Toxicity of nitrite to Nile tilapia: Effect of fish size and environmentalchloride

Small (4.4 +/- 1.50 g; mean +/- SD) Nile tilapias Oreochromis niloticus wer e more tolerant of nitrite than large (90.7 +/- 16.43 g) fish. The 96-h med ian lethal concentration of nitrite-N to small fish was 81 mg/ L (95% confi dence interval = 35-127 mg/L) compared with 8 mg/L (4-11 mg/L) for large fi sh. Addition of chloride to test water las either calcium chloride or sodiu m chloride) protected both small and large fish from nitrite. Sodium chlori de and calcium chloride appeared to be similarly effective in inhibiting ni trite toxicity.