Vízügyi Közlemények, 1994 (76. évfolyam)

2. füzet - Csányi B.-Németh J.-Gulyás P.: A domináns halfajok legfontosabb táplálkozási kapcsolatai a Kis-Balatonban

210 Csányi B

.-Németh J.-Gulyás I'

. Feeding relationships among the dominant fish species of the Kis-Baluton wetland by Béla CSÁNYI, biologist, József NÉMETH, chemical & agricultural engineer and Dr. Pál GULYÁS, professor in biology-geography Researchers of the Institute for Water Pollution Control of the Water Resources Research Centre VITUKI started the investigation of the Und phase of the Kis-Balaton Protecting System (a rehabilitated/reconstructed marshland). As part of the hydrobiological monitoring programme the nourishment-hiology of the dominant fish specics and of the planktonic and benthic communities of the recently inundated new wetland (Figure 1

), the so called Lake Fenéki and the Zalavár Waters, was investigated (Table I). The objective of the investigation was to reveal those relationships of the food web of this area that have not yet been determined. Trial fishing operations of the summer period on the largest open water surface of the inundated area, the Zalavár Waters (Figure 1), resulted in catches consisting solely of the young age groups of Carassius carassius L. and Scardinius eiythrophthalmus L. In the fall this was completed by some young and several years old specimens of the Carassius auratus gibelio (Table II). The fish fauna of the Zalavár Waters is thus, very poor, characterized bw populations of low number of species. Nevertheless, substantial changes can be expected due to the recently established connection with the Lake I lidvégi (the first phase of the reservoir system) and with the River Zala, in terms of immigrating new species (Figure J). Phytoplankton, including benthic phytoplankton, were investigated at several sampling points of the Zalavár-Water. On the basis of phytoplankton investigations the water of Zalavár-Water proved to be meso-cutrophic. The extremely poor phytoplankton species were dominated by diatoms (Pennales) and bluegreens (Hormogonales). Having the similarity structure of the qualitative algae taxon lists analyzed it can be stated that the feeding ground of the fish species examined is the weed stock of the Fenéki Tó (Figure 1). The fish examined are feeding on algae and Zooplankton without preference. The list of taxon compiled on the basis of a complex study of macro zoobenthos consisted of a total of 78 invertebrate taxa. It can be stated that the benthic fauna of the Felső Open Water, the Zalavár Water and the northern areas densely overgrown by reed consist of many common species. The macroscopic invertebrate community of these waters contains several rare wetland species. Aquatic weeds are the essential habitat for almost all of the taxa identified. They are rarely found in the sediment, likely due to the lasting oxygen depletion. Consequently the fish of the Zalavár Waters feed mainly on benthic species living among the aquatic vegetation. Analyzing the feeding relationships of the three fish species identified, several similarities with the results of the Lake Hidvégi were found. The digestive system of the Carassius auratus gibelio contained much fine sediment and fibrous vegetation masses. Of the macroscopic invertebrate taxa Chironomida larvae and, in a single occasion, the water snail Planorbisplanorbis were found in greater quantities. In the gastro-intestinal system of the juvenile Carassius auratus gibelio contained few Copepoda and Cladocera only. These species live in the biotekton and on the surface of the bottom sediment. Older age groups consumed equally large quantities of Copepoda, Cladocera and Ostracoda. Among the fish species examined the Carassius auratus gibelio consumed the richest variety of Zooplankton. Of the Scardinius eiythrophthalmus L. only four young specimen were found in the Zalavár Waters. Food organisms were found only in the digestive system of two of these fishes, consisting exclusively of the larvae of larger aquatic insects. Similarly to the case of the Lake Hídvégi (the upper reservoir) their menu consisted mostly of the larvae of Aeschnida, Chironomida and of the Corxida. These benthic taxa are commonly occurring among the macrophytes of the Zalavár Waters. The young population of the native Carassius carassius L. of the Lake Fenéki consumes substantial algae masses, Oligochaeta taxa and aquatic insects.