Effect of Formalin on the Hatching Rate of eggs and Survival of larvae of the African Catish (<i>Clarias gariepinus</i>)

Abstract

The effect of formalin on the hatching rate of eggs of the African catfish and subsequent survival of the larvae were investigated using range finding and definitive tests to determine the impact of formalin for 15 minutes. In the range finding test, 0mgl^-1 (control), 250mgl^-1, 500 mgl^-1, 750 mgl^-1, and 1000 mgl^-1 of formalin were used to define the threshold limit of tolerance of eggs to formalin. There were significant differences in the hatching rate and survival of early larvae between the control and all four formalin concentrations (p<0.05). 500 mgl^-1, 750 mgl^{- 1}, and 1000 mgl^-1 of formalin resulted in total egg mortality (0% hatching rate). In the definitive test, the difference between the control and 50mgl-1, 100 mgl^-1, 150 mgl^-1, and 250 mgl^-1 of formalin was significant in hatching rate (p<0.05).There was no significant difference between 50mgl^-1, 100 mgl^-1, 150 mgl^-1 (p>0.05). The survival rate of early larvae of Clarias gariepinus showed no significant difference between the control and 50mgl^-1, 100 mgl^-1, 150 mgl^-1, and 250 mgl^-1 (p<0.05).In conclusion, formalin, although applied as a broad spectrum chemical in aquaculture in the treatment of fish disease, particularly fungi, as in this study, where it effectively reduced fungi on eggs and larvae of Clarias gariepinus, impacted negatively in terms of acute toxicity effect on the fish. Its use should be carefully investigated to reduce potential toxic effect on fish. @JASEM

J. Appl. Sci. Environ. Manage. December, 2010, Vol. 14 (4) 31 - 34