Human activities such as industries, agriculture, aquaculture etc., always impact the ecosystem particularly ecological biodiversity. Riverine ecosystems in India have been suffering from heavy human intervention, which leads to declined fishery of native fish species. Exotic fish species introduction in aquaculture, inadvertently found in native aquatic ecosystem, threats to endemic fishes and native fish fauna. African catfish, Clarias gariepinus was introduced to India from Bangladesh which is cultured in northeastern states (West Bengal and Assam) and southern state (Andhra Pradesh), together with the Indian Major Carps. Serious loss to the carp in such mixed culture ponds led farmers to switch over to monoculture of african catfish. The present study was conducted in Kadamba tank (known as half-sea), Tamirabarani river basin, Thoothukudi, Tamilnadu for the period of 12 month (June 2015 to June 2016), to understand the impact of introduced exotic fish species on its ecological diversity.
Fish samples were collected by gill netting and cast netting. The collected specimen were fixed in 10% formalin for further studies. Present study recorded 61 fish species, categorized under 8 orders viz., Cypriniformes (34 species), Perciformes (9 species), Siluriformes (8 species), Cyprinodontiformes (5 species), Anguiliformes (2 species), Beloniformes (1 species), Clupiformes (1 species), and Synbranchiformes (1 species). Among 61 species, 5 were endemic to Western Ghats, 6 were threatened, 5 were vulnerable, 1 was endemic to the Tamiraparani riverine system and 6 were exotic. The exotic fish species recorded during the study were, Tilapia (Tilapia mossambica), common carp (Cyprinus carpio), grass carp (Ctenopharyngodon idella), Mosquito fish (Gambusia affinis), African catfish (Clarias gariepinus, and Armoured sucker catfish (Pterygoplichthys disjunctivus). A survey was conducted among the local fisher folk indicated decline in native fish species at some stations of the lake with increase in catches of the African catfish (Clarias gariepinus). This increase in catches of African catfish at several locations in the lake indicated negative impact on the native fish diversity.
This is the first report about Kadamba tank at Tamiraparanei river basin. Since, Clarias gariepinus has spread into natural water bodies, affecting native fish species by way of genetic impact, disease introduction, and catastrophic ecological impacts such as predation, competition and environmental modification. Scientific studies on the impact of this species on the native fish biodiversity in the Kadamba tank and Tamirabharani river system are very scarce. The present effort could initiate more studies in the future that could bring insights into the emerging issue and prompt needed precautionary measures by management of native biodiversity. Further analysis and clarification will be presented in the conference.