No abstract

No abstract

The reproduction strategy of the Palaemonid shrimp, Macrobrachium arrtazorticum, has been studied on Careiro Island in a floodplain lake in Central Amazonia. Ovigerous females have been observed all year round. However, three periods of the hydrological cycle were significantly more favourable to gonad ripening: the middle of the rising and of the falling of the water level, as well as the low level. This suggests the direct effect of two factors: the current velocity and the phytoplancton production. At the population level, the maximum reproduction intensity has been observed during low water, and during rising water. This strategy increases the survival of planctonic larvae during the highest phytoplancton production period, and reduces the intraspecific competition, increasing the larval dispersal in the floodplain. In the lake, the percentage of ovigerous females was always higher regardless of size class of the adult prawns and of season, than in the channels or in the river, suggesting that the lacustrine environment is the more favourable to M. amazonicum reproduction. In eastern Amazonia, M. amazonicum shows a typical reproduction pattern of littoral Palaemonids: mass spawning occurs during the falling water, increasing the larval dispersion towards the estuary. The reproduction flexibility of M. amazonicum explains its success in colonizing a variety of environments in a wide geographical range in South America.

A ecologia do camarão Palaemonetes carteri Gordon, 1935 (Decapoda: Palaemonidae) foi estudada através de coletas mensais, realizadas de janeiro 1989 até maio 1990, na região de Manaus. P. carteri vive na liteira submersa dos igarapés de terra firme em áreas baixas inundadas periodicamente pelas enchentes dos rios. A estratégia de reprodução e a dinâmica da razão sexual foram estudados na base dos 4,441 indivíduos coletados. P. carteri mostrou um dimorfismo sexual do comprimento, as fêmeas sendo maiores que os machos. O período de reprodução foi restrito a enchente e a cheia das águas. O número de ovos por fêmea variou entre 5 e 39, sem nenhuma correlação com o tamanho das fêmeas. A razão sexual mostrou uma predominância de fêmeas sem nenhuma variação sazonal significativa.

Specimens of the prawn Macrobrachium amazonicum (Heller, 1862), parasitized by the isopod Probopyrus bithynis Richardson, 1904, were collected in the Lower Tocantins, Para, up to 300 km from the ocean. All the infested prawns displayed external sexual characters of the immature female. Of the prawns 99.6% carried a single parasite couple in either the right or in the left branchial cavity. The infestation level in the female host population varied between 1.6% and 7.3% in Cameta and between 6.4 and 54.5% upstream in Acaripucu, affecting respectively 4% and 11 % of the total prawn population. The length of the female isopod was positively correlated with the length of its host. The mean sizes of infested and non-infested female prawns, and of female parasites, displayed the same seasonal pattern of variation, with higher values from March to August during the time of the host's migration and reproduction, and lower values during the rest of the year during the recruitment of the prawns. The relationship between infestation level and host life cycle suggests a stable interaction between M. amazonicum and P. bithynis populations.