Bream in the rivers of the Oka Basin

Abstract

Bream in the river systems of the Oka basin is widespread, including tributaries of the third order. This representative of cyprinid fish is numerous mainly in the most full-flowing rivers with a length of more than 500 km. The age composition of bream from net catches in the Oka over a long period of observations did not exceed 14 age groups, and fish older than 12+ were not recorded in the Klyazma and Moscow rivers. The growth of bream in the Oka, Klyazma, and Moscow rivers does not differ significantly on average, due to seasonal bream migrations and similar feeding conditions. The main factor influencing the decrease in the number of bream in the Oka and Klyazma is a long period of low spring floods, which prevents flooding of the high river floodplain and sharply reduces the efficiency of its spawning, especially in the upper reaches of the Oka and Klyazma rivers. An adaptive feature of the reproductive biology of bream in the upper reaches of these rivers is the extended spawning migration of mature fish upstream, where the ripal vegetation in riverbeds serves as a spawning substrate for it. Bream in the rivers of the Oka basin is currently a secondary object of amateur fishing and one of the main species in poaching catches.