Reproductive period and growth rate of the freshwater snail Heleobia parchappii (d'orbigny, 1835) (Gastropoda: Rissooidea) in a shallow brackish habitat (Buenos Aires Province, Argentina)

CLAUDIO GERMAN DE FRANCESCO; ISLA, F.I.

Malacologia

Institute of Malacology

Lugar: Ann Arbor; Año: 2004 vol. 45 p. 443 - 450

0076-2997

Heleobia parchappii (d’Orbigny,1835) is a rissooidean snail very widespread in freshwater environments of Argentina,occurring at salinities <1 ‰. In 1998, we found a population of this species inhabiting a brackish canal (10 −34 ‰) located close to the headwaters of the Mar Chiquita coastal lagoon (37º31’07”S, 57 º18’30”W, Buenos Aires, Argentina). The aim of the present work is to analyse the reproductive period and growth rate of this species in this saline condition. Monthly collections were made from August 1998 to August 1999. Two hundred snails per sample were measured and size-frequency distributions (SFD) constructed. Data on reproductive periods, growth rates and shell sizes were estimated from comparisons of SFD diagrams along the year. Our results show that H.parchappii is able to develop permanent populations in brackish waters. The species exhibits a seasonal cycle of reproductive activity from spring to fall, with two main spawning peaks. Maximum growth rate takes place in fall, whereas it is lower during the rest of the year, and snails attain smaller sizes than in freshwater environments. These results may explain the great abundance of autochthonous concentrations of H. parchappii in past estuarine habitats from the same region.