Reproduction of fishes of the Verde River, upper Paraná River Basin, Brazil

Abstract

Abstract. Introduction: Understanding the various aspects of the reproductive biology of fish is a key step towards applying effective strategies for sustainable management of fishery resources. Objective: We aimed to evaluate the sex ratio, reproductive period and lengths at first maturity for 30 fish species caught in the Verde River, upper Paraná River Basin, Brazil. Methods: Fish were sampled monthly from November 2010 to March 2011 and from October 2011 to February 2012, and sampled quarterly from May to August in 2011 and 2012; totaling 14 samples. Fish were measured and weighed in the laboratory. In addition, gender and gonadal developmental stage were identified macroscopically. Subsequently, the sex ratio was determined and significant differences were tested using the chi-square (χ²) method. The reproductive period was determined with the use of gonadal developmental stages and the gonadosomatic index. Lastly, length at first maturity was estimated only for the species that presented individuals with sufficient immature and mature gonads to adjust the model. Results: Of the captured individuals, 51.5 % were male, and 48.5 % were female. Fifteen species showed significant differences in their sex ratios. The reproductive period for most species occurred from October to February, with reproductive peaks in November, December and January. The length at first maturity was estimated for only five species, including Salminus brasiliensis, a keystone species. Conclusions: The sex ratios revealed that for many species, there is a predominance of males over females, which was not expected for this parameter. The reproductive period follows the same pattern observed in Neotropical fish. However, it is noteworthy that some species are starting their reproduction in August.

Reproductive biology of endemic sailfin silversides fish Telmatherina antoniae Kottelat, 1991 in Matano Lake, South Sulawesi

“…The difference in sex ratio can be caused by several factors, including abundant food availability that is used by the female fish, the difference in growth rate [19], and the mortality between male and female fish [20]. Balanced conditions generally occur in more stable environments with minimal human influence [21]. The sex ratio is said to be balanced at a 1:1 comparison value, as the balanced sex ratio condition indicates the stability of the fish population in nature.…”

“…This is in contrast to the study of [5], that female sailfin silversides (total length = 70 mm) undergo an earlier gonad mature phase than male fish (total length = 77 mm). The length at first maturity is thought to be influenced by the physiological properties of fish, age, behavior, distribution, and environmental conditions [21]. Even in the same species, the length at first maturity can be different because of environments and geographical conditions [22].…”

REPRODUCTIVE ASPECT OF TINY SCALE BARB, Thynnichthys thynnoides (BLEEKER, 1852) AT RUI RIVER, PERAK, MALAYSIA

“…In fishery management practices, estimation of fish sex ratio (i.e., ready-to-mate females to ready-tomate males or vice versa (de Jong et al, 2009;Maskill et al, 2017) may assist in determining whether the population is in a standard or abnormal condition. A healthy fish population in its natural habitat usually has a sex ratio of 1:1 (Neves et al, 2020). However, biological, environmental, and behavioral changes such as water temperature, water velocity, ecological hazards, competition level, mate selection, migration phase, the vulnerability of females to their predators, and aggression could drive fluctuations in the sex ratio of the fish population (Neves et al, 2020).…”

“…A healthy fish population in its natural habitat usually has a sex ratio of 1:1 (Neves et al, 2020). However, biological, environmental, and behavioral changes such as water temperature, water velocity, ecological hazards, competition level, mate selection, migration phase, the vulnerability of females to their predators, and aggression could drive fluctuations in the sex ratio of the fish population (Neves et al, 2020). Therefore, the estimated sex ratio would be better understood according to their breeding behavior.…”