Abstract
Captive reproduction is one of the problems faced in aquaculture requiring the manipulation of environmental factors and/or hormonal treatment. Thus, we seek to verify experimentally which gonadal changes were present in mature individuals of Astyanax altiparanae arising from decreased water level. Collections were made every four hours, initiated four hours before and finished 28 hours after stimulation, at the Fish Farming Station of Companhia Energética de São Paulo, São Paulo, Brazil. The gonads were analyzed by light microscopy. The females had ovaries in the spawning capable phase until 12h; in 16h, in a more advanced stage of spawning capable phase; and, from 20h, in the regressing phase. Males had testes in the spawning capable phase until 8h; in 12h, in a more advanced stage of spawning capable phase; and, from 16h, the return to the spawning capable phase. The morphological description was corroborated by the proportion of cell classes. Females presented variation on the gonadosomatic index, but it was not found an emptying of the gonad for neither sex. The process of inducing reproduction with water level drawdown was considered satisfactory, since both sexes presented a reduction in the number of mature gametes at the end of the sample period.
Highlights
The seasonal reproduction in fish occurs due to the interaction of physiological functions with environmental cycles (Bollough, 1939; Sundararaj & Vasal, 1976; Sundararaj et al, 1980)
The water level drawdown applied to specimens in spawning capable phase of Astyanax altiparanae to induce reproduction was effective
The reducing of the water level can be considered a stressor and it is known that stress, most often, triggers a negative response in the reproductive success for both males and females (Consten et al, 2001; Mosconi et al, 2006; Cleary et al, 2007)
Summary
The seasonal reproduction in fish occurs due to the interaction of physiological functions with environmental cycles (Bollough, 1939; Sundararaj & Vasal, 1976; Sundararaj et al, 1980). Environmental factors act such as flags of a favorable station to reproduction, which are perceived by external receptors, and affect the central nervous system, pituitary, and gonads (Rocha & Rocha, 2006). In latitudes where the seasonal temperature fluctuations are small, flooding seems to be the main trigger for the reproduction of many fish species (Agostinho et al, 2004). The floods have an essential role in spawning stage (Godoy, 1975), while the first rains after the dry season are considered stimuli for the formation and movement of migratory fish shoal (Agostinho et al, 2003)
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