Amblyopsis rosae
Ozark Cavefish
(Also: Ozark cavefish)

With the only recorded populations in the world found in seven adjacent counties in the midwestern United States, Amblyopsis rosae is truly a locally endemic species. The only three states that contain counties with the cavern environment necessary to sustain their delicate niche are in Arkansas (Benton County), Missouri (Barry, Greene, Jasper, Lawrence, Newton, Spring, and Stone Counties), and Oklahoma (Delaware and Ottawa Counties). Due to decades of both natural and human-related pressures, historical populations of A. rosae have experienced a reduction in their range, which may still be occurring today. The common name, Ozark cavefish, is derived from the Ozark Highlands, a large plateau spanning three states. In states where they are found, populations have been verified in at least 21 different cave localities. (Noltie and Wicks, 2001; Romero, 1998)

Ozark cavefish are extremely specialized to their cave ecosystem, requiring a pristine water source that remains at a temperature between 12.8 and 15.6°C. Because of this, they typically occupy caves whose water source comes from swelling groundwater, as opposed to surface-running streams. Access to this groundwater is possible due to the geologic characteristics of the plateau under which they live. Lying under a layer of exposed rock and soil, various types of eroded limestone including Burlington, Pierson, and Keokuk, make up the walls of individual cave habitats. Beneath this layer of limestone lies a bed of Chattanooga shale, which the groundwater settles on, allowing the groundwater to swell into the caves. In addition to the natural purification of the groundwater, the physical isolation of the cavern environment keeps out competing organisms and/or pathogens that are more prevalent in surface stream environments.

Because of lack of sunlight, streams in these caves are relatively barren, with mainly rocky, small-pebbled bottoms. Species richness is low, limited to a few species of salamanders, invertebrates, and copepods. (Culver and Pipan, 2009; Graening and Brown, 2003; Noltie and Wicks, 2001; Willis and Brown, 1985)

With an average length of approximately 38 mm and mass of approximately 2.5 g, Amblyopsis rosae has evolved into a species that lacks pigmentation. Their de-pigmented epithelial layer is absent of melanin, thus they have a translucent appearance. As a result, the visceral organs can often be seen through the fish, consequently giving it a pinkish tint. Ozark cavefish lack a pelvic fin as well as functional eyes. This lack of sight is a result of the environment, which has rendered sight useless in the dark depths of caverns. To compensate for the absence of vision, A. rosae has a nervous system that is highly sensitive to smell and sound. (Noltie and Wicks, 2001; Poulson, 1963; Romero and Conner, 2007; Romero, 1998)

The Ozark cavefish life cycle begins as an egg that is held within the gill chambers of the female. For four to five months after hatching, the young remain within the confines of the gill chambers. By doing this, young fry have the opportunity to grow and, upon leaving the gill chamber, are less likely to be victims of cannibalism. Maturation through their intermediate stages is very slow; both sexes grow an average of 0.6 mm per month. Regardless of age, individuals that are smaller in size tend to grow at faster rates compared to those of larger size. (Noltie and Wicks, 2001; Poulson and White, 1969; Poulson, 1963; Poulson, 2001)

Ozark cavefish are polygynandrous species, mating at random with multiple partners in an attempt to increase population fitness, although not all females may have ova ready for fertilization. (Noltie and Wicks, 2001; Poulson, 1963; Romero, 2001)

Ozark cavefish are considered sexually mature at age 4. Regardless of their sexual maturity, about 20% of the mature female population develop ova each year. It is believed that this reproductive limitation results from limited food sources in the cave. This birth limitation also helps to control food availability; lower population sizes do not demand as much food, which is limited in the cave environment. Eggs produced during each breeding period tend to be large in size and low in number when compared to similar species. (Poulson, 1963; Romero, 1998; Romero, 2001)

Though juvenile Ozark cavefish are independent, parental investment before and after hatching is high. Once the eggs fertilized, they are transferred to the female's gill chamber, where they remain for four to five months until hatching. During that time, the female is responsible for protecting the eggs from harm. This, in turn, temporarily reduces her fitness as she is unable to be as mobile as she would be without her offspring. Males provide no parental investment outside of fertilizing the female ovum. (Poulson, 1963; Romero, 1998; Romero, 2001)

