RESUMO
Semipalmated sandpiper Calidris pusilla arrives on the coasts of Venezuela between the middle of August and early September, staying there until May when birds prepare for vernal migration. To investigate possible relationships between corticosterone levels and body mass changes during preparation for migration, we sampled birds during wintering (January) and vernal premigration (May) over 2 years. Body mass and fat increased significantly from wintering to vernal premigration in both years. Capture stress levels of corticosterone varied between 30 and 150 ng mL(-1), the highest being during wintering. These results strongly suggest that increase in body mass of C. pusilla during preparation for vernal migration in a tropical environment was promoted by a decreased corticosterone secretion response to stress.
Assuntos
Migração Animal/fisiologia , Charadriiformes/sangue , Corticosterona/sangue , Estações do Ano , Estresse Fisiológico/fisiologia , Clima Tropical , Áreas Alagadas , Animais , Peso Corporal , Oceanos e Mares , Restrição Física , VenezuelaRESUMO
Oxydoras sifontesi and Pimelodus blochii are seasonal breeder fish. Spawn occurs once a year over a short interval of time, at the beginning of the rainy season. The gonadosomatic index (GSI), and plasma levels of steroid hormones of P. blochii and O. sifontesi were studied from fish samples, collected from the Portuguesa River (Portuguesa State, Venezuela) in 1998 and 2004-2005, respectively. Gonadal tissue samples were obtained and processed for histology. A macroscopic classification of the degree of gonadal maturation was performed using a six-stage maturity scale. Data was analyzed and compared as a function of the gonadal maturation stage. The GSI of both O. sifontesi and P. blochii increases from stages II to V (preparatory and prespawning periods) and decreases in the stage VI (postspawning). In males, the GSI was usually lower than in females. In both species, the higher plasmatic concentration of 17beta-estradiol (17beta-E) and testosterone (T) were obtained from specimens in stages IV or V. A significant decrease in both hormones was observed in stage VI, except for the males of P. blochii where T concentration did not change between gonadal stages IV-VI. The relevance of these results is discussed in relation to the seasonality and the particular hydrological conditions of the region.