Abstract:
Filter-feeding bighead carp (Hypophthalmichthys nobilis) and silver carp
(Hypophthalmichthys molitrix) are globally important species in terms of higher fish
production and suitability in biological control of eutrophication. Previous studies on
feeding ecology of these two species were mainly based on gut content analyses of fish
in confined and controlled environments. By using 8I3C and SI5N stable isotope ratios
and Bayesian mixing models an attempt was made to analyze the trophic relationships
among freely foraging bighead and silver carps, and their potential food items in four
trophically different lakes in China. In each lake, three study sites were selected. At each
study site, trophic condition was assessed using habitat characteristics. Fish were
collected from gill nets and fke nets, to retrieve dorsal, white muscle tissue for stable
isotope analysis. Zooplankton, phytoplankton, fine particulate organic matter and
detrital plant particles within the sediment were collected as potential food types to
analyze SI3C and SI5N values. Stable isotopic values of food sources were significantly
different among four lakes (Kruskal-Wallis; P< 0.005). Habitat characteristics were
significantly different among four lakes and hot (summer) and cold (winter) sampling
periods (2-way ANOVA; P< 0.05). Bayesian mixing models revealed that both fish
species had similar diets within lakes, and where dietary shifts occurred, both species
displayed dietary shifts simultaneously. Diet was generally based on plankton, however,
detritus was the main food in the lake subjected to urban pollution. Diet of both species
shift towards phytoplankton when algal biomass was high in the lake with artificial
fertilization. Niche breadth was variable but in general clear size-based resource
partitioning was observed, with bighead carp preying more on zooplankton and
occupying a higher trophic position, and silver carp feeding more on phytoplankton.
Isotopic nidhe tend to overlap in the habitats with high non-algal turbidity, and marked
with lower conductivity and pH values.
