| Resumo: |
The Brazilian menhaden, Brevoortia aurea, is the only species of genus Brevoortia in South American Atlantic waters, being abundant in the Rio de la Plata estuary. The temporal and spatial reproductive pattern of this menhaden was analyzed in relation to the major hydrographic features of the region, and the reproductive biology was studied by using histological analysis of ovaries. B.aurea is a multiple spawner with indeterminate annual fecundity. Daily spawning activity was mostly in the afternoon (15:00 - 16:00),based on the incidence of females with both hydrated oocytes and postovulatory follicles. Spawning frequency, determined using the percentage of females with postovulatory follicles, was about 12. during November. At this frequency, each female on average spawned a new batch of eggs every 8 days. Our results also show that some spawning activity occurs during virtually every month of the year, but the main reproductive period extends from September (late winter) to January (early summer). B.aurea in the region spawns almost exclusively in the Rio de la Plata estuary. Here their eggs occur in a thermohaline range of 13-23°C and 10-25 psu, mainly in stratified waters. Spawning takes place in coincidence to the bottom salinity front, probably in a convergent flow between the riverine and estuarine waters that generate egg retention. Contrary to the northern menhadens, whose life cycles are characterized by drift of the early life history stages, egg retention seems to be a main feature of the life cycle. of the Brazilian menhaden. This reproductive pattern is also shared by Micropogonias furnieri (whitemouth croaker), which is the most abundant species in the area. Both species, B.aurea and M.furnieri, seem to besalt water spawners in Lagoa dos Patos (a large coastal lagoon in southern Brazil, 300 Km northward the Rio de la Plata estuary), showing strategic variations in their reproductive patterns in response to the different dynamic conditions of both estuaries.
Universidad Nacional de Mar del Plata, Facultad de Ciencias Exactas y Naturales
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