Life cycle and structure of a population of colomesus psittacus (bloch & schneider, 1801) (osteichthyes, tetraodontiformes), in the mangrove area of São Luis Island, Maranhão, Brazil

The striped puffer fish, Colomesus psittacus, belongs to the Tetraodontidae family, being one of the most frequent species in Maranhão estuaries. The main objective of this study was to present results about the structure of a population and the life cycle of C. psittacus present in an estuary under the influence of a mangrove swamp in the municipality of Raposa, São Luís island, Maranhão, Brazil. Sampling was monthly during the period of August 1999 and November 2000. A total of 374 fish specimens were collected, 114 males, 119 females and 141 with undetermined sex. The length range varied between 74-276 mm with a mean of 141.51 mm and standard deviation of 38.01. The sex ratio was tested by the Chi-square method, with a degree of freedom and a 0.05 degree of significance (χ2< 3,840), and the Chi-square obtained was 0.10, so there was no significant difference at the level of significance 5%, therefore, the hypothesis of equality between the sexes (1:1) was accepted. The average length at first maturation (L50) obtained for C. psittacus was 160.79 mm and the L100 was 197.71 mm for grouped sexes. C. psittacus completes its life cycle in the mangrove, as individuals in all stages of gonadal maturity were observed.