Relationship between gill raker morphology and feeding habits of hybrid bigheaded carps (Hypophthalmichthys spp.)

Bigheaded carps and especially silver carp have been considered as an effective biological control for algal blooms, thus were introduced to several countries in the last decades, including Hungary. Our aim was to explore the feeding habits of bigheaded carps in Lake Balaton (Hungary), where the stock consists mainly of hybrids (silver carp x bighead carp). We examined the relationship between filtering apparatus (gill raker) morphology and size-distribution of planktonic organisms in the food. We failed to find any significant relationship between gill raker parameters and plankton composition in the filtered material. Bigheaded carps with various types of gill rakers consumed food within the same size- spectrum, independently of the rate of hybridization. However, the linkage between the proportion of different planktonic size classes in the water and in the diet of fish was detectable in case of both phytoplankton and zooplankton consumption, suggesting that the seasonally variable availability of different food items was an important factor in determining the food composition of bigheaded carps. We can deduce that bigheaded carps consume high amounts of zooplankton to meet their energy requirements, and the diet overlap among bigheaded carps and other planktivores may exert negative effects on native fish populations.