On the food of pike-pearch fry (Stizostedion lucioperca L.) in Lake Balaton in 1970

Tátrai, István and Ponyi, Jenő (1976) On the food of pike-pearch fry (Stizostedion lucioperca L.) in Lake Balaton in 1970. A Magyar Tudományos Akadémia Tihanyi Biológiai Kutatóintézetének évkönyve, 43. pp. 93-104. ISSN 0365-3005

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Abstract

Stomach contents of 690 pike-perch fry caught at four collecting sites in Lake Balaton during the summer of 1970 were analyzed by the authors and the following were established. Specimens of 11-20 mm length consume Diaphanosoma brachyurum in 60 per cent and Eudiaptomus gracilis in 18 per cent, while this ratio was 50-50 per cent in 1958. As compared to data of 1957-58, the amount of total crustaceanplankton in the stomach content had decreased to its half. It means that the deterioration of feeding possibility of fry (10-20 mm size-class) continued. According to the quality of food consumed a part of pike-perch fry surpassing 20 mm body length inhabit water areas free from reed-grass stands. This results in a displacement from the relatively narrow reed-grass stands having rich food-supply. The other part consuming rich macrofauna grows faster and change to predation in time. The “diverse growth” of pike-perch fry in Lake Balaton can be explained by this phenomenon.Based on the present studies we came to the conclusion that the bulk of previous analyses were made on groups of fry displaced to the open water. With the use of collecting technique applied in earlier the fry inhabiting open water areas were chiefly caught because of the dense reed-grass. Owing to this an inaccurate statement was put forth saying that large-sized organism is lacking in Lake Balaton being necessary during the changing period of feeding habit. According to data of the summer period of 1967 and 1972, Leptodora kindtii amounted to 0.4-1.0 per cent only in the crustacean-plankton of Lake Balaton. This is why it occurred only in an insignificant quantity in the food of fry inhabiting the open water. Authors are anxious concerning the density of fry in the littoral zone of Lake Balaton, since it is unfavourable, consequently a sharp competition may occur there.

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