylase in the intestine increased(P<0.05); the activities of alkaline phosphatase (AKP), catalase (CAT) and superoxide dismutase(T-SOD) in the hepatopancreas tend to be stable after significantly elevated (P<0.05), but themalondialdehyde (MDA) has the opposite trend (P<0.05); With the increasing dietary K, gillNa+/K+-ATP enzyme activity decreased (P<0.05), there were no significant differences amongthe serum osmolality of different groups (P>0.05); growth hormone (GH) and insulin likegrowth factor-1(IGF-1) concentration in the serum decreased significantly (P<0.05), whereasprolactin (PRL) concentration significantly increased (P<0.05). According to the results, whenthe dietary potassium level is less than0.19%, deficiency symptom of Lateolabrax japonicasoccurs, accompanied by decreased antioxidant capacity of the hepatopancreas. According to thegrowth performance, dietary potassium level should not be less than0.39%.