Reproductive period, fecundity and histology of gonads of two cheirodontines (Ostariophysi: Characidae) with different reproductive strategies - insemination and external fertilization

Abstract

The reproductive period and fecundity of the inseminating cheirodontine Compsura heterura and of the externally fertilizing cheirodontine Odontostilbe pequira, from tropical and subtropical regions of Brazil, respectively, are described. The reproductive period of C. heterura lasted from January to April 2002, while O. pequira showed two reproductive periods, the first during September and October 2001 (spring), and the second between January and February 2002 (summer). Smaller classes of SL of females of O. pequira predominated in the second reproductive period, suggesting individuals born in the first period become shortly sexually mature, participating in the second reproductive period. In C. heterura, from a tropical region, temperature showed significant correlations with the variation in the gonadosomatic index (GSI) for both sexes, and rainfall showed significant correlation with the variation in the GSI only for females. In O. pequira, from a subtropical region, photoperiod was the only factor that showed significant correlations with the GSI variation in both sexes. The mean relative fecundity of C. heterura was 0.55 oocytes per milligram of total weight, similar to that of other cheirodontines with external fertilization, refuting the hypothesis, at least in Cheirodontinae, that insemination provides diminishing energy expenditure for the production of oocytes, due to a greater probability of fertilization. The mean relative fecundity of O. pequira was 0.8 oocytes per milligram of total weight, the largest known among cheirodontines. Spermatozoa were found inside the ovaries of maturating, mature and semi-spent females of C. heterura supporting the hypothesis of temporal separation between courtship and spawning. The largest relative weight of testis and the presence of sperm in maturing ovaries outside the reproductive period in C. heterura support the hypothesis that males of inseminating species make a greater investment in gonadal development than those externally fertilized.São descritos o período reprodutivo e a fecundidade do queirodontíneo inseminador Compsura heterura e do queirodontíneo de fecundação externa Odontostilbe pequira, coletados nas regiões tropical e subtropical do Brasil, respectivamente. O período reprodutivo de C. heterura estendeu-se de janeiro a abril de 2002, enquanto que O. pequira apresentou duas etapas reprodutivas, a primeira de setembro a outubro de 2001 (primavera), e a segunda de janeiro a fevereiro de 2002 (verão). Classes de comprimento padrão menores predominaram no segundo período reprodutivo, sugerindo que indivíduos nascidos no primeiro período tornaram-se sexualmente maduros rapidamente, participando do segundo período reprodutivo. Em C. heterura, de região tropical, a temperatura apresentou correlações significativas com as variações de índice gonadossomático (IGS) em machos e fêmeas, e a pluviosidade somente para fêmeas. Em O. pequira, de região subtropical, o fotoperíodo foi único fator que apresentou correlação significativa com as variações de IGS em ambos...

Reproductive ecology of Odontostilbe pequira (Steindachner, 1882) (Characidae, Cheirodontinae) in the Paraguay River, southern Pantanal, Brazil

“…Despite the mean length of O. pequira being similar to those found in other Cheirodontinae fishes in tropical regions of Brazil (Silvano et al 2003;Lourenço et al 2008b;Benitez and Súarez 2009), the median length of the females and males is similar to the minimal lengths found by Oliveira et al (2010) for O. pequira in southern Brazil (sub-tropical region). This observation can be explained by two hypothesis: 1) The samples of Oliveira et al (2010) has biased to higher individuals, in response to the use of 5 mm mesh size of the net, which influenced the sampling of smaller individuals or 2) The high temperatures during most of the year that lead to high productivity in the southern Pantanal, would result in rapid growth up to sexual maturity and consequent decrease in growth after the L 50 , leading to a greater representativeness in smallsized classes.…”

“…The absolute fecundity of O. pequira was low (181.4) in relation to the fecundity (795) found for the same species in southern Brazil (sub-tropical region) (Oliveira et al 2010), as for other Cheirodontinae fishes with external fertilization (Gelain et al 1999;Oliveira et al 2002;Silvano et al 2003), although such works report on seasonal reproductive periods. This behavior appears clear, because the fecundity of the inseminating Cheirodontinae Macropsobrycon uruguayanae was shown to have a similar value (191.08 oocytes) (Azevedo et al 2010), which could be a viable tactic among the Cheirodontinae fishes, which have a long reproductive period, independent of the type of fertilization.…”

“…The long reproductive period was also found by various authors in small-sized species (Mazzoni et al 2002(Mazzoni et al , 2005Hojo et al 2004), but not corresponding with a reproductive strategy for seasonal environments (Munro 1990;Vazzoler and Menezes 1992), characterized by species with a short reproductive period associated with the favorable conditions of flooding (Tedesco et al 2008), as reported for Moenkhausia sanctaefilomenae in the northern Pantanal (Lourenço et al 2008a). Furthermore, the long reproductive period shows a intraspecific variation in O. pequira, once Oliveira et al (2010) in studying the reproductive period of the same species in southern Brazil (sub-tropical region) found two reproductive steps, from September to October and from January to February.…”

“…This observation can be explained by two hypothesis: 1) The samples of Oliveira et al (2010) has biased to higher individuals, in response to the use of 5 mm mesh size of the net, which influenced the sampling of smaller individuals or 2) The high temperatures during most of the year that lead to high productivity in the southern Pantanal, would result in rapid growth up to sexual maturity and consequent decrease in growth after the L 50 , leading to a greater representativeness in smallsized classes.…”

“…The larger body size reached by the females of O. pequira in relation to the males is a common characteristic for many fish species (Mazzoni et al 2005;Mazzoni and Silva 2006), including Cheirodontinae fishes (Gelain et al 1999;Oliveira et al 2002) such as O. pequira (Oliveira et al 2010). In the females, the advantage of attaining greater lengths is mainly related to the fact the fecundity increases with the size of the individual (Wootton 1992), and thus, the production of a larger number of oocytes should assure the survival of the species.…”