Opercular ventilation and tail beat frequency of manacron-exposed Clarias gariepinus (Burch. 1822)
Clarias gariepinus (mean total length, 3.309±0.49cm SD; mean weight, 2.24±0.51g SD) were exposed in groups often fish per aquarium in triplicates to 20/ of sublethal concentrations (0, 9, 12, 14, 16 and 18mg/l) of monocron (dimethylphosphate-3- hydroxy-N-methyl-cis-crotonamide) for 96hrs in a renewable static bioassay. The fish manifested abnormal behaviours such as gulping for air at the surface and dash movement on placements in the solutions. Opercular ventilation rate was more responsive to the toxicant than tail beat. However, the response was not directly related to the concentration of the toxicant. The opercular ventilation differed considerably (p < 0.01) with the concentrations of the toxicant, but did not vary with the time of exposure (p <0.05). The dorsal fins of exposed fish showed rippling movements which rate appeared to be concentrations dependent. Tail beat frequency was more depressed after the 24th hr in all the exposure concentrations below that in the control. The tail beat frequency decreased (p < 0. OOI) with increasing concentration of the monocron but not with the exposure time (p > 0.05). Results from this study suggest that monocron affected the physiology of exposed fish possible through impaired nerve impulse transmission as demonstrated in the altered behaviour of the exposed fish.
Key words: Opercular ventilation, tail beat frequency, monocron, Clarias gariepinus