Eye Picking and Pebble Picking Behaviors of Cutlip Minnow, by Don Orth

Cutlip Minnow Exoglossum maxillingua is no ordinary minnow.  Two behaviors make it quite unique -- nest building and eye picking. Compared to other minnows, its movements are sluggish, staying near the bottom of clear, rocky streams. But during the spring breeding season, males become hard-working nest builders, selecting pebbles and bringing them to the nest site at a rate up to 6-10 per minute.  This eventually results in a pebble mound that can be 12 to 18 inches across and 5 to 6 inches high.   Wow!  Just consider the energy expended by nest building and tending – a 6-inch Cutlip Minnow can barely transfer a ¾ inch pebble.  Females are smaller and do not participate in the nest building.  The male stays at the nest day and night until breeding has ceased (Hankinson 1922; van Duzer 1939). 

Cutlip Minnow.  Photo by Matt Tillet

The distribution of the Cutlip Minnow ranges from Virginia to New York in streams of the mountains and piedmont provinces.   Here, the Cutlip Minnow co-occurs with many other fishes, including the Common Shiner Luxilus cornutus, Creek Chub Semotilus atromaculatus, Rosyface Shiner Notropis rubellus,  Tesselated Darter Etheostoma olmstedi, White Sucker Catostomus commersoni, and Blacknose Dace Rhinichthys atratulus.   Common Shiner and Rosyface Shiner breed on the nests built by Cutlip Minnows and their constant swimming and darting is in contrast to the behavior of the Cutlip Minnow (van Duzer 1939; Maraukis et al. 1991).  

Distribution of the Cutlip Minnow from NatureServe.

The eye-picking behavior of the Cutlip Minnows has frustrated many field biologists when collecting these fishes.  All types of fishes collected are typically placed in a large bucket until enough are collected to identify and count them all.  Collected fishes held in the bucket with the Cutlip Minnows often have missing or damaged eyes.  Antonios Pappantoniou and George Dale  (1986) discovered that the Cutlip Minnow would immediately pick at the eyes of a goldfish added to an aquarium with many Cutlip minnows.   Furthermore, the Cutlip Minnows were not fooled by the camouflage of  false eyespots or eye lines on fishes (Dale and Pappantoniou 1986).  When in crowded situations, the Cutlip Minnows like fish eyes!

Close-up, ventral view of the mouth of the Cutlip Minnow.  Photo by Brian Zimmerman.

The mouth of the Cutlip Minnow is unique in that the lower jaw consists of a central bony plate flanked by two fleshy lobes.  Only one other fish, the Tonguetied Minnow Exoglossum laurae, has this unique mouth morphology   The ventral mouth would seem to be specialized adaptation for benthic feeding on snails, insect larvae, and diatoms.  Eye-picking does not appear to be an adaptation for feeding on the eyes of other fishes.  The mouth morphology also facilitates the transport of pebbles of a particular size as seen in other nest building cyprinids (Bolton et al. 2015).

In a recent study, Bramburger et al. (2018) observed that nests of Cutlip Minnow were composed of mainly dark pigmented pebbles.  They speculated that the colorful, dark pebble might enhance mate selection by female Cutlip Minnows. Male Cutlip Minnows get darker during breeding but they do not possess secondary sexual characteristics that would serve as cues for sexual selection.   However, Bramburger et al. discovered that the substrate from nests were significantly darker and more saturated than random samples of stream substrata.  No other examples of nest substratum color selectivity has been reported in fishes.  At this stage, all one can do is speculate.   Perhaps darker substrate absorbs/conducts more heat energy (Brown 1969; Johnson 2004) that speeds embryo development.

Our not so ordinary little minnow may possess secrets that are yet to be explained.  

References

Bolton, C., B.K. Peoples, and E.A. Frimpong. 2015. Recognizing gape limitation and interannual variability in bluehead chub nesting microhabitat use in a small Virginia stream. Journal of Freshwater Ecology 30: 503-511.  

Bramburger, A. J., K.E. Moir, and M.B.C. Hickey. 2018. Preferential incorporation of dark, coloured materials into nests by a mound-nesting stream cyprinid. Journal of Fish Biology

Brown, G. W. 1969. Predicting temperatures of small streams. Water Resources Research 5:68-75. 

Dale, G. and A. Pappantoniou. 1986.  Eye picking behavior of the cutlips minnow, Exoglossum maxillingua:  Applications to studies of eye spot mimicry.  Annals of the New York Academy of Science 463:177-178.

Hankinson, T.L. 1922.  Nest of cut-lips minnow, Exoglossum maxillingua (LeSueur). Copeia 102:1-3.

Johnson, S. L. 2004. Factors influencing stream temperatures in small streams: substrate effects and a shading experiment. Canadian Journal of Fisheries and Aquatic Sciences 61(6):913-923.

Maurakis, E.G., W.S. Woolcott, and M.H. Sabaj. 1991. Reproductive behavior of Exoglossum species. Bulletin of the Alabama Museum of Natural History 10:11-16.

Pappantoniou, A., and G. Dale.  1986.  Eye-picking behavior of the cutlips minnow Exoglossum maxillingua: density relationships.   Annals of the New York Academy of Sciences. 463:206-208.

van Duzer, E.M. (1939) Observations on the Breeding Habits of the Cut-Lips Minnow, Exoglossum maxillingua. Copeia  1939:65-75.  

