Population structure and relative growth of freshwater prawn Macrobrachium brasiliense (Decapoda, Palaemonidae) from São Paulo State, Brazil.
MANTELATTO1, F.L.M. & BARBOSA1, L.R.
1 Laboratório de Bioecologia e Sistemática de Crustáceos, Departamento de Biologia, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto (FFCLRP). Universidade de São Paulo (USP), Av. Bandeirantes-3900, CEP 14040-901, Ribeirão Preto (SP), Brasil.
ABSTRACT: We conducted a study of M. brasiliense to examine the population biology with emphasis on sex ratio and size frequency distribution and to describe the mathematical equations referring to relative growth used to detect sexual dimorphism. The specimens were analyzed in terms of population structure, male:female ratio, size frequency distribution, recruitment and relative growth. A total of 280 animals were monthly collected during one year. Proportion of females (72.14%) was significantly higher than that of males (27.86%) and ovigerous females were absent. There was no correlation between the variation of temperature or rainfall and number of males and females captured. Sex dimorphism was observed with respect to size, with males being significantly heavier and larger than females. Seasonal variation in female size associated with the peak of juvenile recruitment from March to June support the hypothesis of a greater reproductive activity in summer, despite no collected ovigerous females during this season. According to the sexual proportion of individuals in size classes, the reversal pattern was observed for the population studied. The relative growth allow us to infer that sexual maturity is reached between 9 and 10 mm of carapace length for both sexes, a size when the difference in growth is observed for males and females. Macrobrachium brasiliense is a species without economic importance but shows atypical biological patterns that encourage further studies on reproduction and population dynamics.
Key-words: Crustacea, Palaemonidae, freshwater prawn, growth.