Growth Responses of Oreochromis niloticus Exposed to Sub-lethal Concentrations of Industrial Effluent from Agbara Environs of Ologe lagoon, Lagos, Nigeria

Aims: The present study is on the toxicity of sub-lethal concentrations of industrial effluents (IE) on the growth responses of Oreochromis niloticus (fingerlings and juveniles) from the Agbara environs of Ologe Lagoon, Lagos state, Nigeria.

Study Design: The culture system was a static renewable bioassay and was carried out in the fisheries laboratory of the Lagos State University, Ojo-Lagos, Nigeria. The fish were cultured in varying concentrations of industrial effluents: 0% (control), 5%, 15%, 25%, and 35%. Trials were carried out in triplicates for twelve (12) weeks.

Methodology: Weekly physico-chemical parameters: temperature (0C), pH, conductivity (ms/cm) and dissolved oxygen (DO in mg/l) were measured in each treatment tank. Length (cm) and weight (g) data were obtained and used to calculate various growth parameters: mean weight gain (MWG), percentage weight gain (PWG), daily weight gain (DWG), specific growth rate (SGR) and survival.

Results: The physico-chemical parameters showed that the pH of the culture water for O. niloticus fingerlings ranged from 7.57 – 7.97 and 7.86 – 7.97 for juveniles. DO results ranged from 2.89 - 4.72 mg/l for fingerlings and 4.54 - 7.68mg/l for juveniles. There were significant differences (P<0.05) in the DO values among the culture water. The DO values decreased with increase in effluent concentration for all treatments. The mean conductivity values obtained ranged from 0.51 – 0.53 ms/cm and 0.35 – 0.42 ms/cm for fingerlings and juveniles respectively. The temperature was stable throughout the study period; it ranged from 27.9 – 28.120C and 23.94 – 27.140C respectively. There was progressive increase in length and weight of fish during the culture period. The fish placed in the control had the highest increase in both weight and length, while fish in 35% had the least. MWG ranged from 5.15 – 8.8 and 4.48 – 15.2, DWG is from 0.14 – 0.19 and 0.52 – 0.64, PWG varied from 42.53 – 54.17 and 10.36 – 28.38, SGR ranged from 0.69 – 0.93 and 0.13 – 0.39 for fingerlings and juveniles respectively.

Conclusion: This study had shown that the industrial effluents from study site affected the health status of the test organisms, the water quality parameters (especially oxygen content), and impaired the growth of both the fingerlings and juveniles of O. niloticus when exposure continued for a long period of time.