Evaluation of sodium chloride (NaCl) for potential prophylactic treatment and its short-term toxicity to African catfish Clarias gariepinus (Burchell 1822) yolk-sac and swim-up fry

Disease and parasite outbreaks cause mortality of fish, affecting mostly early stages of fish cycle. The outbreaks are usually prevented using a number of chemicals including salt (NaCl) for which protocols are lacking. The purpose of this study was to determine the efficacy of NaCl as a potential prophylactic treatment and its short term toxicity on African catfish (Clarias gariepinus) yolk-sac and swim-up fry during a 24 h exposure period. Three-day-old yolk sac and six-day-old swim-up fry (n = 50 for each stage) were subjected to static bath dip treatment in increasing concentrations of NaCl (0.1, 0.2, 0.4, 0.8, 1.0, 2.0, 4.0, and 10.0 g/L) for 15, 30 and 60 min. Toxic ranges were tested by exposing the fry stages to concentrations of 0.25, 0.5, 0.75, 1.0, 1.25, and 1.50 g/L NaCl for 24 h. Controls were not subjected to any concentration of NaCl. All experiments were executed in triplicate. Regardless of the concentrations and duration of exposure, survival of fish in NaCl treatment differed significantly (P < 0.05) from the untreated controls. Effective concentration ranges of NaCl were 0.2–0.8 g/L and 0.2–1.0 g/L in the yolk sac and swim-up fry respectively at exposure duration of 15 min. No fry survival was recorded at a concentration of 10.0 g/L for either stage of development. The mean 24 h LC50 values for the yolk sac and swim-up fry were 0.61 and 0.70 g/L NaCl respectively. Sodium chloride may be used as prophylactic treatment in early stages of C. gariepinus but could be toxic at longer exposure times. However, empirical tests on efficacy of NaCl on pathogens are recommended.