The Fish Population Size of Tepetitlan Reservoir (Mexico) is at a Critical State

Aims: To determine the fish population structure of the Tepetitlan reservoir in the state of Mexico, Mexico, identifying the present species, distribution, age, length and weight.

Study Design: Convenience sampling.

Place and Duration of Study: Tepetitlan reservoir in the state of Mexico, Mexico, from April to September 2011.

Methodology: Each month, at least 200 fish were used for morphological measurements (weight, total length, standard length, max height and perimeter) and reproductive traits such as sex and gonadal maturity stage. Descriptive statistics were used to characterize the population structure, age and size of first capture. Growth parameters, natural mortality, instantaneous fishing mortality rate, exploitation rate, yield per recruit potential growth model were all 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: The Tepetitlan reservoir has a small population of shortfin silverside (Chirostoma humboldtianum) with average catch sizes of 11 cm, and rare presence of axolotls (Ambystoma mexicanum) and marbled crayfish (Procambarus sp). The fishing effort of 0.53 and exploitation rate of 0.44 indicate that the reservoir is used within its tolerance limits. The compressed size of the populations, potential problems of inbreeding and reduced physical space for the species pushes the habitat to a fragile situation for their permanence.

Conclusion: Tepetitlan reservoir has a dramatically small population of shortfin silverside (Chirostoma humboldtianum), and an extremely small population of axolotls (Ambystoma mexicanum) and marbled crayfish (Procambarus sp).