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Identification of Ruffe larvae (Gymnocephalus cernuus) in the St. Louis River, Lake Superior: Clarification and guidance regarding morphological descriptions
Citation:
Peterson, Greg AND J. Lietz. Identification of Ruffe larvae (Gymnocephalus cernuus) in the St. Louis River, Lake Superior: Clarification and guidance regarding morphological descriptions. JOURNAL OF GREAT LAKES RESEARCH. International Association for Great Lakes Research, Ann Arbor, MI, 43(1):205-210, (2017).
Impact/Purpose:
The impact of invasive Ruffe (Gymnocephalus cernuus) on the ecology of Great Lakes systems is currently being studied. Reproduction and early life history data, however, may be hampered by a general lack of information regarding their early life stage morphological description. Ruffe are not included in the Great lakes Larval fish key, and existing descriptions in scientific literature are inconsistent. This has resulted in confusion and error when attempting to identify Ruffe larvae in field collected samples. Combining DNA confirmation with extensive morphological analysis, Peterson and Lietz describe the morphology of field collected Ruffe larvae and provide diagnostics to distinguish them from phenotypically similar species, supporting a more confident morphological identification.
Description:
Non-native Ruffe (Gymnocephalus cernua; family Percidae) were first detected in the Laurentian Great Lakes in 1986, and are not included in the Great Lakes larval fish key which was published several years prior to their discovery. In addition, subsequent scientific literature has inconsistently described Ruffe larvae. As a result, identification of larval Ruffe remains challenging. We used traditional morphology paired with DNA technology to develop diagnostics for Ruffe larvae collected in the lower St. Louis River, and compared them to similar species. Ruffe < 6 mm total length have myomere counts and a phenotype that more closely resemble centrarchids like Black Crappie, Bluegill and Pumpkinseed rather than percids. However, morphometrics and pigment patterns can be used to distinguish Ruffe from similar centrarchids at this size. As Ruffe larvae develop, they increasingly resemble other percids such as Yellow Perch, but can be distinguished using myomere counts and morphological features. The findings presented here clarify conflicting descriptions in the scientific literature, and provide additional data to support more confident morphological identification of larval Ruffe.
