Cottus undescribed species

[Espinasa, Smith and Lindquist 2021]



Espinasa and Jeffery (2003) recorded a troglomorphic fish population from a cave in Pennsylvania, USA. They do not differentiate it taxonomically from epigean fishes in the Cottus bairdi-cognatus complex. The following details refer only to the troglomorphic fishes.


Cottus bairdii-cognatus complex  [Espinasa and Jeffery 2003]

The fish is known by the common name of Nippenose Cave Sculpin.




Since the troglomorphic population has not been considered as a separate taxon there are no designated types. Espinasa and Jeffery (2003) do not record any museum reference numbers (but see below).


Type locality: Eiswert #1 Cave, Nippenose Valley, Lycoming County, Pennsyvania, USA (41o9’23.2”N, 77o12’21.1W). Known also from Loose Tooth Cave, Nippenose Valley, Lycoming County, Pennsylvania 41o8’18.4”N 77o13’32.0”W (Espinasa, Cahill, McCaffery and Millar 2013) 223masl. This is the second most northerly of all subterranean fishes after Barbatula undescribed species from Germany (47o50’48.48”N, 8o51’28.91”E). Cottus bairdii from further south in Pennsylvania (40o36’04”N, 78o13’01”W) is the third.


Eiswert #1 Cave is a small vadose stream segment between a sink and a rising. It is likely that the hydrological connection between the downstream end of the cave and the rising is passable to fishes moving up and down stream. There is therefore potentially some degree of connection between epigean and hypogean populations.


The taxonomic position of the troglomorphic taxon is not clear. Two species from which it may be derived, Cottus bairdi and C. cognatus, together with hybrids between the two, are found in the vicinity of Eiswert #1 Cave. The diagnostic characters used to separate these species (3 pelvic fin rays in C. cognatus, 4 pelvic rays in C. bairdi and hybrids) is difficult to apply as fin ray reduction may be a troglomorphic character. It is likely that molecular techniques will be required to resolve this question. Cahill et al. (2013) suggest that the hybridization event between C. bairdii and C. cognatus generated an adaptationally distinct lineage which was able to evolve into a troglomorphic population. Cottus bairdii from Tytoona Cave (the Tytoona Cave Sculpin), which is only slightly troglomorphic, is in the same lineage as the surface fishes in the area and no hybridization event took place there.

Biological Notes

Espinasa and Jeffery (2003) consider these fishes as troglomorphic as follows: "The characters normally used in recognizing troglomorphic fish, blindness and depigmentation, are not fully developed in this population. Nonetheless, these fish have a suite of modifications that readily identify them as cave-adapted: Elongated pectoral fins, more numerous and enlarged cephalic lateralis pores, a broader head, increased subdermal fat reserves, and in the brain, size reduction of the tectum opticum."

Conservation Status


Luis Espinasa reports (pers. comm.) that a large pig farm is to be built on the karst surface directly above Eiswert #1 Cave. This would certainly be detrimental to the fishes in the cave. It is encouraging that Espinasa and Jeffery (2003) explicitly cover conservation status in their account of this species. They rightly consider that this population should be protected under the United States Endangered Species Act.

Museum Holdings

Espinasa and Jeffery (2003) report that all specimens examined in the course of their study are deposited in the Pennsylvania State University fish collection.

Key References

Stone, R.W. Journal Article 1953 Caves of Pennsylvania
Robins, C.R. Thesis 1954 A taxonomic revision of the Cottus bairdi and Cottus carolinae species group in eastern North American (Pisces, Cottidae)
Williams, J. D. and Howell, W. M. Journal Article 1979 An albino sculpin from a cave in the New River drainage of West Virginia (Pisces: Cottidae)
Troester, J.W. and White, W.B. Journal Article 1984 Seasonal fluctuations in the carbon dioxide partial pressure in a cave atmosphere
Strauss, R.E. Journal Article 1986 Natural hybrids of the freshwater sculpins Cottus bairdi and Cottus cognatus (Pisces: Cottidae): Electrophoretic and morphometric evidence
Jones, W.R. and Jannsen, J. Journal Article 1992 Lateral line development and feeding behaviour in the mottled sculpin, Cottus bairdi (Scorpaeniformes, Cottidae)
Coombs, S. Journal Article 1999 Signal detection theory, lateral‐line excitation patterns and prey capture behaviour of mottled sculpin
Coombs, S., Finneran, J.J. and Conley, R.A. Journal Article 2000 Hydrodynamic image formation by the peripheral lateral line system of the Lake Michigan mottled sculpin, Cottus bairdi.
Brison, L.L. Thesis 2001 Experimental analysis of metabolic adaptation of Cottus carolinae in response to photoperiod and food availability
Coombs, S., Braun, C.B. and Donovan, B. Journal Article 2001 The orienting response of Lake Michigan mottled sculpin is mediated by canal neuromasts.
Kanter, M.J. and Coombs, S. Journal Article 2003 Rheotaxis and prey detection in uniform currents by Lake Michigan mottled sculpin (Cottus bairdi)
Espinasa, L. and Jeffery, W.R. Journal Article 2003 A troglomorphic sculpin (Pisces: Cottidae) population: Geography, morphology and conservation status
Robins, C.R. Journal Article 2005 Cottus kanawhae, a new cottid fish from the New River System of Virginia and West Virginia
Espinasa, L., Cahill, A., McCaffery, S. and Millar, C. Journal Article 2013 Partial sequence of a gene involved in skin colouration (MC1R) from the Pennsylvanian Grotto Sculpin
Espinasa, L., Mendyk, A., Schaffer, E. and Cahill, A. Journal Article 2013 The Second Northernmost Cave-adapted Fish in the World? Groundwork on the Tytoona Cave Sculpin Population
Cahill, A., Yurgel, M. and Espinasa, L. Conference Paper 2013 Hybridization and the colonisation of the cave environment by fish
McCaffery, S., Collins, E. and Espinasa, L. Journal Article 2014 Eye histology of the Tytoona Cave Sculpin: Eye loss evolves slower than enhancement of mandibular pores in cavefish?
Fernholz, J. and Phelps, Q.E. Journal Article 2016 Influence of PIT tags on growth and survival of Banded Sculpin (Cottus carolinae): Implications for endangered Grotto Sculpin (Cottus specus)
Fernholz, J. Thesis 2017 Influence of PIT tags on growth and survival of Banded Sculpin (Cottus carolinae): Implications for endangered Grotto Sculpin (Cottus specus)
Ruppert, J.L.W., James, P.M.A., Taylor, E.B., Rudlofsem, T., Veillard, M., Davis, C.S., Watkinson, D. and Poesch, M.S. Journal Article 2017 Riverscape genetic structure of a threatened and dispersal limited freshwater species, the Rocky Mountain Sculpin (Cottus sp.)
Gebhard, A.E and Perkin, J.S. Journal Article 2017 Assessing riverscape-scale variation in fish life history using banded sculpin (Cottus carolinae)
Fernholz, J. Thesis 2018 Influence of Pit Tags on growth and survival of Banded Sculpin (Cottus carolinae): Implications for endangered Grotto Sculpin (Cottus Specus).
Baek, S.Y., Kang, J.H., Jo, S.H., Jang, J.E., Byeon, S.Y., Wang, J.H., Lee, H.G., Choi, J.K. and Lee, H.J. Journal Article 2018 Contrasting life histories contribute to divergent patterns of genetic diversity and population connectivity in freshwater sculpin fishes
Espinasa, L., Smith, D.M. and Lindquist, J.M. Journal Article 2021 The Pennsylvania grotto sculpin: population genetics