Length-Weight Relationship, Condition Factor, and Reproductive Biology of Carasobarbus luteus in Greater Zab and Lesser Zab Rivers in the Kurdistan Region- Iraq

A comparative study was conducted to evaluate certain environmental and biological aspects of Carasobarbus luteus in the Greater Zab and Lesser Zab Rivers for the first time. A total of 163 and 200 specimens were collected from the Greater Zab and Lesser Zab Rivers, respectively, between December 2022 and November 2023. In the Greater Zab River, fish lengths ranged from 133 to 267 mm and weights from 30 to 276 g. In the Lesser Zab River, lengths ranged from 117 to 309 mm and weights from 30 to 417 g. The length–weight relationship (LWR) indicated positive allometric growth in the Greater Zab River, with a b value of 3.17. In contrast, growth in the Lesser Zab River was isometric, with a b value of 2.97. The condition factor (K) in the Greater Zab River was 1.421, slightly lower than that in the Lesser Zab River, which was 1.458. Condition factor values were similar between males and females at both sites. The sex ratio was skewed toward females in both rivers, with a male-to-female ratio of 1:2.26 in the Greater Zab River and 1:2.22 in the Lesser Zab River. The gonadosomatic index (GSI) for males peaked in May, reaching 3.3 and 3.6 in the Greater and Lesser Zab Rivers, respectively, with the lowest values recorded in November (1.1 and 0.9). For females, the highest GSI values were observed in April—9.3 in the Greater Zab and 9.7 in the Lesser Zab—while the lowest values occurred in December (2.0 and 2.2, respectively). Overall, the results indicate that both rivers provide suitable conditions for the growth of C. luteus. However, individuals from the Lesser Zab River exhibited better overall condition, as reflected by higher numbers, greater weight ranges, and a higher condition factor compared to those from the Greater Zab River.