Aspectos etnobiológicos, biológicos e viabilidade para o cultivo de larvas e juvenis em laboratório de Cardisoma guanhumi Latreille, 1828

Abstract

The present study aims to supply data about the ethnobiological and bioecological aspects and feasibilities of the larvae and juvenile culture of the crab C. guanhumi. This work was separeted in six parts, executed from January 2002 to December 2004, using the crabs of Sepetiba Bay, RJ. The first study took place to verify the economic importance of the crab, through to the profiling of the social economic situations of the crab fisherman and the ethnobiological data of the mangrove community of Barra de Guaratiba. For this 50% of the communities were interviewed through questionnaires. It was confirmed that the activity had been increasing exponentially in the region, due to high unemployement this in turn had increased the availability and therefore made the sale of the crabs harder. The crab fisherman demonstrated knowledge about the crabs biology and respect for the protection laws but they admitted that they were not always law-abiding due to their financial difficulties. The second study was about embryonic development, where the 28 ovigerous females were collected, and were transported to the laboratory, the eggs were observed and photographed daily. It was determined a total of seven embryonic stages and that the average incubation time was 20,8 days. In the third study the larval hatching rhythm and fertility were studied. A total of 54 ovigerous females were collected and were observed until the larval hatching, which occurred during the night, on the full moon and at low tide which facilitated the dispersion process. The average fertility was 165.300 ± 36.754,22 larvae and the hatching rate of the eggs was around 90% of the eggs that arrived at the final embryonic development. The fourth part was to show knowledge about the larval migration process of the C. guanhumi. The samples were taken using a plankton net with mesh 250μm, which were drawn up by a small boat during a ten minute period at eight stations.It was verified that the species probably showed the dispersal mechanism in relationship to the water currents in Sepetiba Bay. In the fifth part four experiments took place, which tested the light, feeds and stocking density influence through the larval survival and post-embryonic development. In regards to these experiments it was concluded that for the larviculture of this species it is important the larvae be maintained in dark flasks, the food must be live algae and rotifer only in the first days of growth, but newly hatched Artemia sp. nauplii were necessary at the end of the first week and the introduction of the wet ration near the end of the second week. This food must be maintained until the end of the larval development. The larval stocking density must be above 150 larvae per liter, but it must not reach 400 larvae per liter as it stimulates the larvae competition and cannibalism. In the sixth part juvenile development was studied, where 70 animals were individually kept and fed on wet ration. The juveniles were observed from the first stage to the ninth stage, where they showed slow development in the laboratory,where the moulting period showed a normal pattern to the crustacean. It is proven that urgent methods for a feasible management and conservation of the natural stocks of these species are needed.