Sex and Size Structure of Roach (Rutilus rutilus) and Bleak (Alburnus alburnus) Populations in Zhrebchevo Dam

The purpose of the present study is to analyze the sex and size structure of roach (Rutilus rutilus) and bleak (Alburnus alburnus) populations from carp family (Cyprinidae) in Zhrebchevo Dam. The survey was conducted in February 2013. The main task of the Dam visit was to collect representatives of all fish species active in the season and caught by the fishermen. In order to obtain a representative samples of fish, was taken specimen of each species, fishermen had caught. Were got 26 sexually mature roach (7♂ and 19♀) and 27 sexually mature bleak (12♂ and 15♀). A specific feature of roach sex structure is the bigger number of females (73.08%) than males (26.92%) in the population. In the bleak (Alburnus alburnus) population the number of males and females is almost equal with a small predominance of the females (55.55%) over the males (44.45%). The analysis of the size structure of roach and bleak populations inhabiting Zhrebchevo Dam indicates that males are relatively smaller than females and these differences apply with accuracy of (P≤0.001) for the total body length and with accuracy of (P≤0.01) for the live weight of the examined fish species. The trend is the same within the bleak population where the differences apply with accuracy of (P≤0.01) for the total body length and with accuracy of (P≤0.001) for the live weight. Bleak's yield is 88% which is higher than the one of the roach - 16%.