Biologie de Prochilodus nigricans (Teleostei : Prochilodontidae) dans le bassin du Mamoré (Amazonie bolivienne)

#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

Measurements on ground or sectioned otoliths : possibilities of bias

Back-calculation usually requires measurements of growth marks revealed on otoliths by specific preparations. The standardization of the grinding (or sectioning) plane is necessary, but difficult, especially along the antero-posterior axis. In order to show the importance of the grinding plane, tetracycline labelling of eel otoliths (#Anguilla anguilla L.$) has been used. This marking has a calcio-traumatic effect on otoliths, which can be revealed with staining techniques. Unless the grinding plane is incorrect, the tetracycline labelling and the staining of the ground surface are then superposed. (Résumé d'auteur

Estimation de l'âge individuel de Prochilodus nigricans (Teleostei, Prochilodae) dans le Béni (Bolivie) : protocole d'étude et application

L'estimation de l'âge de #Prochilodus nigricans Agassiz, 1829 est réalisée à partir de 840 poissons pêchés de 1983 à 1987 dans les principaux milieux du réseau hydrographique de la rivière Mamoré (Béni, Bolivie). Diverses préparations et observations de pièces calcifiées (écailles, otolithes, rayon épineux dorsal et os operculaire), ainsi que les comparaisons de plusieurs lectures, ont permis de choisir l'écaille et ses marques de croissance pour estimer l'âge. Les pertes d'écailles, entraînant la présence de très nombreuses écailles régénérées macrocentriques, paraissant dûes à l'abondance des poissons lépidophages du genre #Roeboides. Les marques principales de croissance sur les écailles microcentriques sont décrites, ainsi que les principales anomalies ayant engendré des difficultés de lectur

Sources of variation in growth of the European eel (Anguilla anguilla) estimated from otoliths

Back-calculation usually requires measurements of growth marks revealed on otoliths by specific preparations. The standardization of the grinding (or sectioning) plane is necessary, but difficult. In order to show the importance of the grinding plane, tetracycling labelling of eel otoliths (#Anguilla anguilla L.$) has been used. This marking has a calcio-traumatic effect on otoliths, which can be revealed with staining techniques. Unless the grinding plane is incorrect, the tetracycline labelling and the staining of the ground surface are then superposed. (Résumé d'auteur