Summary
Lateral-body bar marking differences can be used for identifying young-of-year bluegills and pumpkinseeds. The young-of-year of both species were reared in the laboratory from eggs and examined weekly for lateral-body bar pigmentation development. Pumpkinseeds were found to develop spots between the bars when they had reached the size of 25 mm while bluegills never developed spots but had distinct body bars by 24 mm. Examination of older fish of both species from three natural populations confirmed these differences as species typical.
Methodology
Eggs of both species were collected from Lake Opinicon, Ont. during the spawning season and brought into the laboratory of the Queen's University Biological Station for rearing. To ensure that parental crosses were pure (hybrids occur with a frequency of approximately 5% in the lake (Clark 1980)), nests were monitored throughout the courtship and spawning phase. Eggs were then collected-from nests known parental spawnings. Rearing aquaria were supplied with a continuous flow of lake water which maintained water temperature to within lCO of ambient. A natural photoperiod was maintained. In addition to the laboratory-reared fish, fish were also collected from Lake Opinicon and examined daily from the first week of August. This is the approximate time when young-of-year centrarchids appear in the littoral zone of Lake Opinicon (Keast 1980). Thirty-seven young-of-year, 100 yearling, and 30 older bluegills and pumpkinseeds were collected and examined. Ten young-of-year, 30 yearling, and 20 older fish were collected from the Cataraqui River, a slowly flowing system with both pumpkinseeds and bluegills present. Pumpkinseeds were also collected from Atkens Lake which does not contain bluegills (Complak, unpublished data) and represents a different drainage system from the other two areas examined. Twenty-five yearling and 40 older fish were examined. Since Lake Opinicon is on the northern edge of the range for bluegills (Scott and Crossman 1973), it was not possible to examine water systems where only bluegills occur.