The temporal pattern of reproduction and recruitment is described from monthly population samples (June, 1989 through November, 1990) of two penaeid shrimp species, Trachypenaeus similis (Smith) and T. constrictus (Stimpson), from an inshore location (Mississippi Sound near Horn Island) in the Northcentral Gulf of Mexico. The presence or absence of mating plugs (associated with mating and insemination) and ovarian maturity (an indicator of spawning) were used to examine breeding in adult females. Females with mature ovaries occurred in samples from April through October and November in T. constrictus and T. similis, respectively, with peak values in July to September in both species. The percentage of inseminated females fell to low or zero values in the late fall and winter, indicating a cessation of mating activity. Sexual maturity of males was indicated by fusion of the gonopodal endopods (petasma); mature males were present throughout the year in both species. Recruitment intensity was described as the percentage of juvenile individuals in monthly population samples of each species (''identifiable juveniles''). Very small Trachypenaeus juveniles, at a size closer to actual recruitment but too small to be identified to species (''unidentifiable juveniles''), were used in calculating another recruitment index based on combined monthly samples of both species. Both indices indicated that recruitment occurred throughout most of the year with no obvious seasonal pattern. The monthly spawning intensity of each species was highly correlated with water temperature at the month of sampling, indicating the possible importance of temperature as a proximate factor acting on gonadogenesis and spawning pattern. It is hypothesized that larval food supply may be an important ultimate factor or selective pressure acting on spawning seasonality in these penaeid shrimps. There were no statistically significant correlations between monthly estimates of spawning intensity and recruitment using lag periods from one to 3 months, indicating a complex stock-recruitment relationship in these species.
