Abstract
The objective of this study was to analyze the gonadossomatic relation of males and females of Brycon opalinus (the Pirapitinga do Sul) in the Serra do Mar State Park--Núcleo Santa Virgínia. The study area included three rivers: Paraibuna, Ipiranga, and Grande. From the gonadossomatic relation, it was possible to determine the reproductive season and strategy of this species. The gonadossomatic relation was high throughout the year for both males and females. Sperm competition and dilution of the ejaculate in the spawning locations favored substantial development of the testicles. The sex ratio of Brycon opalinus was always in favor of females. The existence of sexual dimorphism in this species was confirmed from the larger size of the females.
Highlights
Teleost fishes show the greatest variation of gonadal structure compared to other vertebrate groups (Srivastava and Sinch, 1994).The gonadossomatic relation (GSR) expresses the percentage which the gonads represent of the total weight of an individual, and is an efficient indicator of the functional state of the gonads (Vazzoler, 1996)
The GSR provides a basis for determining the period of greatest reproductive intensity, evidencing the reproductive strategy of each species
Among fish with external fertilization, the number of spermatozoa may be very limited because of the rapid dilution of the sperm when it is liberated into the water, and because of this, the amount of sperm may be insufficient to fertilize all the oocytes deposited during mating (Levitan et al, 1995)
Summary
Teleost fishes show the greatest variation of gonadal structure compared to other vertebrate groups (Srivastava and Sinch, 1994).The gonadossomatic relation (GSR) expresses the percentage which the gonads represent of the total weight of an individual, and is an efficient indicator of the functional state of the gonads (Vazzoler, 1996). The GSR provides a basis for determining the period of greatest reproductive intensity, evidencing the reproductive strategy of each species. These strategies can vary within a species, and even within a sex, and may occur in most taxa (Gross, 1996). Alternative mating strategies are expected in the presence of strong sexual selection or when some males are excluded from mating (Gross, 1985; Vieites et al, 2004). Among fish with external fertilization, the number of spermatozoa may be very limited because of the rapid dilution of the sperm when it is liberated into the water, and because of this, the amount of sperm may be insufficient to fertilize all the oocytes deposited during mating (Levitan et al, 1995). The reproductive success of the males depends on their distance from the females, the presence or absence of a potential competitor, and on the current velocity (Levitan, 2005)
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