Growth Parameters of Rainbow trout (Oncorhynchus mykiss) escaped from sea cages in the coast of southern Caspian sea

Rainbow trout is one of the 100 exotic invasive species in the world, and the biological characteristics of evaporated specimens of marine cages on the coast of Mazandaran including sex ratio, length and weight relationship, and growth are necessary. In order to study the rainbow trout growth parameters, 90 specimens of this species were collected from October 2017 to May 2019 from catching bony fish from west to central coast of Mazandaran, in order to study the male sex ratio was 1.04 and was approximately equal. The mean length and weight of fish caught were 31.82 ± 1.03 cm and 566.05 ± 44.02 grams, respectively. The caught specimens consisted of 4 age groups 1+ to 4+ and the 1+ group was the highest, accounting for more than 35.6% of the specimens. The growth pattern of this species allometric negative was W= 0.038*L2.7. In different sexes, allometric was negative, so that the length and weight relationship was obtained in the female sex W=0.07*L2.6 and in the male male W=0.11*L2.4. The maximum estimated length (L∞) for this species was 68.98 cm and its other growth parameters in the Van Bertalanffy equation Lt = 78/68 {1-EXP[- 0/67 (t + 0/05)]}. The results of this study showed that this species does not grow well in the Caspian Sea and the most frequent is the age group under one year old. Fish escape from cages in different years has occurred and the possibility of initial life and compatibility with the Caspian Sea ecosystem for this exotic species with its environmental conditions is provided in terms of salinity, temperature and nutrition.