ABSTRACT The effects of salinity, Na/K ratio and their interaction on growth, molting, nutrient retention and food conversion of Litopenaeus vannamei were investigated. The test shrimp were reared in artificial seawater and fed fresh polychaete worms, Neanthes japonica (Izuka) for 30 days. Two salinities (30 and 15 ppt) and 5 Na/K ratios (25.6, 34.1, 47.3, 102.1 and 153.3, retool/retool) were set, and each treatment had four replicates. During the feeding trial, the molting frequency (MF) was affected by neither salinity nor interaction effects, but Na/K ratio had an effect (P <0.05), but no significant differences in growth were found among treatments at 15 ppt (P> ... <0.05). At 15 ppt, no significant differences in FCE among treatments were found (P>

<0.05), yet no significant differences in final body weight were found between shrimp exposed to the latter four ratios (P><0.05). Na/K ratio showed no effects on shrimp final body weight at 15 ppt (P><0.05). However, no significant differences were in WG among Na/K ratios at salinity 15 ppt (P><0.05). Although no significant difference in FR was found among Na/K ratios at salinity 15 ppt (P><0.05), whereas salinity showed no significant influence (P><0.05), and no significant differences in PR were found between the latter 4 treatments (P><0.05). However, no significant differences in shrimp FCE were found among different Na/K ratios at salinity 15 ppt (P><0.05) and then declined a little at Na/K ratio 47.3 (P><0.05), but it should be noted that good growth had always been obtained under Na/K ratio 34.1 and 47.3 at both salinities. At salinity 15 ppt, no significant effects were found in growth between treatments of different Na/K ratios (P>

<0.05); NS, not 
significant (P><0.05). Means at the same Na/K ratio level were compared between 
salinity 30 and 15 ppt, an (*) following the means indicates 
significant difference (P><0.05); NS, not 
significant (P>