Northern Sunfish (Lepomis peltastes) Distribution in Illinois

The recent elevation of Lepomis peltastes (Northern Sunfish) as a separate species from L. megalotis (Longear Sunfish) has resulted in an incomplete understanding of the species' distribution in Illinois, as most occurrence records cannot differentiate the 2 species. We evaluated Northern Sunfish and Longear Sunfish specimens to identify morphological characteristics that could differentiate the 2 species; relative body depth, relative opercular flap length, and pectoral fin ray count were most useful. We reevaluated 867 Longear Sunfish specimens from the Illinois Natural History Survey Fish Collection and identified 103 as Northern Sunfish. Based on distribution of these specimens, it is probable that Northern Sunfish occur in 14 basins in the eastern half of Illinois, a range that extends farther south than was previously estimated.