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.
Highlights
Material and MethodsCharacidae is the largest family of Neotropical fishes, showing a high diversity in reproductive strategies among its representatives
The Mann-Whitney test was used to determine if absolute fecundity and body size of the females of O. pequira collected in the first reproductive period differed from those of females collected in the second reproductive period
Based on the mean monthly GSI values (Fig. 4) and on the frequencies of the stages of gonadal maturation (Fig. 5), it was estimated that reproductive period of C. heterura in the rio Ceará-Mirim began in January extending up to April 2002, when higher values of the gonadosomatic index (GSI) were seen, in males as well as females (Fig. 4; Table 1)
Summary
Characidae is the largest family of Neotropical fishes, showing a high diversity in reproductive strategies among its representatives. The tribe Compsurini, in which Compsura heterura Eigenmann, 1915 belongs, includes all the inseminating species of Cheirodontinae (Malabarba, 1998), characterized by transfer of sperm from the testis of the mature males to the ovaries of females, as described by Burns et al (1997). The members of this tribe show specialized organs in the caudal fin of the males that vary from the presence of modified scales to the presence of hypertrophied tissues apparently of glandular function (Malabarba & Weitzman, 1999, 2000; Malabarba et al, 2004). The Mann-Whitney test was used to determine if absolute fecundity and body size of the females of O. pequira collected in the first reproductive period (spring) differed from those of females collected in the second reproductive period (summer)
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