Evaluation of Response Patterns in Somatic and Otolith Features of Laboratory- Reared and Wild Clarias gariepinus Exposed to Industrial Effluent

This study was aimed at comparing the responses of somatic and otolith features in Clarias gariepinus under chronic exposure conditions to industrial effluents in the laboratory for 60 days and in the wild for 6 months. Fish were collected upstream and downstream bi-monthly from a river receiving composite mixtures of industrial effluent while laboratory-rearedC. gariepinus were exposed to the same effluent mixtures in 60 days static renewal/bioassay using concentrations of 6.11, 3.05 and 2.23%, respectively and control series. A total of 21 variables representing saggital otolith and somatic data from both wild and laboratory fish were subjected to factor analysis. For laboratory reared fish, PC 1 indexed as ‘otolith factor’, PC 2 indexed as ‘condition factor’ and PC 3 indexed as ‘paired fin factor’ accounted for 26.15, 19.01 and 12.55% of the total variance, respectively. For wild fish, otolith factor (PC 1) and condition factor (PC 2) accounted for 38.24 and 22.69% of the variance respectively. The first 3 components and the first 2 components for laboratory and wild fish accounted for more than 50% of total variance in data. Reliability index (Cronbach’s alpha (&alpha>0.70) showed that the ‘otolith factor’ had strong internal consistency and is reliable as a primary and viable index of stress for both laboratory and wild fish. The complementary role of condition factor in stress detection was also highlighted. The emergence of paired features (otolith, pectoral and pelvic fins) as sensitive parameters in toxicity responses may be an indication of the onset of asymmetry in these structures.