Seasonal Variation in Food and Diel Periodicity in Feeding of Northern Largemouth Bass, Micropterus S. Salmoides (Lacepede), in an Oklahoma Reservoir

Food habits of 810 northern largemouth bass, 91-2724 g total weight (age groups 0-7) were determined from collections made June 1968 through November 1969 in an 808-hectare, Oklahoma reservoir. Bass were colIected by traversing the shoreline with an electrofishing apparatus and bass stomach contents observed with a gastroscope. Fifty-five percent of all bass stomachs were empty. Similar observations over a wide geographic area were reviewed and the suggestion was made that 56% occurrence of empty stomachs may be used as a guide to evaluate availability of forage for largemouth bass. Bass stomachs contained mostly crayfish and gizzard shad. Gizzard shad and partially digested fish were found in 31.1% of 810 fish, whole and partially digested crayfish were found in 13.9% of the bass. Bass swallowed crayfish and gizzard shad tail-first 96.8% and 33.5% of the time, respectively. Orientation of the prey in bass stomachs did not vary with size ofthe bass. In 1969. largemouth bass in Lake Powell, Lake Carl Blackwell and Bull Shoals spawned in the last week of April, the coincidence appears to be related to similar photoperiod at the same latitude. Variation in percentage of empty stomachs preceding, during and after the spawning season suggested that bass, probably the males, may reduce feeding during the two week interval when they are guarding the eggs and prelarval fish. Judging from occurrences of empty stomachs, bass in this lake generally fed from midmorning through afternoon rather than between evening and morning.

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