Population Structure of Oreochromis sp. at El Rodeo Dam, Morelos State, Mexico

Aims: To determine the population structure of Oreochromis sp. and the current fishing effort at the El Rodeo dam in the state of Morelos, Mexico.

Study Design: Convenience sampling.

Place and Duration of Study: El Rodeo dam, state of Morelos, Mexico, between April and September 2010.

Methodology: Each month, a sample of organisms was caught with the help of local fishermen, and morphometric measurements of a minimum of 200 organisms were done. Morphological measurements of each organism included weight, total length, standard length, height at the beginning of the dorsal fin and maximum perimeter, as well as reproductive traits such as sex and gonadal maturity phase. Descriptive statistics were calculated to characterize the population structure. Size of first capture and recruitment size, age, and growth parameters. Natural mortality, instantaneous fishing mortality rate, exploitation rate, yield per recruit potential growth model were calculated by empirical equations and formulas. Differences between height and weight by sex, were explored by one-way analysis of variance defining weight as a covariate.

Results: A total of 1,344 organisms were measured. There were 7.5 males per female. About 73% of organisms correspond to sizes between 15 and 17 cm in total length. Average catch size is smaller than those reported in the literature for this species, which may be due to the season and sampling area, problems of inbreeding, early reproduction and selectivity of fishing gear used. The current fishing effort of 1.2 and the exploitation level of 0.56 indicate that the reservoir is within adequate limits of exploitation. However, the small size of the fish organisms causes to be commercialized at a very low price.

Conclusion: The dam is dominated by Oreochromis sp. The current fishing effort of 1.2 and the exploitation level of 0.56 indicate that the reservoir is within adequate limits of exploitation.