A comparative study of percid scales (Teleostei: Perciformes)

A survey of scales of Percina (17 spp.), Etheostoma (39 spp.), Ammocrypta (3 spp.), Crystallaria (1 sp.), Stizostedion (3 spp.), Perca (2 spp.), Gymnocephalus (2 spp.), Zingel (2 spp.), and Romanichthys (1 sp.) showed that percids can be distinguished from moronids, centrarchids, and percichthyids using scale characters. Based on limited outgroup comparisons to these families, scales of Gymnocephalus, Perca, and Stizostedion may represent the plesiomorphic condition for percids. Each has stout spines with basal plates about one-third the length of a mature ctenus. Ctenial bases have transverse processes that are ligamentously joined to those of adjacent rows, but they do not form an interlocking pattern. This feature, a scalloped anterior scale margin, posterior placement of the focus, and a more expansive ctenial field distinguish percids from the other three families. Percina, Etheostoma, Ammocrypta, Crystallaria, Romanichthys, and Zingel are distinguished from other percids by the presence of alae, basal projections of cteni that interlock with those of adjacent rows, and by reduction in secondary ossifications between the proximal radial rows. Alae may be a synapomorphy uniting these genera.