This paper presents the results of observations carried on during the period 1964-1967 on fish captured by a fixed fish-trap, located in the Lagoon of Cananéia, São Paulo, Brazil. The local catch consisted mainly on two species: "carapeba" (Diapterus rhombeus) and "taínha" (Mugil cephalus) . Nine out of the 32 species captured in 1967 were studied in detail. Specimens of sexually matured "taínha" were present in a well defined period, from April to August, so that one may assume the possibility of spawning at that time. This period agrees with the minimum water temperature and local commercial fishing trap operations. The size of first sexual maturation was observed in six different species, respectively for male and female, "carapeba", 13 and 12 cm; "taínha", 33 and 38 cm; "parati" (Mugil curema), 28 and 30 em; "paru" (Pomocanthus arcuatus) , 11 and 13 em; "robalo" (Centropomus paralellus) , 24 and 16 em; and 18 em for female of "sargo-de-dentes" (Archosargus aries). This kind of fishing was influenced by meteorological and hydrographic conditions, mainly by water temperature and salinity.