• Keast, Allen


In Lake Opinicon, Ontario, the diet of the black crappie, Pomoxis nigromaculatus, undergoes a progressive change from one in which planktonic Crustacea and small-bodied Diptera larvae predominate (in fish of body length from about 60 to 115 mm), to a diet of insect larvae and fish (in fish 160–240 mm). Most food items prove to be midwater forms and the Diptera larvae are almost entirely Chaoborus and Procladius, which are free-swimming in the water column at night.An unusual feature is the prolonged nature of the Cladocera-Copepoda eating phase, which continues into year III and to a body length of about 160 mm. Gill-raker counts show P. nigromaculatus to have a specialized screen with 25–29 rakers on the first arch. In this it differs from cohabiting centrarchids in Lake Opinicon, Ambloplites rupestris, Micropterus salmoides, and Lepomis macrochirus, in which the rakers on the first arch number only 8–12. In these species plankton feeding is restricted to the earlier stages.