Opportunistic reproductive strategy of a non-native fish, the spotted metynnis Metynnis maculatus (Kner, 1858) (Characidae Serrasalminae) in a tropical reservoir in south-eastern Brazil

摘要

We investigated the reproductive strategy developed by the non-native sh Metynnis maculatus (Kner, 1858) to explain its success in establishing in a tropical reservoir in south-eastern Brazil. A total of 198 specimens were examined, 100 males (total length, TL 110–172 mm) and 98 females (TL 110–191 mm), collected using gill nets from September 2005 to August 2006. Sex ratio is balanced, although females signicantly outnumber males in size larger than 160 mm TL. Six stages of oogenesis and ve of spermatogenesis are described, based on staining aspect of the nucleus and cytoplasm structure with photonic microscopy. A protracted reproductive period from August to January was found with females producing several large clutches of small eggs. Oocyte mean diameter ranged from 19.6–48.3mm in previtellogenic ovarian stage to 83.4–149.4mm in vitellogenic ovarian stage whereas in spawning stage ovary, oocyte diameter varied from 300 to 500mm. In ripe stage, oocytes can reach diameter up to 2.00 mm. Batch fecundity ranged from 670 to 16,333 oocytes (mean fecundity 7056 oocytes) for females having TL ranging from 145 to 191 mm and total weight ranging from 75 to 176 g. A tendency for opportunistic strategy was detected as indicated by a long spawning period, high fecundity, small oocytes and small body size that have proved to be effective in the Lajes reservoir.