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

Abstract

The aim of the present study was to evaluate the seasonal pattern of the gonadosomatic index (GSI), condition factor (K), and sex ratio in the catfish Auchenipterichthys longimanus (Siluriformes: Auchenipteridae) as an approach to identify its reproductive period. A total of 589 A. longimanus specimens (251 males and 338 females) were captured in the rivers of the Caxiuanã National Forest, in the Brazilian state of Pará, between July, 2008 and July, 2009. Among the male specimens, 171 were classified as adults and 80 as juveniles, while there were 249 adults and 89 juvenile females. Using a sinusoidal equation, analysis of the GSI revealed a reproductive asynchrony between the genders, with males attaining their highest GSI values in January, while females peaked in March. For males, the sinusoidal regression for GSI values was significant only when used the complete data set (P=0.001), wears no trend was identified for bimonthly means (P=0.136). For females, by contrast, significant values were obtained for both the complete data set (P=0.012) and bimonthly GSI means (P=0.026). For the condition factor, the sinusoidal equation returned significant seasonal variation in both raw data (P=0.02) and with mean values (P=0.00) for males, but only with raw data for females (P=0.04), which appears to reflect variation in the energy budget between genders. With regard to the sex ratio, more reproductive females were captured than males in January and March, 2009, which suggests a pattern of segregation related to the reproductive process. These parameters are fundamental to the assessment, protection, and management of natural fish stocks, as well as providing guidelines for the development of conservation strategies.O objetivo deste estudo foi avaliar alterações sazonais no índice gonadossomático (IGS%), fator de condição (K) e proporção sexual, a fim de determinar o período de atividade reprodutiva do bagre Auchenipterichthys longimanus (Siluriformes: Auchenipteridae), a partir da análise de exemplares coletados em igarapés da Floresta Nacional de Caxiuanã, estado do Pará, Brasil. Através de coletas bimestrais entre julho de 2008 e julho de 2009, foram capturados 589 exemplares de A. longimanus, sendo 251 machos e 338 fêmeas. Dentre os machos, 171 exemplares foram classificados como adultos e 80 foram jovens, e dentre as fêmeas, 249 eram adultas e 89 jovens. Por meio do estabelecimento de uma equação senoidal, a análise do IGS% evidenciou uma assincronia reprodutiva entre os sexos, pois os machos obtiveram maiores valores de IGS% em janeiro e as fêmeas apresentaram seu pico em março. Para os valores de IGS% de machos, a equação senoide mostrou-se significante somente para os valores brutos (P=0,001), sendo não identificada uma tendência com os valores médios do IGS% (P=0,136). Para as fêmeas, os valores de significância da equação senoide para o IGS% foram obtidos tanto para os dados brutos (P=0,012) quanto para os dados médios (P=0,026). Para o Fator de Condição, a equação senoide demonstrou variação nos valores brut...

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

“…In T. piresi, gonadal activity peaked mainly in the dry season, which is distinct from the data available for other auchenipterid species (Araujo et al, 1999;Silva and Viana, 2003;Freitas et al, 2011;Maia et al, 2013;Santos et al, 2013). A reproductive peak in the dry season may be related to a strategy for the selection of spawning sites.…”

“…In A. nuchalis, females matured at larger sizes than males, a pattern found in other auchenpterids (Freitas et al, 2011;Santos et al, 2013) as well as many other tropical fishes (Barbieri et al, 2004;Nunes et al, 2004;Gomiero et al, 2007;Rodrigues-Filho et al, 2011;Prudente et al, 2015). In this case, size differences between males and females at first maturity may be related to reproductive competition, with males investing in early maturation in order to be ready to reproduce as soon as possible, ensuring the perpetuation of their genes.…”

“…Some recent studies have focused on reproductive parameters in a small number of auchenipterid species (Freitas et al, 2011;Maia et al, 2013;Santos et al, 2013). The present study provides the first published data on the biology of Tocantinsia piresi.…”

“…A predominance of females has been observed in other auchenipterids (Araujo et al, 1999;Becker, 2001;Freitas et al, 2011;Maia et al, 2013) and may be the result of population-level strategies adopted for the optimisation of reproductive success, given that males can fertilise more than one female (Burgess, 1989).…”

“…The variation in the hydrological cycle also plays a significant role in the maturation of the gonads, spawning season, and the larval development of fish species (Goulding, 1980;Ruffino and Isaac, 1995;Zeug and Winemiller, 2008;Queiroz et al, 2010;Freitas et al, 2011;Maciel et al, 2011;Prudente et al, 2015). Spawning during the filling and flood season may contribute to reproductive success in many fish species (Godinho et al, 2010), due in particular to the increased availability of habitats that favour the survival of larvae and fry (Agostinho et al, 2004).…”