Ozark cavefish grow at a slow rate, approximately 0.6 millimeters every month, and have a long lifespan. Because they are only viable in the wild and conservation measures restrict the capture of this species, a measure of average lifespan in captivity is not available. However, the average lifespan of wild populations is approximately 10 years. (Poulson, 1963)

Ozark cavefish have an extremely low metabolism. They spend the majority of their time hovering motionless in stream waters. Ozark cavefish exhibit aggressive behavior when provoked. However, they are relatively sedentary, conserving energy in their resource poor environment. (Graening, et al., 2009; Noltie and Wicks, 2001; Poulson, 1963; Romero, 1998)

Home range size in Ozark cavefish is not described.

Because populations of Ozark cavefish are small and individuals are relatively solitary, communication with individuals outside of mating is limited. However, perception is vital for this species, as they have no vision. Ozark cavefish rely on concentrated bundles of nerves in their peripheral nervous system known as neuromasts. These neuromasts, located on the caudal fin, are able to detect motion in the surrounding water in the form of ripples or waves. They also have a lateral line across the side of their body which is far more sensitive than that of other fish species. Through a function known as hydrodynamic imaging, Ozark cavefish are able use this sensitive lateral line to create a picture of their surrounding environment. (Noltie and Wicks, 2001; Romero, 1998; Romero, 2001)

Ozark cavefish are carnivorous. The diet is relatively specialized, as prey choice is limited to the few organisms that are found in their cave environments. Ozark cavefish consume crayfish species including cave crayfish and spot handed crayfish; eggs from darksided salamander and cave salamanders; stygobitic arthropod species such as Stygobromus onondagaensis and Stygobromus ozarkensis; as well as a species of styobitic isopod. Additionally, they are cannibalistic. A portion of the diet, during periods of hatching, may consist of newly hatched young and/or developing juvenile cavefish. (Graening and Brown, 2003)

Ozark cavefish do not have any natural predators. Most deaths are due to dying from old age or from cannibalism in younger stages. Humans harm Ozark cavefish populations as a result of disruption from cave spelunking or collection of specimens for research. (Brown and Johnson, 2001; Graening and Brown, 2003; Poulson, 1963; Poulson, 2001)

Cave streams inhabited by Ozark cavefish are nutrient-poor because of their isolation from natural nutrient inputs, such as decomposing materials that make up the base of the food chain, including rotting leaves, soil, and dead organisms. The primary input of decomposing organic matter in these cave streams is guano from gray bat (Myotis grisescens) roosts. (Cambray, 2000; Graening and Brown, 2003; Poulson, 2001)

Ozark cavefish are often targeted for academic research because of their unique ecology, evolution, and their endangered status. This research has the potential to generate positive economic roles in the form of research grant money. (Graening, et al., 2009; Stephens and Horton, 2007)

Ozark cavefish do not negatively effect humans in general, although protection efforts can disrupt certain cave sports. A handful caves in Missouri, Oklahoma, and Arkansas have been quarantined in an attempt to help preserve the species. (Brown and Johnson, 2001; Graening, et al., 2009; Stephens and Horton, 2007)

Both the United States Federal List and the International Union for Conservation of Nature's Red List indicate that Amblyopsis rosae is a threatened species. The primary threat is pollution of cave stream habitats. Habitat disturbance is also a major threat; both through over-collection of A. rosae specimens and caving and spelunking. Also, declining groundwater levels are negatively affecting populations.

To combat these effects on the Ozark cavefish, the states in which they are found have taken measures to ensure their conservation, such as blocking off the entrances to caverns. Additional monitoring techniques are also being practiced, such as water quality and population monitoring. (Brown and Johnson, 2001; Cambray, 2000; Graening, et al., 2009; Romero, 1998; Stephens and Horton, 2007)

Historically, Ozark cavefish have acted as biological indicators. Early settlers of the Ozark plateau would search for Ozark cavefish in the buckets of water they drew from their wells. Because they are extremely sensitive to water quality, only surviving in pristine waters, settlers would know that the drawn well water was clean and safe enough to consume if they found an Ozark cavefish. This important role gave A. rosae the title of "well keepers" or "spring keepers." (Graening, et al., 2009)