Biologia da reprodução do dourado Salminus franciscanus no Rio São Francisco, a jusante da barragem de Três Marias: estudo histológico, imuno-histoquímico e ultraestrutural

Abstract

Studies on the reproductive biology of a species in its natural environment provide support for development of fish farming with native species and essential parameters for the establishment of fish conservation programs. A total of 283 specimens of the dourado Salminus franciscanus were captured in upper São Francisco River, downstream from the Três Marias dam, Minas Gerais, southeastern Brazil, during a reproductive cycle from August 2009 to July 2010. The gonadal maturity stages and spawning type were determined by histological features of the gonads, germ cell development and variations of the gonadosomatic index (GSI). For analysis of the oocyte surface and fecundity, mature females were subjected to induced spawning by hypophysation. Females were significantly larger than males and there was a marked predominance of males in all samples. The length-weight relationship showed positive allometric growth for females (b = 3.23) and isometric growth for males (b = 3.04), reflecting the great investment of females in breeding. Fish at resting (stage 1) were common in all samples, maturation and spawning (stages 2 and 3) were predominant in October-November and December-January and post-spawning (stage 4) occurred from December-January extending until April-May. The GSI followed the morphological changes of gonadal maturation, with a peak (7.08 in females and 3.46 in males) in October-November. By scanning electron microscopy, spawned oocytes showed a funnel-shaped micropyle and a simple arrangement of pore-canals in the zona radiata, which is typical in non-adhesive eggs. Absolute fecundity (AF) ranged of 167,048 to 440,320 oocytes per female and, relative fecundity was 3,341 to 7,102 oocytes/cm (TL) and 129 to 175 oocytes/g (BW), with coefficient of liner regression R2 = 86.14. Immunohistochemical and TUNEL reactions suggested a relationship among IGF1, cell proliferation and apoptosis in the regulation of the spermatogenesis of S. franciscanus. In summary, the results of this study indicate that S. franciscanus reproduces in upper São Francisco River from October to January, exhibiting total spawning, non-adhesive eggs and high fecundity, reproductive parameters of nonguarding, egg-scattering pelagic spawners, a reproductive style considered ancestral in the evolution of fishes.