Occurrence of sterile North-East Arctic cod individual

Abstract

Based on histological analysis, cod individuals of older age groups that completely lost their reproductive capacity due to age-related gonads' degeneration have been considered. Such individuals have been found among both females and males. It has been revealed that in the gonads of sterile fish the replacement of gametes with connective tissue is taking place. According to the obtained data, the portion of sterile fish in samples among females of more than 100 cm has reached 2.2 %. The analysed sterile individuals are characterized by the drastically low gonadosomatic index while gepatosomatic index is mostly above the average. The reasons of age related sterility of the Barents Sea cod have not been discovered yet. The main role of age related fish reproductive condition is considered to be linked to hormonal regulation distortion of sexual cycle. Studying the distortion in the cod reproduction resulting in spawning skips or fish sterility is believed to be significant not only in theory, but in practice as well. Mature females' biomass is usually applied as reproductive potential indicator. However, the reproductive disorder leading to spawning skips affects reproductive abilities of the species that should be taken into account while estimating total allowable catches. In order to monitor abundance of sterile individuals of the Barents Sea cod, it has been proposed to add its maturity scale with VII stage for fish without reproductive capacity.

Keywords

• cod
• the Barents Sea
• oocytes
• sterile gonads
• maturity scale