Frontiers in Marine Science (Oct 2015)
Relationship between gill raker morphology and feeding habits in filter-feeding Asian carps (Hypophthalmichthys spp.) in Lake Balaton (Hungary)
Abstract
Bighead carp (Hypophthalmichthys nobilis) and silver carp (H. molitrix) are freshwater planktivorous fish originated from Eastern Asia, which were introduced all over the world. Previous studies suggested that bighead carp with comb-like gill rakers feeds mainly on zooplankters, while silver carp with sponge-like filtering apparatus filters smaller particles and the majority of its diet is composed of phytoplankton. In Lake Balaton, however, the Asian carp stock is formed by the hybrids of these two species, whose filtering apparatus varies within the whole range from comb-like to spongious structures. Since there is no information on how hybridization affects the feeding efficiency of Asian carps, we analysed the relationship between gill raker morphology and food size-distribution in hybrid Asian carps, in Lake Balaton. Filtering apparatus of each sampled fish (n=26) was characterized by two morphological indexes, assumed to be indicative of feeding efficiency. First, the effective area of the filtering apparatus was measured relative to the respiration organ; the width of the gill raker relative to the width of the gill-filaments was determined at the centre of the gill-arch. Second, density of pores on the outer surface of the spongy gill raker areas was counted, while zero scores were given to comb-like areas. Feeding of fish was determined from the filtrate suspension collected directly from the inner surface of gill rakers. Diet items were identified, counted and classified into three phyto- (> 40 μm, 40−10 μm, 1.3 mm, 1.3−0.4 mm, < 0.4 mm) size groups. Contrary to our expectations, no significant relationship was found between the gill raker morphology and phyto- and zooplantonic food size distribution in hybrid Asian carps. Thus, the Asian carp stock, consisting of hybrids with variously mixed phenotypes, consumes similar food, but seasonality has a significant impact on their diet.
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