Abstract
Sublethal effects of various concentrations of fertilizer effluents on the tail beat frequency per minute (TBF min.-1) and opercular beat frequency per minute. (OBF min-1) of Orechromis niloticus, Clarias gariepinus and hybrid (Heterobranchus bidorsalis (female) x C. gariepinus (male)) were examined in a static 96hr. bioassay under laboratory conditions. Effluent concentration, ammmonia (ionised and un-ionised), urea and pH significantly affected TBF and OBF of the three species. Ammonia particularly, the un-ionised form exacted the most significant effect onTBF and OBF. OBF appears be a more sensitive indicator of stress than TBF and may therefore be more suitable for detecting sublethal physiological effects of pollutants. This study further revealed that the fertilizer effluents have variable compositions whose values may far exceed the allowable limits and hence may pose great danger to the aquaticenvironment.
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