Effects of aqueous Na/K and dietary K on growth and physiological characters of the Pacific white shrimp, L itopenaeus vannamei , reared in low‐salt well water

The synchronous effects of aqueous Na/K and dietary potassium (K + ) on growth and physiological characters was studied on the Pacific white shrimp ( L itopenaeus vannamei ) reared in low‐salinity well water (4 ppt) for 8 weeks with initial weight of 0.28 ± 0.01 g. Three practical diets were formulated with supplement of 0, 0.3%, 0.6% K + which contained 1.29 g/100 g, 1.60 g/100 g, 1.93 g/100 g K + respectively. The supplement of K + to the low‐salinity well water was 10, 20, 40 mg L −1 which formed Na:K ratios of 42:1, 33:1, 23:1 respectively. Results showed that when the aqueous Na:K ratio was 42 and dietary K + was 1.93 g/100 g K + , the WGR and PER of L. vannamei were the highest and the FCR was lower than that of others ( P  < 0.01). Supplement of K + into well water and diets did not showed significant effects on haemolymph ammonia‐N, uric acid, urea content ( P  > 0.05), but had a extremely significant effect on arginase activity and Cl − concentration ( P  < 0.01). Moreover, similar results were observed in alkaline phosphatase (ALP), bacteriolytic activity (LSZ) and respiratory burst activity (O 2 − ) ( P  < 0.05). These results suggested that aqueous Na/K in the low‐salt well water and dietary K had significant synergistic effect on the growth, osmoregulation and immunity of L. vannamei . Concluded from the growth performance, nitrogen metabolism, osmoregulation and immunity, as the Na/K in the low‐salinity well water descended from 42 to 23, the requirement of dietary K + was also decreased.