Efeito dos ambientes estuário e reservatório na fecundidade de Macrobrachium amazonicum (Decapoda: Palaemonidae) (Heller, 1862)

Abstract

Studies reveal that the Amazon region is suffering a strong anthropogenic and climatic influence which interferes in the environmental conditions. In crustaceans, climate change can influence growth and reproduction, and as life history patterns is influenced by environmental factors, the fertility is an important factor to estimate the reproductive potential and natural population stock. The specie Macrobrachium amazonicum has a wide geographical distribution and ecological and morphological plasticity. Based on the hypothesis that the physical and chemical conditions different of the environment influence on populations of M. amazonicum, we have the following question: What are the main environmental factors that will influence M. Amazonicum fecundity between populations of different places? Thus, the aim of present study is to determine the influence of physical and chemical factors on the relative fecundity of populations of M. amazonicum in estuary and reservoir. In the period of study, temperature, pH, salinity, turbidity and dissolved oxygen concentration in the water were obtained in situ. Precipitation was obtained from INMET, 2018 with establishment of four seasonal periods: dry, transitional dry-rainy, rainy, transitional rainy-dry. A total of 255ovigerous females, 181 from the estuary environment and 75 from the reservoir were collected for analysis of biometrics, number and size of eggs throughout the year. Embryonated eggs were measured according to the developmental stages. In the relationship effect of the environmental variables on the ovigerous females, turbidity and precipitation were the main factor on estuary. The mass-length relationship of females was represented by the following equations, Mt = 0.017xCt2.630 (R² = 0.880) for the estuary and Mt = 0.021xCt2.441 (R² = 0.810) for the reservoir, where ovigerous females in the estuary were larger and larger mass in comparison to the reservoir. In the relationship between fecundity and biometry of the animal, from both sites, there was a high positive correlation, between the length (r = 0.788) and the weight (r = 0.843) of the ovigerous females, as well as the relation with the morphometry of the eggs. The estuarine environment presented females with the highest amount of eggs in the dry-rainy and rainy periods in relation to the females from the reservoir that presented the highest fecundity in the rainy-dry and dry season. In our results observed four stages of development considering the presence and the appearance of the eye, and the eggs of the females reservoir, although in smaller numbers, presented larger sizes in relation to the estuary. The correlation observed if the physical and chemical factors influence the fecundity of M. amazonicum from the estuary was confirmed, with precipitation and turbidity being the factors that contributed the best reproductive performance of the species in the estuary. When it comes to the reservoir, we believe that there is a combination of all the environmental factors involved promoting the tolerance of the animal to maintain its life cycle.