Knobfin Sculpin Now Abundant in Connecticut River System

Identification

Spiny and soft dorsal fins widely connected. Pigment in soft dorsal, caudal, and anal fins highly marbled. Four pelvic fin rays, palatine teeth present and well developed. Mouth somewhat larger than slimy sculpin. Lips and throat of mature males with varying degrees of blue-green pigment, becoming very pronounced in breeding males. Knobfin sculpin is the only sculpin species in the Pomperaug River Drainage Basin, and has not been collected from any other drainage basins.

Size

Commonly 3 to 4 inches. State survey max. size 5 inches, which is the largest reported anywhere.

Distribution

Knobfin sculpins are native to the White River drainage in the southern Ozark Region of southern Missouri and northern Arkansas. The first specimen from Connecticut was collected from the lower Weekeepeemee River in 2002. Knobfin sculpins have since colonized the entire lower Pomperaug River drainage, where they have become superabundant in the entire Pomperaug River main stem, and in the lower reaches of Sprain Brook, Weekeepeemee River, and Nonewaug River. The upstream spread of this species has been limited by natural bedrock barriers on Sprain Brook and Weekeepeemee River, and by an old mill dam on Nonewaug River.

Habits

Interestingly, knobfins were not found in the smaller Pomperaug tributary brooks, seeming to prefer the habitat in the small main stem rivers. Habitat in these small rivers consists of clear, moderately cool water with gravel and cobble substrate and moderate to fast flows. They stay on the bottom, and can be found holding positions in a range of flows, from swift riffles to shallow pools. In prime habitat, they can reach high densities approaching one per square foot.

Comments

Knobfin sculpins likely arrived accidentally in Connecticut in the early 2000s with a commercial shipment of live fish from the Ozark Region. They remained present at low levels for over 10 years, then rapidly proliferated and spread into all available main stem habitat. Historical fish sampling data show that impacts to other resident fish species, including young trout, have been devastating, and impacts to aquatic invertebrate species, such as crayfish and aquatic insects, are probably significant as well. Future efforts to contain the spread of this species will focus on outreach and education to deter private transfer to other streams.