Using the back calculation to study of the age and growth of Caspian trout (Salmo Caspius)
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The aim of the present work was to study the growth and age structure of Caspian trout, Salmo caspius. A total of 43 and 101 individuals were captured from the Cheshmehkileh River, Tonekabon, Iran, for back-calculation and biometric parameter studies, respectively, including measurements of length, weight, and age. The minimum and maximum ages determined were 4 and 7 years, while the 5-year age group showed the highest frequency, and the 6- and 7-year groups showed a remarkable pattern.
The mean length and weight of captured individuals were 69.2 ± 6.2 cm and 3323 ± 677 g, respectively. Based on the back-calculation method in 2014, the mean lengths of 1-, 2-, and 3-year-old fish were 18.98 ± 3.5 cm, 30.5 ± 7.24 cm, and 41.7 ± 9.1 cm, respectively, all of which were below the maturity age and therefore generally did not approach coastal waters for spawning.
Moreover, males possessed larger body sizes, which might indicate better growth performance; however, females showed greater prevalence and frequency. Growth parameters such as the growth coefficient (K) and asymptotic length (L∞) were measured as 0.18 and 104 cm, respectively, while the growth performance index (Ø’) was calculated as 3.289, indicating negative allometric growth. The values of L∞ and K for Caspian trout demonstrated an acceptable range and suitable growth performance.
The study also suggested that excessive hatchery rearing may reduce the fitness of hatchery fish in the wild. Therefore, further empirical studies are needed to clarify whether hatchery stocking is beneficial or harmful to natural populations.
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