Sublethal Effects of Ammoniacal Fertilizer Effluents on three Commercial Fish Species from Niger Delta Area, Nigeria

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 on TBF 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 aquatic environment. Aquatic pollution is significant to fisheries and aquaculture industries. Studies have been conducted on the toxic effects of effluents (waste waters) on various commercial fish species (Wai-Ogosu 1987, Ojuola and Onuoha, 1987). Some of such studies were done with increasing interest in finding physiologic correlate of activity that can be monitored under field conditions (Thorpe, 1987). Investigations into the relationship of such parameters as heart rate, tail beat frequency and respiration rate with activity have been attempted (Ross et al. 1981). Changes in opercular rhythm have been documented as sensitive indicator of physiological stress in fish subjected to sublethal levels of pollutants (Davis, 1973). However, none of the above dealt with the toxicity of ammoniacal fertilizer effluents on tilapia and Clarias species which are common estuarine and pond – reared fish in Africa. This study investigates the sublethal effects of wastewater from a fertilizer company in the Niger Delta area of Nigeria on the tail beat frequency (TBF) and opercular beat frequency (OBF) of fingerlings of three commercial fish species – Oreochromis niloticus, Clarias gariepinus and hybrid (Heterobranchus bidorsalis (female) x C. gariepinus (male)). The information obtained from this study would be helpful in predicting the effect of effluent in the field