“Development of the secondary sexual characters in the australian freshwater crayfish, Cherax quadricarinatus (Parastacidae)”.

VAZQUEZ FJ, CHAULET A, RODRÍGUEZ EM, LÓPEZ G LS.

Santinho, Florianópolis, Brasil

Congreso; 3rd Brazilian Crustacean Congress and 2004 TCS Summer Meeting; 2004

Sociedad Brasilera de Crustáceos

Cherax quadricarinatus is a freshwater crayfish farmed in Australia and overseas. It is a gonocoric species, although a variable proportion of intersex animals are found. Both males and females have a greater somatic growth in a monosex culture than in a mixed culture, having isolated males a significant higher growth than females. Therefore, the early identification of sex could improve the growth rate of monosex cultures from juvenile stages, as well as to increase the probability of inducing the sexual reversion of both females and intersex juveniles to males. The aim of this work was to determine the earliest stage at which the secondary sexual characters can be recognized in C. quadricarinatus.  Recently independent juveniles (stage III), were isolated in plastic containers filled with 200 ml of dechlorinated freshwater, fed daily ad libitum on Elodea sp and Tetradiskus® granules and maintained at 25-27 ºC and a photoperiod of 14: 10 light: darkness. Molted or dead individuals were daily recorded. Twice a month, juveniles were weighed and observed under stereoscopic microscope to determine the presence of the genital openings at the basis of the third (females), fifth (males) or both (intersex) pair of walking legs. The development of the genital openings began at body weights of 0,24 g for females and 0,24 to 0,28 g for males. Differentiation of the appendix masculino started within 0,30 to 0,60 g of body weight while the condition of intersex was observed from 0,30 g. In all cases, the differentiation of genital openings occurred at the juvenile stages VI to VIII, this is, approximately two to three months after the release of juveniles from their mothers.