| Popis: |
Prochilodus nigricans$ is abundant in the whole Amazonian basin. The biology of the population living in the mid-Mamoré river, close to Trinidad (Béni, Bolivia), was studied between 1981 and 1987. We investigated its reproduction, growth, lenght-weight relationship and condition indice, and estimated its abundance. #Prochilodus nigricans$ has a high fecundity and a short reproduction season (January to March). Spawning occurs at the end of the flood on the lagoons banks. Hatching date was fixed to the first of February. Lenght and age at sexual maturity are respectively 27 cm and 2 years. Chronological regulation of spawning seems to depend of a variable maturation controled by some genetical processes. Lenght reaches about 20 cm at end of first year, and 38 cm for females and 36 cm for males of at least-5 years age. Females grow faster than males and have a higher longevity. The sex-ratio rapidely decreases with size and females become dominant. Demographic structure is characterized by absence of 1+fish, implying a downstream migration of the youngs at the end of the first year followed by an upstream migration after one year spent in the large lagoons of Northern Béni. As for other #Prochilodus$ species with similar biology, it is necessary to define the population units in order to manage these abundant living resources. (Résumé d'auteur) |
