Percorrer por autor "Pina, T."
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- Comparison of RNA/DNA ratios obtained with two methods for nucleic acid quantification in gobiid larvaePublication . Esteves, E.; Chicharo, Alexandra; Pina, T.; Coelho, M. L.; Andrade, José PedroIn this paper, RNA and DNA contents and RNA/DNA ratios obtained with two fluorometric methods for the extraction and quantification of nucleic acids in individual estuarine gobiid larvae are compared. A total of 141 gobiid larvae, collected in the Mira and Guadiana estuaries (Portugal), were analysed. This study indicated that the nucleic acids content and RNA/DNA ratios of individual larvae varied with the procedure used. The two methods yielded similar log DNA values but different log RNA and log (RNA/DNA). The differences could be due to a number of factors related to specific steps of tested protocols. Comparison of nucleic acids contents and calibration of the two methods by regression analysis provided a reasonable basis for comparison although differences between estimates were evident.
- Gross and histological observations of ovarian development in twaite shad, Alosa fallax fallax, from Rivers Mira and Guadiana (Portugal)Publication . Esteves, E.; Pina, T.; Andrade, José PedroIn order to describe the stages of oogenesis of twaite shad, Alosa fallax fallax, 265 females were collected between March and June 1997, February and June 1998 and January and April 1999 in the Rivers Mira and Guadiana. From the histological study of ovaries a total of eight developmental stages were delineated. Gross examination of paired ovary revealed that they could be placed into one of seven maturity stages according to their stage of development. Two stages of atresia, alfa and beta,were identified. Upon cessation of spawning, the ovaries still contained some oocytes at various stages of development but with a greater number of atretic oocytes. The simultaneous occurrence of tes at different stages of development in the ovary indicates asynchronous oocyte development. Oocyte size frequency distributions do not show a gap in size between cortical alveoli and vitellogenic oocytes during the spawning season. This may represent the ability of twaite shad to push oocytes through vitellogenesis from a previtellogenic condition during the spawning period. This has important implications for twaite shad fecundity, because fish with this type of oocyte development depend on timates of batch fecundity and spawning frequency to determine potential annual fecundity.
- The distribution of estuarine fish larvae: nutritional condition and co-occurrence with predators and preyPublication . Esteves, E.; Pina, T.; Teodosio, Maria; Andrade, José PedroFish larvae were collected monthly between March and September 1997 in the Mira and Guadiana estuaries (southern Portugal). Hydrological parameters were registered and zooplankton samples were obtained simultaneously. Densities of fish larvae (ind·100 m–3) were calculated from 211 samples and larval nutritional condition measured as RNA/DNA ratios were obtained for 346 individuals, using a fluorimetric method for nucleic acid quantification. Correlating variables were further studied using multiple regression analysis in order to assess the relative importance of abiotic and biotic factors affecting within-year trends in abundance and nutritional condition of estuarine fish larvae. Results indicated that: 1) the abundance of fish larvae seems conditioned by temperature and predation; and 2) their nutritional condition is dependent on temperature and prey availability. Temperature is an important variable structuring estuaries and therefore conditions the behaviour and physiology of fish larvae. Furthermore, the co-occurrence of predators and larvae might be related to similar feeding patterns or comensalism. Whenever feeding conditions are suitable, they usually determine enhanced growth and nutritional condition. However, predation seems to control this latter relationship through its effect on larval mortality.