Abstract
The gonadal development of the characin Astyanax aff. bimaculatus from Funil Reservoir, an impoundment in the middle reaches of the Paraiba do Sul River in southeastern Brazil was analysed through histological, histochemical and histometric techniques, and the spawning season was determined. Unbalanced sex ratio was found, with females outnumbering and reaching larger sizes than males. The following stages of oogenic cell development were identified for females: primary growth, pre-vitellogenic (cortical alveolar) and vitellogenic. In males, the following stages were determined: spermatogonia primary and secondary, spermatocyte primary and secondary, spermatid and spermatozoa. The spawning occurs most of the year, peaking in January-February, as indicated by the gonadosomatic index. In the peak of the spawning period, the condition factor and hepatosomatic indices decreased suggesting use of stored body energy reserves during the reproduction. Spawning in batches, small-sized oocytes and a long reproductive season suggest that Astyanax aff. bimaculatus fits to an opportunist strategy. Such strategy may facilitate the use of a wide range of lentic and lotic body waters in the Neotropical region.
Highlights
The life cycle patterns of fish are the most varied among the vertebrates and different reproductive strategies have enabled them to obtain success in different environments (Stearns 1992, Winemiller and Rose 1992, Blanck et al 2007, Belova 2008)
The reproductive strategies used by different fish species vary markedly (Dala-Corte and Azevedo 2010, Lowerre-Barbieri et al 2011) and the success achieved in different environments can have ecological and evolutionary implications (Rizzo et al 2002, Jamieson 2009)
Significant differences were found for the pooled fish (χ2(4, 90) = 29.38; p < 0.01) (Table 1)
Summary
The life cycle patterns of fish are the most varied among the vertebrates and different reproductive strategies have enabled them to obtain success in different environments (Stearns 1992, Winemiller and Rose 1992, Blanck et al 2007, Belova 2008). Differentiation, development and the release of sperm/oocytes throughout each reproductive cycle result in gonadal alterations that characterize different reproductive phases. Variations in the gonadal fish morphology reflect important ecological and behavioural adaptations during reproduction (Coward et al 2002, Fishelson and Gon 2008, Martins et al 2012). The histological stages of oocyte and spermatogenesis development together with macroscopic aspects of the gonads are used to characterize reproductive phases (Brown-Peterson et al 2011)
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