title: Dietary sodium requirement determined for juvenile hybrid tilapia (Oreochromis niloticus x O. aureus) reared in fresh water and seawater.
abstract: Two 8-week feeding trials were conducted to determine the dietary Na requirement for juvenile hybrid tilapia (Oreochromis niloticus x O. aureus) reared in fresh water and seawater. In each experiment, NaCl was added to the basal diet at 0, 0.5, 1, 2, 3, 5, or 7 g Na/kg diet (fresh water) and at 0, 0.2, 0.5, 0.8, 1.2, 1.5, 2, or 3 g Na/kg diet (seawater). Each diet was fed to three replicate groups of fish, individual fish initially weighing 0.69 (se 0.01) g, in a closed, recirculating rearing system. In fresh water, the tilapia fed the diet supplemented with 2 g Na/kg diet had significantly (P<0.05) greater weight gain than the fish fed the diets supplemented with >/=3 and </=0.5 g Na/kg diet. Feed efficiency (FE) in fish generally followed the weight-gain pattern. Gill Na(+)-K(+) ATPase activity was highest in the fish fed the diets supplemented with 1-3 g Na/kg diet, followed by the fish fed the diet with 7 g Na/kg diet and lowest in the fish fed the unsupplemented control diet. In seawater, the weight gain, FE and gill Na(+)-K(+) ATPase activity in fish were not affected by the dietary treatment. Analysis by polynomial regression of weight gain, by broken-line regression of gill Na(+)-K(+) ATPase activity and by linear regression of whole-body Na retention of the fish reared in fresh water, indicated that the adequate dietary Na concentration for tilapia is about 1.5 g/kg diet. The present study also suggests that no dietary Na is required for tilapia reared in seawater.
authors.affiliation: Department of Food Science, National Taiwan Ocean University, Keelung 202, Taiwan. syshiau@mail.ntou.edu.tw
authors.forename: Shi-Yen
authors.initials: SY
authors.lastname: Shiau
authors.forename: Li-Shan
authors.initials: LS
authors.lastname: Lu
mesh_terms: D000704:Analysis of Variance; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D004032:Diet; D004305:Dose-Response Relationship, Drug; D005398:Fisheries; D005618:Fresh Water; D005880:Gills / Q000201:enzymology; D008297:Male; D012623:Seawater; D012982:Sodium, Dietary / Q000008:administration & dosage* / Q000494:pharmacology; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D015996:Survival Rate; D017210:Tilapia / Q000254:growth & development* / Q000378:metabolism; D015430:Weight Gain / Q000187:drug effects
chemical_list: D012982:Sodium, Dietary; D000254:Sodium-Potassium-Exchanging ATPase