STUDIES OF CASPIAN TROUT GROWTH (Salmo trutta caspius ) BY BACK-CALCULATED FISH LENGTHS  METHODS  

The aim of this project is to study the growth and age structure in the Caspian trout, comparison with other coldwater species and check the trend of these parameters in recent years. This study was conducted during 2013 till 2015. Biometric parameters such as length, weight and age of the fish were recorded. Base on Back calculation method in 1393, the average length of fish at ages 1, 2 and 3 years old were 18.98 ± 3.5, 30.5 ± 7.24 and 41.7 ± 9.1 cm. So these age groups are under the adult age and don't approaching to near the beach and rivers for spawning behavior. Therefore, these length groups cannot be observed in catch composition.

Minimum age and maximum age of this species determined 4 years and 7 years (mean = 5.6) and the most frequency allocated to  5 age group and the frequency of 6 and 7 years has been remarkable.

The average length of salmon was 69.2 ± 6.2 cm (minimum 57 and maximum 81 cm) and the average weight was measured 3323 ± 677 g (2400 to 5600 g) in the catch composition. Growth parameters such as k, L∞ and ø' was measured 0.18, 104 cm and 3.289 respectively. L∞ and growth coefficient (K) on the Caspian trout were acceptable range, that it shows good growth the fish in the sea water.

Most of the fishes were catched from Cheshmehkileh River.  

At present, Shilat uses just the broods of the Tonekaboon region for restocking of this species, we recommend using the broods of the western region separately for rehabilitation of the stocks of this region.

Keywords: Caspian trout (Salmo trutta caspius ) - growth- age-  Caspian Sea- Iran