Can weight/length relationship predict size at first maturity? A case study with two species of Characidae

Abstract

A weight/length relationship was established for Astyanax jacuhiensis (Cope, 1894) (n = 370) and Cheirodon ibicuhiensis Eigenmann, 1915 (n = 701), from samples taken monthly in Fortaleza Lagoon, Cidreira, Rio Grande do Sul, from December 1991 through November 1992. Both species showed a polyphasic allometric growth pattern, each stanza described by an independent power equation controlled by a switch function. For C. ibicuhiensis, this change in the growth pattern occurred at 2.948 cm standard length (SL), close to published sizes for the attainment of female maturity. The change in the growth pattern of A. jacuhiensis (SL = 3.481 cm) was below the predicted size at first maturity, and merits further investigation. Although not conclusive, our data suggest that a complex growth pattern is frequent in nature, and perhaps is not usually identified because trends are obscured by natural variability. Despite the increased complexity resulting from the application of a more-complex equation, the identification of a change in the growth pattern could indicate important aspects of fish biology, including the attainment of sexual maturity.A relação peso/comprimento para Astyanax jacuhiensis (Cope, 1894) (n = 370) e Cheirodon ibicuhiensis Eigenmann, 1915 (n = 701) foi estimada a partir de amostras mensais efetuadas na lagoa Fortaleza, Cidreira, Rio Grande do Sul (dezembro de 1991 a novembro de 1992). As espécies analisadas apresentaram padrão de crescimento alométrico polifásico, sendo cada fase descrita por uma equação potência independente controlada por uma função interruptora. Para C. ibicuhiensis foi identificada uma modificação no padrão de crescimento com 2,948 cm de comprimento padrão (CP), valor próximo à dados publicados relativos ao início da maturação sexual. A alteração observada no padrão de crescimento de A. jacuhiensis (CP = 3,481 cm) encontra-se abaixo do tamanho previsto para a primeira maturação e sugere a necessidade de investigação adicional. Embora não conclusivos, nossos dados sugerem que padrões complexos de crescimento são frequentes na natureza e, talvez, não identificados porque tendências sutis acabam por ser obscurecidas pela variabilidade natural dos dados. Apesar do aumento de complexidade resultante da aplicação de uma equação complexa, a identificação de mudanças no padrão de crescimento pode apontar para aspectos relevantes da biologia de peixes, incluindo a maturação sexual.

Growth of the silverside Atherinella brasiliensis in a subtropical estuary with some insights concerning the weight-length relationship

“…Although this general methodology is an interesting tool to describe the growth pattern for each specific stanza, as in Bervian et al (2006), Fontoura et al (2010 and Oliveira et al (2011), it sets the potential trap of achieving a good statistical result with little biological meaning. But the benefit of this approach does not lie in the stanzas themselves, but in identifying the breakpoint between stanzas, that could indicate an interesting shift in the species' life-cycle.…”

Seasonal changes in the gonadossomatic index, allometric condition factor and sex ratio of an auchenipterid catfish from eastern Amazonia

“…In this respect, it would be advantageous for a male to have early gonadal maturation, in order to be apt when the first females are ready for copulation, thus increasing their chances of success during a given breeding season (Fontoura et al, 2010).…”

“…However, the condition factor can suffer from any change related to the growth cycle of fish, a pattern already identified for perciforms (Bervian et al, 2006) and characiforms (Fontoura et al, 2010). Therefore, it would be appropriate to analyze such quantitative indices considering different size classes, since the energy budget of an individual can changes during ontogeny (Swain & Foote, 1999).…”

Influence of the flood pulse on the reproduction of Tocantinsia piresi (Miranda Ribeiro) and Auchenipterus nuchalis (Spix & Agassiz) (Auchenipteridae) of the middle Xingu River, Brazil

“…The size at first maturity (L 50 ) of each species was estimated applying the method proposed by Fontoura et al (2010), which uses the Gonadosomatic Index (GSI) values. The GSI was obtained for each individual based on / *100 Vazzoler, 1996), where M G is the mass of the gonads and M T is the total mass of the individual.…”

“…The GSI was obtained for each individual based on / *100 Vazzoler, 1996), where M G is the mass of the gonads and M T is the total mass of the individual. According to Fontoura et al (2010), the GSI values were then converted into relative proportion of the maximum GSI value recorded. The method predicts that all individuals for which this proportion is equal or greater than a pre-established percentage were considered to be engaged in the reproductive process.…”