Although several postulations concerning the change in the monthly pattern of larval abundance are possible, the following hypothesis was examined: because the spawning season of large female shrimps around May has come to be delayed since the early 1990s, there is low larval abundance before July. To test the hypothesis, the reproductive
traits of O. oratoria with regard to monthly pattern in the gonadosomatic index (GSI) and in the histological development of the ovary for each size class, size at first maturity and fecundity were investigated