Effect of textile factory effluent on otolith and somatic growth parameters in Clarias gariepinus
Are otolith parameters more sensitive than somatic indices in detecting stress conditions in fish? This question was investigated using juvenile-sized Clarias gariepinus in a 30-day exposure bioassay to a textile factory effluent. A series of static bioassays were initially conducted with concentrations of 0.00-40.00% and the 96hr LC50 value derived by probit analysis was 20.06%. Nominal concentrations of the LC50 values (6.69%, 3.34% and 2.23%) and control (0.00%) were used in a static/renewal bioassay. The differential growth in saggittal otolith and somatic parameters across exposure concentrations were examined by taking somatic and otolith morphometric measurements. Effluent samples and exposure concentrations were analyzed for some physico-chemical parameters while effluent samples were also analyzed for cyanide and heavy metals: Pb, Cu, Mn, Zn, Fe, Ni, Cd, As and Cr. The weight of the right otolith of lower exposure concentrations (0.00, 2.23, 3.34%) was significantly heavier (p<0.05) than those of the highest exposure concentration (6.69%). No other significant differences were observed across somatic and otolith parameters examined. Effluent sample was characterised by low DO, high TS, TDS and TSS while exposure concentrations and effluent sample had alkaline pH and BOD and COD values that exceeded the Federal Ministry of Environment (FMNEV) limits for effluents discharged into surface waters. The values of Cr and cyanide also exceeded FMNEV limits. These constituents may elicit adverse environmental and public health effects if continued and unregulated discharge of effluents is not restricted. The relative sensitivity of otolith parameters over somatic parameters, and the relative sensitivity between otolith parameters were demonstrated. The suitability of otolith weight as a probable early-detector of stress in natural environments is suggested.
Keywords: otolith, somatic indices, textile factory effluent, Clarias gariepinus.