Investigating The Obscure Yeller Finned Minner, by Don Orth

Let’s call it the Clinch Dace.  It’s a small minnow, which the locals call “yeller finned minners.”  When Freshwater Fishes of Virginia was first published in 1994, this minnow was not known, at least to scientists.   It’s referred to as Chrosomus sp. cf. saylori.   This means we are sure it is a member of the genus Chrosomus, the fine-scale daces.  The sp. is an abbreviation for species, meaning we are not sure what the species really is.   The cf. is an abbreviation for the Latin verb conferre.   This tells one to consult with or compare with the species saylori, because it is most similar to the Laurel Dace Chrosomus saylori.  The Laurel Dace was described by Dr. Christopher Skelton (2001) and was listed as endangered by the U.S. Fish and Wildlife Service in 2011.  The Clinch Dace was encountered in surveys associated with gas pipeline planning and construction.  The fish was considered a unique species due to differences in morphological and meristic traits (White and Orth 2013).  Because it has not yet been described as a species it has no federal protection. In Virginia, it is a Tier I species (very high conservation need) in the Virginia Wildlife Action Plan.

 

A,  Laurel Dace Chrosomus saylori Photo by Chris Skelton, B. Clinch Dace Chrosomus sp. cf. saylori Photo by Dave Neely

Michael J. Moore recently defended his master’s research which focused on this species. The thesis “Distribution and Population Characterization of Clinch Dace (Chrosomus sp. cf. saylori) in the Upper Clinch River System, Virginia” confirms the rarity and isolation of this fish within its putative range.  Clinch Dace occurred at only 13 of 70 sites sampled (18.6%).   The occupied sites were in small streams of low gradient and low conductivity in watersheds that were largely  (>80%) forested.  They rarely occurred with sculpin (Cottus spp.), but usually coexisted with Blacknose Dace, Creek Chub, Stoneroller, and Fantail Darter.  Both backpack electrofishing and minnow trapping were deemed to be feasible methods for capture and long-term monitoring. Although the Clinch Dace was found at two new locations, it was absent from two locations that previously had Clinch Dace.   The species occurs at low densities, in only 31.5 of the 351 km of headwater streams, making the global population size quite low (below 7,000 adults).  

Dashed line shows range of all collections of Clinch Dace.

Coal mining, logging, gas wells, cattle pastures, roads and culverts occur throughout the highly dissected landscape where the Clinch Dace may be found.  Here, the impacts of surface mining outweigh current mitigation actions, which have been largely criticized (Bernhardt et al. 2012).  The surface mine impacts can have long-lasting and significant effects on aquatic life.  For example, one isolated population of Clinch Dace exists upstream from a large surface mine in Left Fork Coal Creek (see photo).  Here the conductivity is less than 200 μS/cm.   However, downstream of the discharge from the surface mine, conductivity values increase to over 1,000 μS/cm.  Different ionic constituents are part of the dissolved solids loading, though these are not regulated. Of further concern, is that the community of Fork Ridge, Virginia, is one of 50 communities at highest risk of mountaintop mining. 

Aerial photo of Fork Ridge surface mine and isolated Clinch Dace habitat. Photo by D.J. Orth

The landscapes where the Clinch Dace reside provide a microcosm of what is occurring throughout the coal-mining region of Appalachia.  Coal is removed by a method known as contour highwall mining or mountaintop removal and valleys are filled with mine spoil.  Drainage from these surface mines and valley fills have high levels of dissolved solids, which remain elevated for long distances downstream and for 2 decades or more after the mine is “reclaimed”  (Evans et al. 2014). Aquatic macroinvertebrate communities are impaired by high ionic concentrations; these same small creatures are part of the food base for many fishes, including the Clinch Dace. It is unlikely that eggs and larvae can survive the elevated ionic concentrations.  Others have also detected a conductivity threshold for stream fishes. A threshold of conductivity likely exists, above which Clinch Dace and other fishes cannot persist.   With the small, and isolated pattern of the Clinch Dace populations, any further losses in habitat are troublesome.  At present, four of the largest populations in the least disturbed watersheds are the hope for the future of the species. 

We still need to quantify the levels of genetic diversity remaining in these small populations. Habitats that are important for Clinch Dace spawning  need to be identified and protected.  With cooperative landowners we need to identify and remove barriers to population expansion and monitor responses.  These yeller finned minners belong in the small streams that drain these hollers.  There are no alternative habitats once a valley is filled in.   

Landscape in the region occupied by Clinch Dace. Photo by D.J. Orth.

References

Bernhardt, E.S., et al. 2012.  How many mountains can we mine? Assessing the regional degradation of central Appalachian rivers by surface coal mining. Environmental Science and Technology 46(15):8115-8122.

Evans, D.M., C.E. Zipper, P.F. Donovan, and W.L. Daniels. 2014.  Long-term trends of specific conductance in waters discharged by coal-mine valley fills in central Appalachia, USA.  Journal of the American Water Resources Association  50(6):1449-1460.

Skelton, C.E. 2001.  New dace of the genus Phoxinus (Cyprinidae: Cypriniformes) from the Tennessee River drainage, Tennessee. Copeia 2001:118-128.   

White, S.L, and D.J. Orth. 2013. Ontogenetic and comparative morphology of Clinch Dace (Chrosomus sp. cf. saylori).  Copeia 2013(4):750-756.