Diet and digestion in Chinese mud carp Cirrhinus molitorella compared with other ilyophagous fishes

Ilyophagous fishes, that is, those that feed on soft sediments, are widely distributed throughout temperate and tropical freshwater and estuarine environments. Despite their abundance (they constituted over half of the ichthyomass in some systems), the role of these fishes in ecosystem structure and function has received little attention. In particular, data on diet and digestion in Cirrhinus, a genus abundant through much of Southeast Asia, are yet to be reported. In this study we examined gut contents of Chinese mud carp Cirrhinus molitorella; fish ranged from 16 to 29 cm total length and were collected from five ponds each in Wuchuan and Shunde Counties, Guangdong Province, China. Their diets were made up of sand, mud, and amorphous organic matter. Foregut samples averaged 0.226-mg ash-free dry weight (AFDW)/mg dry weight and 0.155 mg total amino acids (AA)/mg AFDW. Assimilation efficiency averaged 0.113 for AFDW and 0.153 for total AA. Compared with that in other ilyophagous fishes, digestion in Chinese mud carp is inefficient. Nonetheless, the ratio of AA (mg) assimilated to total organic matter (mg) assimilated - 0.209 - is in the range expected to support moderate growth, as has been reported for this species. Review of the literature on ilyophagous fishes reveals four groups characterized by different gut morphologies that each appear to be adapted to the use of relatively indigestible diets. The extremely long, undifferentiated alimentary canal in Chinese mud carp and related species is the simplest of these, and its relative inefficiency may be related to this simple morphology. © Copyright by the American Fisheries Society 2006