Population structure and relative growth of freshwater

ABSTRACT: Population structure and relative growth of freshwater prawn Macrobrachium brasiliense (Decapoda, Palaemonidae) from São Paulo State, Brazil. We conducted a study of M. brasiliense to examine the populat ion biology with emphasis on sex rat io and size frequency distribution and to describe the mathematical equations referring to relative growth used to detec t sexua l d imorph ism. The spec imens were ana lyzed in te rms o f population structure, male:female ratio, size frequency distribution, recruitment and relat ive growth. A tota l of 280 animals were monthly col lected dur ing one year. Proportion of females (72.14%) was signif icantly 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 recrui tment f rom March to June support the hypothesis of a greater reproduct ive act iv i ty in summer, despi te no col lected ov igerous females dur ing th is season. According to the sexual proportion of individuals in size classes, the reversal patter