Gut contents of bighead carp (Aristichthys nobilis) and the processing and digestion of algal cells in the alimentary canal.
Bighead carp is one of the most important freshwater filter-feeding fish of Chinese aquaculture. In recent decades, there have been a number of contradictory conclusions on the digestibility of algae by bighead carp based on the results from gut contents and digestive enzyme analysis or radiolabelled isotope techniques. Phytoplankton in the gut contents of bighead carp (cultured in a large net cage in Lake Donghu) were studied during March-May. In biomass, the dominant phytoplankters in the fore-gut contents were the centric diatom Cyclotella (average 54.5%, range 33.8-74.3%) and the dinoflagellate Cryptomonas (average 22.8%, range 6.8-55.8%). Phytoplankton in water samples were generally present in proportionate amounts in samples from the fore-guts of bighead carp. The size of most phytoplankton present in the intestine of bighead carp was between 8 and 20 µm in length. Bighead carp were also able to collect particles (5-6 µm) much smaller than their filtering net meshes, suggesting the importance of mucus in collecting small particles. The examined change in integrity of Cyclotella upon passage through the esophagus of bighead carp indicated that disruption of algal cell walls is principally by the pharyngeal teeth, and explains previous contradictory conclusions.