IMPACTS OF NON-NATIVE FISHES ON THE FISH COMMUNITY AND THE FISHERY OF THE CIENAGA GRANDE DE SANTA MARTA ESTUARY, NORTHERN COLOMBIA

Abstract

In tropical coastal ecosystems very little is known about the impacts of non-native fish species on the native ichthyofauna and to the author's knowledge, there are no published studies focusing on Caribbean estuaries. This study aims to determine the impacts of the non-native fish Oreochromis niloticus on the abundance, species composition, feeding habits and fishery of native fishes, as well as the impacts of the non-native fish Trichogaster pectoralis on the abundance of native ichthyofauna, in the Cienaga Grande de Santa Marta estuary, Northern Colombia. No clear evidence has been found that indicates a negative impact of O. niloticus and T. pectoralis on the abundance and species composition of the native ichthyofauna. Additionally competition for food between O. niloticus and the native fishes does not seem probable due to the high abundance of their shared preys and the generalist and mixed feeding strategies of most native fishes. In fact, the fishery of O. niloticus represented an alternative income during a period when the most valued native fishes were scarce. However, there are indications of a high probability of negative impacts to occur: the proliferation of the Nile tilapia modified the species composition of the native fish communities dominating during a period of low salinity, and a potential impact on native benthic fish and fish biodiversity of the estuary can not be ruled out. Oreochromis niloticus and T. pectoralis have biological features that facilitate their proliferation in new environments and food resources seem not to be a limitation. However, until now their long term establishment seems to have been restricted by drastic environmental fluctuations (e.g. salinity) in the estuary. The findings indicate that the establishment of alien fishes with opportunistic feeding habits in tropical estuaries with a high environmental variability is more influenced by abiotic factors than biotic interactions like competition. However, further research should be conducted to establish the role of other biotic interactions (e.g. predation, competition for space, facilitation) and human factors like overfishing on hindering naturalization of non-native fishes in this type of ecosystems.