Effect Of Dietary Potassium Level On Growth And Physiological Characteristics Of Shrimp, Litopenaeus Vannamei, Reared In Three Different Waters

Three 8-week feeding trials were conducted to evaluate the effects of different levels of dietary potassium (K~+) on growth, nitrogen metabolism, osmoregulation and immunity of pacific white shrimp (L.vannamei) reared in different waters (sea water, dilute seawater, artificial water with 40 Na~+/K~+ ratios). A basal diet contained 0.59% K~+ was supplemented with 0.0%, 0.3%, 0.6%, 0.9%, 1.2%, 1.5% K~+ to formulate six experimental diets and shrimp were feed each diet for eight weeks. The results can be briefly summarized as follows:1. Shrimp reared in sea water and fed diets with 0.0%-0.6% K~+ supplementation showed significantly higher weight gain rate (WGR), specific growth rate (SGR), protein efficiency ratio (PER) and lower feed conversion ratio (FCR) than those of the others (P<0.05). Survival of shrimp for all dietary treatments ranged from 97.5% to 100%, and there were no significant differents among them (P>0.05). Dietary potassium (K~+) level significantly affected the body potassium (K~+), protein, lipid concentration of shrimp (P<0.05), however, body moisture and ash were not significantly affected (P>0.05). Shrimp fed diets supplemented with 0.3%-1.5% K~+ diets showed significantly lower (P<0.05) ammonia-N excretion rate than that of the basal diets. The concentrations of hemolymph K~+ and Na~+ were not significantly affected by dietary K~+ levels. However, the hemolymph osmolality and Cl~- concentration of shrimp fed with diets supplemented of 0.6%-1.5% K~+ were significantly higher than that of the basal diet (P<0.05). The gill Na~+-K~+-ATPase activity and serum total protein concentration all revealed a significant peak change with increase of K~+ supplement (P<0.05), the Na~+-K~+-ATPase activity of 0.3% K~+ group was highest in all treatments. Supplementations of 0.3-1.5% K~+ showed significantly higher total haemocyte count (THC) and O2-production than those of the basal diet. In addition, the phenoloxidase (PO) and lysozyme (LSM) of 0.3% K~+ treatments were highest in all treatments. In conclusion, the supplement of dietary 0.3% K~+ (total 0.96g/100g K~+ in diet) may be propitious to improve the growth of L.vannamei reared in sea water and enhance the physiological acclimation of organism. And, dietary potassium (K~+) level more than 1.48g/100g (0.9% group) will inhibit the growth of shrimp. 2. Shrimp reared in low salinity dilute seawater (4) and fed diets with 0.9% K~+ supplementation showed significantly higher weight gain rate (WGR),specific growth rate (SGR) and protein efficiency ratio (PER) than those of the basal diets (P<0.05). Survival, feed conversion ratio (FCR), body moisture, lipid, ash, protein contents were not significantly affected by dietary potassium (K~+) levels. However, body potassium (K~+) concentration of shrimps fed with diets supplemented with 0.3%-0.9% K~+ were significantly higher than that of other treatments (P<0.05). Shrimps fed diets supplemented with 0.9% K~+ showed significantly lower (P<0.05) ammonia-N excretion rate than that of those fed the basal diets. The hemolymph arginase activity levels was increased significantly in comparison with increasing levels of dietary K~+ (P<0.05).The urea concentration revealed a significant peak change with increase of K~+ supplement (P<0.05),and urea concentration of 0.9% K~+ group were highest in all treatments. The contents of hemolymph K~+ and hemolymph osmolality were not significantly affected by dietary K~+ levels. But, hemolymph Na~+ and Cl~- concentration of shrimp fed with diets supplemented of 0.6%-0.9% K~+ were significantly lower than those of the basal diet (P<0.05).The gill Na~+-K~+-ATPase activity revealed a significant peak change with increasing of K~+ supplement (P<0.05), and the gill Na~+-K~+-ATPase activity of 0.9% K~+ group were highest in all treatments. The hemocyanin concentration, O2- production, phenoloxidase activity (PO) and superoxide dismutase activity (SOD) of 0.9% K~+ group were highest in all treatments.Lysozyme activity (LSM) with 0.9%-1.5% K~+ treatments were significantly higher than that of others (P<0.05). The result of challenge indicated that the cumulative mortality of shrimp of 0.3% K~+ group were significantly lower than that of the basal diet (P<0.05)in the 7th day. There were no significantly different of the cumulative mortality among 0.3%-0.9% K~+ groups (P>0.05). In conclusion, the supplement of dietary 0.9% K~+ (total 1.48g/100g K~+ group in diet) may be propitious to improve the growth of L.vannamei reared in low salinity seawater and enhance the physiological acclimation of organism.3. Shrimp,which cultured in the artificial low salinity water and Na/K=40,of 0.6% K~+ group showed significantly highest weight gain rate (WGR) than that of the other treatments(P<0.05). The body potassium (K~+) and protein efficiency ratio (PER) of 0.3% K~+ group were highest in all treatments. Ammonia-N excretion rate of shrimp of 0.6% K~+ group and oxygen consumption rate of 0.9% K~+ group were significantly lowest than those of the basal diet (P<0.05).The hemolymph arginase activity levels increased significantly with increasing dietary potassium (P<0.05). Hemolymph Na~+ and Cl~- concentration of shrimps fed with diets supplemented of 0.3% K~+ group were significantly lowest than those of the others (P<0.05). The gill Na~+-K~+-ATPase activity revealed a significant peak change with increase of K~+ supplement (P<0.05), and the Na~+-K~+-ATPase activity of 0.6% and 0.9% K~+ groups were highest in all treatments. Dietary potassium (K~+) levels not significantly affected the hemolymph osmolality and K~+ concentration of shrimps (P>0.05). The phenoloxidase (PO) and lysozyme (LSM) of 0.3% and 0.6% K~+ groups and the O2- production and phenoloxidase activity (PO) of 1.2% K~+ group were highest in all treatments. There were no significantly difference of the O2- production and phenoloxidase activity (PO) among 0.3%-1.2% K~+ groups (P>0.05).Hemocyanin concentration of 0.6% K~+ group was highest in all treatments. Lysozyme activity (LSM) and superoxide dismutase activity (SOD) of 0.3% and 0.6% K~+ groups were significantly higher than that of the basal diet (P<0.05). In conclusion, the supplement of dietary 0.3% K~+ (total 0.96g/100g K~+ in diet)-0.6% (total 1.26g/100g K~+ in diet) K~+ may be propitious to improve the growth of L.vannamei reared in artificial low salinity water (Na~+/K~+ ratios =40) and enhance the physiological acclimation of organism.