Food spectrum of two co-occurring invasive fish, Cyprinus carpio Linnaeus, 1758 and Clarias gariepinus (Burchell, 1822) in Mattupetty Reservoir, Kerala, India.
The survey on fish fauna of the Mattupetty Reservoir in the Idukki District of Kerala State, India revealed the presence of four non-native fish species viz., Clarias gariepinus (family Clariidae), Cyprinus carpio (family Cyprinidae), Poecilia reticulata and Gambusia affinis (family Poeciliidae). Gut content analyses of Clarias gariepinus and Cyprinus carpio demonstrated no significant dietary overlap among them, though both are omnivorous. Cannibalism was observed in C. gariepinus and it was also found to feed on C. carpio and the latter feeds on the eggs of the former. Both the invasive fishes showed ontogenetic shift in diet. The initially invaded C. carpio might have facilitated the establishment of C. gariepinus, with the probable displacement of native species and currently these two invasive species are the only commercially valuable species available in the Mattupetty Reservoir. It is hypothesised that in a resource-scarce ecosystem like a reservoir with multiple invasive species, the invasive species not only feed on the indigenous food items available, but also feed on each other to ensure survival.