Summary
A comparative study of the diets of five year classes of perch in Lake Opinicon showed Year class 0 to be mainly Cladocera feeders, the Year class II to take a diversified range of insect larvae, whereas from Year class V onwards Anisoptera nymphs, decapods, and fish dominated the diet. Sizes of the dominant food items changed strikingly with growth, prey weights of 0.1, 0.5-1.0, and loo-250 mg predominating in these three age groupings. There were marked month to month changes in types and proportions of different prey consumed. Overall and month to month feeding overlaps between consecutive year classes were considerable, most values ranging from 0.68-1.0 by the Levins formula. However, diet overlap dropped sharply with increasing age gap. Month to month dietary changes and year class differences were interpreted relative to benthic invertebrate abundance cycles. Months of increased diet overlap were characteristically those when favored prey types peaked, thereby simultaneously attracting several year classes to them. Hence increased diet. overlap is not necessarily an indicator of increased intraspecific competition. Habitat differences between the year classes of perch in Lake Opinicon were partial and concerned mainly the smaller, and larger, fish relative to those in the middle size range.