Effects of water level fluctuation on reproduction and spawning habits of fish species in Lake Balaton

Abstract

In 2004, the types of shoreline were estimated on Lake Balaton, such as rip-rap, reedy, concrete or grit. In the rip-rap covered parts, the rocks are rather uniform in size because they originate from quarries faces of which can be modeled as polygons. Exact area of a specific face of a rock can be determined by digital image analysis. Wetted area of the shore was estimated as a function of water level in 10 cm steps of level changes. Taking into account the reproduction characteristics of the studied fish species (Cyprinidae) the potential substrates of spawning are dominantly the shallow zones near the shoreline. The dominant type of shoreline is rip-rap with about 42% of total.. Almost all grit are has been lost in recent decades though it is the typical reproduction area of carp. The rip-rap covered shore sections are used for reproduction by species of bream. On studying the structure of fish stock we found that the dominant species were the bream, bleak and roach. Spawn samples were collected in April and June, 2006, at the shoreline area near Tihany, Örvényes, Keszthely, Balatonberény, Badacsonytomaj, Szigliget, Paloznak and Balatonfüred. The estimated specific number of spawn was between 110 and 2196 pieces/m².Tthe lowest figure was found near Szigligetwhile the highest near Keszthely. The wet rocky substrate, disappears almost everywhere around the lake when the water level decreases to and below 30 cm. The lake shows substrate deficit when the water level is -50 cm that may cause some problems in the reproduction of species of bream, so it would be very important that to open the Zala and Little Balaton Water Protection System in front of the spawning fish. The reproduction area can not sustain the spawn-taking of any fish (i.e.: carp, wels, asp) when the there are some suitable area and the water level is good. The inlets of Balaton could play more important role in the rising of new generations.