Morpho-meristics, maturity stages, gsi and gonadal hormone plasticity of African catfish Clarias gariepinus (Burchell 1822) that invaded into the Ganga River, India.
Background: African catfish Clarias gariepinus introduced to India has gravitated into the Ganga River as an invasive species. Morphological plasticity and reproductive adaptation are considered and reported as important manifestation contributing to evolution and persistence of an invasive species in the novel environment facilitating its expansion and establishment. African catfish in the Ganga River although documented to exist, it is yet to investigate if it elicits adaptation responses through morphological and reproductive plasticity in the riverine conditions. Therefore, morpho-meristic changes, plasticity in the reproductive stages, gonadosomatic index (GSI) and gonadal hormones were examined in C. gariepinus that invaded into the Ganga River so as to ascertain its invasion success. Results: Out of 23 morpho-meristic characters examined, head length (HL), head depth (HD), anal fin length (AFL) and the pectoral fin rays (PECFR) were observed to differ significantly (p < 0.05). The correlation coefficient 'r' between log length and log weight was found to be 0.9690 in culture and 0.8754 in river-caught specimens respectively. A distinct deviation in the maturity stages, GSI as well as gonadal hormones (testosterone, estradiol 17-β and vitellogenin) was further observed to change significantly in specimens of African catfish captured from the Ganga River as compared to those available in culture. Highest level of testosterone was found in males having gonadal stage V which was 184.82±10.4 pg/ml in culture and 204.82±21.34 pg/ml in river-captured specimens. The mean value of serum estradiol-17β was lowest (67.25±11.4 pg/ml) in gonadal maturity stage I and highest (328.73±24.5 pg/ml) in stage V in the river-captured C. gariepinus. The vitellogenin level in female C. gariepinus was detected in stage III, and it was maximum in stage V where it was 16.68±2.98 pg/ml in river-captured specimens and 12.63±2.12 pg/ml in cultured fish. Conclusion: The results of this study on morpho-meristic and gonadal plasticity provide first evidence of invasion success of the African catfish gravitated in the Ganga River which has now adapted to the river environments for breeding and establishing. The variations concerning different reproductive phases and the gonadal hormones in culture and river-caught C. gariepinus have been considered to contribute to the success of the colonisation and establishment. The knowledge generated on the phenotypic and reproductive plasticity of African catfish available in the Ganga River will help management and control programmes.