Food habits, feeding behaviour and impact of triploid bighead carp, <i>Hypophthalmichthys nobilis</i>, in experimental ponds

Abstract

Food of sterile triploid bighead carp, Hypophthalmichthys nobilis , was examined in ponds receiving water from a hypereutrophic take in Florida. No distinctive seasonal changes in food composition were found. The fish fed selectively on Botryococcus braunii Kuetzing, a large nuisance algal species, which constituted 61% of the volume and 50% of the dry weight of the food. Zooplankton was highly selected, but constituted only 3% of the food volume because of the low zooplankton density in the ponds. The remaining proportion of food consisted mainly of blue‐green algae. Final fish biomass was low, ranging from 60 to 97 kg ha −1 in individual ponds. Low biomass was due to slow fish growth and high fish mortality. Despite low biomass, the fish lowered the ratio of blue‐green/green algae in the ponds and tended to lower phyto‐ and zooplankton abundance.