The study of Caspian trout Growth Salmo caspius Kessler, 1877 using back-calculated fish lengths method

The present research was conducted in order to determine age and growth of the Caspian trout (S. caspius) in Iranian coastline of the Caspian Sea (western part of Mazandaran province) from 2013 till 2015. For this purpose, biometric parameters such as length, weight and age of fifty fish individuals were recorded using back-calculation method. Based on this method, 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 respectively. As these age groups are under the maturity age, they don’t approach to near the coast lines in spawning seasons. Therefore, these groups were not observed in the catch composition. Average length of the fish 4, 5, 6 and 7 years old were determined as 53.9, 63.7, 68.6 and 74 cm respectively. In the present study, the minimum and maximum recorded age of this species were 4 and 7 years (mean=5.6) respectively, and the most frequent age group was 5 and the frequency of 6 and 7 age groups has been remarkable. The average length and weight of the Caspian trout in the catch composition were measured 69.2±6.2 cm (minimum 57 and maximum 81 cm) and 3323±677 g (2400 to 5600 g) respectively. The growth parameters including growth coefficient (K), length-infinity (L∞) and ´ø were measured as 0.18, 104 cm and 3.289 respectively. L∞ and K for the species were in the acceptable range.