Digestive enzyme pattern of two stomachless filter feeders, silver carp, Hypophthalmichthys molitrix Val., and bighead carp, Aristichthys nobilis Rich.

Activities of digestive enzymes (trypsin and amylase) of microplanktophagous silver carp, Hypophthalmichthys molitrix, and macroplanktophagous bighead carp, Aristichthys nobilis, were investigated in relation to pH in 10 different segments of the gut. In addition, the possible existence of ‘classical’ lysozyme in both species and cellulase in silver carp were scrutinized, but no activities were detected. Tryptic and amylolytic activities decreased sharply from fore‐gut to hind‐gut indicating an efficient reabsorption mechanism. Trypsin and amylase of both species had a pH optimum at 8.3 and 7.0 respectively. The relatively low pH of 6.4 in the fore‐gut of silver carp did not support an efficient operation of these enzymes, which was compensated by a higher enzyme concentration as compared to bighead carp. The latter, however, showed a higher pH of 7.3 in the fore‐gut and thereby maintained similar activities as silver carp. The distinction of herbivorous and omnivorous fish in terms of digestion mechanisms is discussed.