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<p>This study aimed to investigate the biological traits, growth patterns, and reproductive characteristics of <i>Gambusia holbrooki</i> inhabiting Golestan Dam, located in the main watershed of the Caspian Sea in Golestan Province. A total of 278 specimens were collected using electrofishing techniques. Fish sampling was conducted over a seven-month period, from February to August 2022, at two sampling stations within Golestan Dam (Table&#xa0;1; Fig.&#xa0;2). All captured specimens were preserved in 5% formalin and transported to the laboratory for further analysis. After sex determination, the specimens were analyzed separately by sex as well as collectively as a whole population. Total length was measured to the nearest millimeter for growth and mortality assessments, and length-class intervals were determined using Sturges’ formula (Sturges, 1926). Various biometric parameters, including total length, standard length, total weight, and gonad weight, were measured for both male and female specimens. The study focused on analyzing length–length and length–weight relationships (LWR), growth patterns, condition factor (K), gonadosomatic index (GSI), and relative fecundity for each sex. Overall, females were larger than males, highlighting clear sexual dimorphism in this species. The length–weight relationship analysis indicated positive allometric growth in females and negative allometric growth in males, with b-values of 3.51 and 2.52, respectively. The condition factor (K) was higher in females (1.84) than in males (1.29), suggesting that <i>G. holbrooki</i> thrives under favorable environmental conditions in Golestan Dam. Similarly, the gonadosomatic index (GSI) was markedly higher in females (30.56) compared to males (19.65), indicating a superior reproductive condition in female individuals. Furthermore, relative fecundity in females was estimated at 36.01 eggs g⁻<sup>1</sup>, reflecting a high reproductive output during the study period. In conclusion, the results of this study emphasize the reproductive success of <i>G. holbrooki</i>, as evidenced by the larger body size, higher condition factor, and elevated gonadosomatic index observed in females. These life-history traits contribute to the species’ competitive advantage and facilitate its success as an invasive, non-native species. The findings provide valuable insights into the biology and reproductive strategies of <i>G. holbrooki</i>, which can support management and control efforts in freshwater ecosystems.</p>

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An overview of the biology and population dynamics of Gambusia holbrooki (Girard, 1859) in the Golestan dam: ecological insights from the main watershed of the Caspian sea

  • 期刊论文

  • 发表日期：

    2026年7月4日

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  • Eisa Hajiradkouchak,
  • Behzad Rahnama

摘要

This study aimed to investigate the biological traits, growth patterns, and reproductive characteristics of Gambusia holbrooki inhabiting Golestan Dam, located in the main watershed of the Caspian Sea in Golestan Province. A total of 278 specimens were collected using electrofishing techniques. Fish sampling was conducted over a seven-month period, from February to August 2022, at two sampling stations within Golestan Dam (Table 1; Fig. 2). All captured specimens were preserved in 5% formalin and transported to the laboratory for further analysis. After sex determination, the specimens were analyzed separately by sex as well as collectively as a whole population. Total length was measured to the nearest millimeter for growth and mortality assessments, and length-class intervals were determined using Sturges’ formula (Sturges, 1926). Various biometric parameters, including total length, standard length, total weight, and gonad weight, were measured for both male and female specimens. The study focused on analyzing length–length and length–weight relationships (LWR), growth patterns, condition factor (K), gonadosomatic index (GSI), and relative fecundity for each sex. Overall, females were larger than males, highlighting clear sexual dimorphism in this species. The length–weight relationship analysis indicated positive allometric growth in females and negative allometric growth in males, with b-values of 3.51 and 2.52, respectively. The condition factor (K) was higher in females (1.84) than in males (1.29), suggesting that G. holbrooki thrives under favorable environmental conditions in Golestan Dam. Similarly, the gonadosomatic index (GSI) was markedly higher in females (30.56) compared to males (19.65), indicating a superior reproductive condition in female individuals. Furthermore, relative fecundity in females was estimated at 36.01 eggs g⁻1, reflecting a high reproductive output during the study period. In conclusion, the results of this study emphasize the reproductive success of G. holbrooki, as evidenced by the larger body size, higher condition factor, and elevated gonadosomatic index observed in females. These life-history traits contribute to the species’ competitive advantage and facilitate its success as an invasive, non-native species. The findings provide valuable insights into the biology and reproductive strategies of G. holbrooki, which can support management and control efforts in freshwater ecosystems.