Biologia reprodutiva de Nassarius vibex (SAY, 1822) (MOLLUSCA: GASTROPODA: NASSARIIDAE) nos estuários dos Rios Ceará e Pacoti, Nordeste, Brasil

Abstract

Nassarius vibex is a common gastropod present in abundance in the Northeast estuaries. The reproductive biology of this species was studied to characterize it and verify the influence of environmental variables, occurrence of imposex and parasitism in two populations of the species, one in the Ceará River estuary and the other in the Pacoti River estuary, Northeast, Brazil. Rainfall and salinity seem to influence the reproductive characteristics of N. vibex, while temperature has no significant effect due to its low annual variation. The species has a female biased population, with monthly variations, but with no predominance of males in any of the months. The outer lip of the shell was used as an indicator of the species reproductive status, suggesting that this characteristic may reflect the maturity state of the animals. The germ cells of males and females were characterized. The populations examined were parasitized by digenetic trematodes, Cestoda and other unidentified parasites. Histopathological analysis were performed. Trematodes showed more deleterious effects on reproduction than the other groups, and their presence was numerically larger. In the Ceará River estuary there was greater diversity of parasites with reduced prevalence. In the Pacoti River estuary the diversity of parasites was lower, but the monthly rates were higher. Imposex was exclusively detected in the Ceará River estuary population. In this population was reported the occurrence of penis and vas deferens in the affected females, convolutions in the oviduct and changes in the glandular mass (capsule and albumen glands). This last change resulted in sterility in the affected females, probably due to the presence of abortive capsules. The following indices for imposex quantification were applied: % I, MPL, FPL, RPLI, VDSI and AOS. The species embryonic and larval development was determined. The spawning and development stages were recorded. The spawning period occurred between June and December. Nassarius vibex deposit ovigerous capsules on hard substrates and larvae hatches at the veliger stage. The occurrence of incubated capsules in the females vestibule was recorded for both estuaries and its relationship with environmental variables and parasitism was analyzed. Even showing similarities between the two populations, the establishment of clearly defined standards for the species was not achieved.