Impact of fertilizer (urea) on oxygen consumption and feeding energetics in the fresh water fish Oreochromis mossambicus

The effects of urea on survival, food utilization and oxygen consumption of the fresh water fish Oreochromis mossambicus were studied. The percentage survival of O. mossambicus when exposed to different concentrations of urea at 24, 48, 72 and 96 h exposures was noted and it was found that 22,000 and 38,000 mg L −1 urea concentration were sublethal and lethal, respectively. The median lethal concentration, which killed 50% of the fishes during 96 h exposure, was 28,000 mg L −1. Rearing the fish in increasing sublethal concentrations of urea, it was found that the feeding rate decreased from 34.341 ± 7.067 mg g live fish −1 d −1 (control) to 13.921 ± 2.315 mg g live fish −1 d −1 at the highest concentration of urea (22,000 mg L −1). Growth rate was drastically reduced. The consumption of oxygen in O. mossambicus diminished from 0.962 ± 0.208 to 0.645 ± 0.118 mg g live fish −1 h −1 when reared in the highest sublethal concentration of urea.