USGS · 1014132
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S. F. Snieszko. 1961. Hepatoma and visceral granuloma in trout. https://pubs.usgs.gov/publication/1014132
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The contents of stomachs from 1,485 white perch, 218 rock bass and 1,399 yellow perch collected in eastern Lake Ontario from May to October in 1972 and in May 1973 were examined. All three species fed primarily on amphipods, but they also ate chironomids and trichopterans regularly. Rock bass ate more trichopterans than chironomids, whereas white perch and yellow perch ate more chironomids. Snails and crayfish were significant items in the diet of rock bass, but occurred infrequently in stomachs of white perch and yellow perch. White perch and yellow perch frequently ate fish eggs during early summer, but rock bass seldom ate fish eggs. Fish were important in the diets of white perch longer than 300 millimeters and rock bass and yellow perch longer than 200 millimeters. Similarities in the diets of fish 1 year old or older suggest that the potential for competition between white perch and yellow perch is greater than that between rock bass and either white perch or yellow perch.
To test the reliability of current techniques, five biologists appraised the ages of 200 quail from a random sample of wings collected during the 1952-53 hunting season in Alabama. Attempt was made to distinguish adults from juveniles, to ascertain the stage of post-nuptial and post-juvenile molts, and to estimate the age of juveniles according to days or weeks. Three 'problem' wings in this sample had molt characteristics somewhat eauallv divided between adult and juvenile classes; two wings called 'questionable' had all molt characteristics except one of either age group. A 3.5 per cent disparity occurred between investigators in their classification of adult and juvenile age groups. This included not only 'problem' and 'questionable' wings, but also 'obvious errors.' Individual differences were greater than 3.5 per cent but cancelled out. This study emphasizes the need of working with large samples of birds of a known age in order to know more concerning molt variations. Until aging techniques can be refined, it is believed that investigators should be fully familiar with existing methods and their weaknesses. Also, it appears important that reports on aging should indicate clearly the techniques used.