Distribution of tilapia, Oreochromis mossambicus (Perciformes: Cichlidae), and water body characteristics in Quintana Roo, Mexico

Based on field collection in freshwater bodies (1992 to 1996) in the Mexican State of Quintana Roo, Yucatan Peninsula as well as on official reports from the former Mexican Ministry of Fisheries, this work documents the distribution of tilapia in the state, and its relative abundance as a Function of water body area. Introductions of tilapia in Quintana Roo began in 1974; these were mainly extensive cultures (direct releases) until 1982, when floating cages began to be used. The fish were collected with throw, seine, and hand nets, plastic bags or hook and line, as the local conditions allowed; each fishing gear provided a separate abundance estimate for a given site. Water body area was calculated from maps (1:50 000) by clipping the lake area in homogeneously thick paper and weighing it to the nearest 0.1 mg. Temperature, conductivity and dissolved oxygen, as well as the number of native fish species, were recorded, but these variables showed no relationship to tilapia abundance or distribution; however, tilapia was not found in the wild at water conductivities above 5500 mmho/cm. Escape from floating cages, perhaps caused by crocodiles or water level elevations, was found in 50% of the intensive culture sites visited. Moreover, tilapia (Oreochromis mossambicus and hybrids, probably with O. ni[oticus) was captured in four sites where it had not been officially introduced; two of these may be natural invasions from nearby lakes during wetter cycles, the others (lakes Coba and Makanxoc) probably are unofficial introductions. Tilapia was not frequent throughout Quintana Roo (4.2% of 237 water bodies visited), but it was dominant (>20% of the total number of individuals) in most localities where it appeared, including lake Chichancanab, habitat of an endemic Cyprinodon species flock. The correlation between the logarithm of water body area and tilapia relative abundance significantly negative, possibly meaning that smaller sites were more vulnerable to tilapia was proliferation.