Reprodução de peixes de riachos: uma abordagem comparativa entre as estratégias r e K

Abstract

The present study aimed to characterize reproductive strategy, focusing on energy investment, of two fish species present in the river Ubatiba (22º50 , 22º55 S e 42º43 , 42º50 W), Maricá, Rio de Janeiro: Parotocinclus maculicauda (K-strategist) and Astyanax hastatus (r-strategist). Were collected bimonthly from June 2010 to April 2011, in two sites, totaling 236 specimens for A. hastatus and 234 specimens for P. maculicauda. For each sample were recorded standard length (Ls, cm), total weight (Wt, g), gonad weight (Wg, g), sexes and maturity stage. Through the size structure, we observed that females reach a greater length, compared to males of both species. The relation weight / length for both species showed a negative allometric growth (below 3). For sex ratio, the χ2 test was applied and indicated that, for both species, there are significantly more females. The distribution sexes in the year showed that females remain in the majority throughout the year for P. maculicauda, with the exception of November / December for the A. hastatus, when the number of males becomes greater. The size at first maturity indicated values in the same length class (2.5 to 3.0 cm). The temporal variation in the frequency of non-reproductive and reproductive individuals along with the temporal distribution of individual values of GSI showed that Parotocinclus is reproduced with greater intensity in the rainy seasons (September to April), reducing their reproductive activity significantly in the dry seasons (May to August). Astyanax showed regular reproductive activity throughout the year with a small peak in November / December. Spawning of total type was found for Astyanax, while for Parotocinclus, spawning is split into three lots. In both species was observed an inverse relationship between volume and number of oocytes produced, with Astyanax producing many oocytes (fecundity: 463 + 213 oocytes / g fish) and reduced volume (diameter = 800 μm e volume = 0.26 mm3) and Parotocinclus producing a much lower number (fecundity: 47 + 13 oocytes / gram of fish) but with volume so much higher in vitellogenic oocytes (diameter = 1.600 μm e volume = 2.14 mm3). Thus the relative energy value was also much higher, with Astyanax producing vitellogenic oocytes with 0.4+ 0.08 cal / unit and Parotocinclus producing the same oocytes with 1.8+ 1.1 cal / unit. For the total investment in the production of oocytes to be spawned, was considered the type of spawning of each species, Astyanax spending 50.5 + 24 calories/gram/gram of fish and Parotocinclus spending 88.4 + 72.46 cal/gram/gram of fish. The Mann-Whitney test was used and showed no significant differences in energy investment (Mann-Whitney; U =235.0, p=0.08), indicating therefore that regardless of the strategy (r or K), energy expenditure in the production of oocytes is the same.