First Food of Larval Yellow Perch, White Sucker, Bluegill, Emerald Shiner, and Rainbow Smelt

Abstract

Entire digestive tract contents from larval yellow perch [Perca flavescens (Mitchill)], white sucker [Catostomus commersoni (Lacepede)], bluegill (Lepomis macrochirus Rafinesque), emerald shiner (Notropis (atherinoides Rafinesque), and rainbow smelt [Osmerus mordax (Mitchill)], along with plankton samples taken concurrently with fish samples, were identified and counted. Food selection was calculated by use of Ivlevˈs electivity index. First food of yellow perch from an eutrophic lake were copepod nauplii and cyclopoid copepods; after fish reached 11 mm in length Bosmina coregoni was the dominant food. Yellow perch from an oligotrophic lake fed first on the rotifer Polyarthra, and to a lesser extent on copepod nauplii; after fish reached 11 mm cyclopoid copepods became the most important food items. Rotifers contributed an important portion of the early diet of white sucker; copepod nauplii and Cyclops bicuspidatus provided the remainder of the diet. Cladocerans increased in numbers after the fish reached 14 mm. Food of bluegills at the initiation of feeding consisted of Polyarthra and copepod nauplii. When fish reached 7 mm other rotifers and cyclopoid copepods appeared in the diet, and at 8 mm cladocerans become the dominant food and remained so for larger fish. Rotifers, mainly Trichocera, were the dominant food of first-feeding emerald shiners, and they remained an important food of larger fish. Copepod nauplii became a dominant food when fish reached 10 mm, and Cyclops bicuspidatus and cladocerans were important foods in fish 7 mm and larger. Algae were found in fish of all sizes, and calanoid copepods were found in fish 13 mm and larger. First-feeding rainbow smelt contained Cyclops bicuspidatus, copepod nauplii, diatoms, and green algae; C. bicuspidatus was the principal food until fish reached 21 mm. Calanoid copepods succeeded as the dominant food for larger fish. Electivity indices showed the following to be highly selected prey of fish at the initiation of feeding: yellow perch-Polyarthra and cyclopoid copepods; bluegill-Polyarthra; emerald shiner-rotifers and copepod nauplii; and rainbow smelt-Cyclops bicuspidatus and copepod nauplii. Selection of food among the fish species studied was similar. Necessary criteria of a desirable prey include small size, the inability to escape capture, close proximity to the predator, and probably attraction of the predator by swimming movements.