Fin Erosion in Intensively Cultured Walleyes and Hybrid Walleyes

Fin erosion was observed in two cohorts of walleyes Stizostedion vitreum and one cohort of half-sibling hybrid walleyes (walleye × sauger S. canadense) raised from hatch in fiberglass tanks. All size and relative fin length (fin length/standard length) differences between stocks within the same year were statistically significant. Morphometric measurements of the 1993 cohorts of walleyes and half-sibling hybrids were made in 1994 at 414 d posthatch (dph). Caudal fin erosion was more severe in walleyes than in hybrids, but hybrid walleyes had more severe pectoral and pelvic fin erosion. Also, compared with mean relative fin lengths from reference sources, pelvic fins of walleyes were about 45% of the reference values versus 28% for hybrids; relative pectoral fin length for walleyes was 78% but only 28% for hybrids; relative caudal fin length was 94.9% for walleyes and 130% for hybrids. In the 1995 cohorts, we compared measurements of 206-dph walleyes from Spirit Lake, Iowa (SLW), with 227-dph domestic stock from London Fish Hatchery, London, Ohio (OHW). The most severe fin erosion was in the OHW stock, for which relative caudal fin length was 75% of reference value, pelvic fin lengths were 63%, and pectoral fin lengths were 36%. The problem of fin erosion is important because it can reduce vigor and decrease growth, lead to the loss of osmoregulatory control or septicemia and secondary infections, and reduce the value of the fish for stocking or marketing. Fin erosion in other species has been attributed to disease, nipping, and physical abrasion on hard surfaces. In the present study, columnaris disease caused by Flexibacter columnaris seemed to be the most likely cause of fin erosion.