MOUTH SIZE AND PREDICTED FOOD SIZE PREFERENCES OF LARVAE OF 3 CYPRINID FISH SPECIES

Mouth size was examined in larvae and juvenile of 3 cyprinid fish species: grass carp (Ctenopharyngodon idella Val.), silver carp (Hypophthalmichthys molitrix Rich.) and bighead carp (Aristichthys nobilis Rich.). A linear relationship was found between mouth size and the total length of fish, from the initial exogenous feeding stage up to 20-30 mm. Based on the mouth size, the size of the prey which could be consumed was calculated assuming 45.degree. of mouth opening for optimum prey width and 90.degree. for maximum prey width. Food particle size considered to be suitable for commencement of feeding was 50-90 .mu.m for silver carp larvae, 90-150 .mu.m for grass carp larvae and 150-270 .mu.m for bighead carp larvae. These criteria can be applied to moving rotifers and nauplii as well as to the motionless particles of compound, dry diets.