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Investigation of age structure and growth and reproductive indices of Gambusia holbrooki (Girard, 1859) in the Gamasiab River (Kermanshah Province) in summer and autumn
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Ali Reza Radkhah   , Soheil Eagderi * , Hashem Nowferesti |
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Abstract: (84 Views) |
| The aim of this study was to investigate the age structure, growth and reproduction indices of mosquitofish (Gambusia holbrooki) as a non-native and invasive species in the Gamasiab River (Kermanshah Province). For this purpose, a total of 131 specimens were caught by electrofishing during two sampling seasons (summer and autumn) in 2022. Biometric characteristics including total length, standard length, total weight and gonad weight were measured separately for males and females. Scales and operculum bones were used to determine the age of specimens. Length-weight relationship, growth pattern, condition factor (K), gonadosomatic index (GSI) and relative fecundity were calculated for both sexes in each season. The results showed that the maximum observed age was 1+ years for males and 2+ years for females. The 2+ age group was observed exclusively in females with frequency of 10.3% in summer and 6.0% in autumn. The sex ratio (female: male) was 1:1.03 in summer and 1:1.18 in autumn, showing no significant difference (P> 0.05). The b parameter in length-weight relationship for males and females was 3.17 and 3.40 in summer, and 3.12 and 3.38 in autumn, respectively, indicating positive allometric growth pattern in all groups. Condition factor was above one in both sexes and seasons (range 1.09 to 1.36). GSI was significantly higher in females than males, with higher values in summer (15.82) compared to autumn (12.23). Relative fecundity of females was higher in summer (31.20 eggs.g⁻¹) than in autumn (27.85 eggs.g⁻¹). The highest mean length and weight were observed in 2+ year old females in summer (48.20 mm and 1.85 g). In general, favorable condition factor and high reproductive potential peaking in summer provide a picture of the successful biological invasion of G. holbrooki in the Gamasiab River. This study can be used for population management of this non-native species and conservation of aquatic ecosystems in the region. |
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| Keywords: Gambusia, Age structure, Growth pattern, Gonadosomatic index, Fecundity, Gamasiab River |
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Type of Study: Research |
Subject:
Special
Received: 2021/05/25 | Accepted: 2026/02/27 | Published: 2026/02/27
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