When low genetic variability in feral and hatchery-reared tilapia becomes a vicious circle: Oreochromis niloticus from Oaxaca, Mexico

Abstract

Several tilapia species in Mexican reservoirs have been used as food source for more than 40 years but little effort has been devoted to the conservation and genetic selection of those species. Our objective was to evaluate genetic variability in feral (n = 59) and hatchery-produced (n = 58) Oreochromis niloticus stocked in the Benito Juarez dam. Allozyme analyses for 13 enzymatic systems and general proteins yielded 27 genetic loci. Seventeen loci were polymorphic in at least one sample. The observed heterozygosity was lower than expected and the imbalance in the Hardy–Weinberg equilibrium in almost all loci was caused by heterozygote deficiency. The inbreeding coefficient was 84%. Although the evidence suggests moderate genetic differentiation, it is probable that a great proportion of the source of hatchery organisms is from feral organisms. According to our results, management of the hatchery strain is inadequate, therefore other breeding strategies are needed to increase the genetic variability of O. niloticus from Oaxaca.