Growth parameters and phenotypic variation of Kawakawa Euthynnus affinis (Cantor, 1849) in the Persian Gulf (Hormozgan waters)

Cosidering the ecological and fisheries importance of Tuna fish in the unique environment of the Persian Gulf, it is crutial to identify different stocks of this fish for practicing sustainable fisheries management. This study was conducted to evaluate the growth parameters and identify different stocks of Kawakawa E. affinis in three regions of Hormozgan waters including Qeshm, Abu Musa and Bandar Kolahi using geometric morphometrics and mersitic featurs. Our results showed that there is a relatively high correlation between length and weight of Kawakawa in all the three study areas. The b values calculated based on the exponentioal correlation of length and weight indicated that Kawakawa followed a negative allometric growth in all thee areas including Qeshm (b=2.8369), Abu Musa (b=2.5605) and Bandar Kolahi (b=2.6456). The values of condition factor were higher than 1.0 in all the three studied areas. The results from the CVA analysis showed a significant difference between the stocks from Abu Musa and Qeshm in terms of body shape. The results of thin plate spline in deformation grid network indicated that the highest variations among the located landmarks were in body height at abdominal area, tail peduncle and anal finlets, as well as in the head length at the posterior end of gill operculum. More specifically, the fish from Abu Musa had higher body height and tail peduncle compared with that observed in the fish from the other locations. There was a very low variation among the three araes in terms of meristic characters . However, the number of spines on first dorsal fin was significantly more than the stocks of Qeshm and Abu Musa. In conclusion, the results of this study revealed a high phenotypic variation in many morphometric characters while the meristic characters showed lower variation. High phenotypic variation in morphometric characters in Kawakawa fish living in the Persian Gulf along Hormozgan waters is likely due to differences in habitats, reproduction, migration pattern and even feeding conditions.