AbstractsBiology & Animal Science

Tese de mestrado. Biologia (Ecologia Marinha). Universidade de Lisboa, Faculdade de Ciências, 2015 The objective of this study was to assess the variability in condition for juvenile common two-banded sea bream Diplodus vulgaris in nursery areas of the main Portuguese estuaries using several individual condition indices. Estuaries and coastal lagoons play an important role for juveniles of marine fish because they offer areas with high availability of food, high water temperature and lower predation. These characteristics permit a fast and safe growth of fish until they reach adequate size to return to the ocean and to join adult populations. In this study, two indices estimated by analysis of otolith microstructure were used: widths of the 10 last and of the 60 first daily increments were considered as recent growth index and initial growth index, respectively. Furthermore, two common condition indices were also used: biochemical RNA:DNA ratio, that assesses nutritional status of individuals, and morphometric Fulton's K, that gives an estimate of general well-being of individuals. Since recent growth index and RNA:DNA ratio were significantly related with total length of individuals, a correction was performed and corrected condition indices recent growth’ index and RNA:DNA’ ratio were considered. Fulton's K was also significantly related with total length of juveniles and for this reason was replaced by condition factor K', which considers allometry in the growth of fish. Condition factor K' was considered in the study. A significant positive correlation between recent growth’ and initial growth indices was obtained. Results of the multiple regression analyses seem to reflect the discrepancy in the response times of the different condition indices used. In general, Sado, Ria Formosa and Guadiana provided juveniles in better individual condition. Future studies should be done to better investigate relationships between condition indices and between condition indices and environmental variables, focusing on the link between individual condition and habitat quality of nursery areas. O objetivo deste estudo foi avaliar a condição dos juvenis de sargo-safia, Diplodus vulgaris, em áreas de viveiro dos principais estuários da costa Portuguesa, utilizando vários índices de condição individual. Os estuários e lagoas costeiras desempenham uma função importante para os juvenis de muitas espécies de peixes marinhos porque oferecem elevada disponibilidade de alimento, águas quentes e menor pressão predatória. Estas caraterísticas permitem que os juvenis cresçam rapidamente e em segurança até atingirem dimensões suficientes para regressar ao mar e recrutar para as populações adultas. Neste estudo, foram usados dois índices baseados na análise da microestrutura dos otólitos: as larguras dos 10 últimos e dos 60 primeiros incrementos diários foram considerados como um índice de crescimento recente e um índice de crescimento inicial, respetivamente. Além disso, foram considerados o rácio bioquímico ARN:ADN, que estima o estado…