Grotto Sculpin

Cottus specus

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Grotto sculpin side view photo with black background
Grotto sculpin, Cottus specus
Lance Merry
Endangered
Species of Conservation Concern
Family

Cottidae (sculpins) in the order Scorpaeniformes (mail-cheeked fishes)

Description

The grotto sculpin, which occurs only in Perry County, Missouri, looks much like the closely related banded sculpin, but it has smaller eyes, a paler body, and other features fitting it for cave life. The overall color is light tan to bleached tan, with underparts unpigmented.

Sculpins, as a group, have very large mouths. The head is broad and flattened, tapering abruptly into the rather slender body. Scales are absent, but small prickles are often present on the head and body. The dorsal fin is divided into two distinct parts; the forward part contains spines, but these are soft and flexible, superficially resembling soft rays. The pectoral fins are large and fan-shaped. The pelvic fins each contain 1 stiff spine and 3 or 4 soft rays. The rear margin of the tail fin is rounded.

The grotto sculpin can be distinguished from other Missouri sculpins by the following:

  • The lateral line is complete, ending near the base of the tail fin.
  • Marks are similar to the closely related banded sculpin, with a dark vertical bar crossing the body at the base of the tail fin broad and distinct, but the overall coloration is paler.
  • Unlike the banded sculpin, the eyes are smaller.
  • It only occurs in certain caves in Perry County, Missouri.

Similar species: Five species of sculpins occur in Missouri.

  • Until 2013, the grotto sculpin was considered an unusual form of banded sculpin (C. carolinae), but DNA evidence showed it was different enough to be considered a separate species. The description above clarifies how to tell them apart.
  • The Ozark sculpin (C. hypselurus), knobfin sculpin (C. immaculatus), and mottled sculpin (C. bairdii) also occur in clear, rocky, spring-fed Ozark streams. Where they occur, they may have higher population densities than the banded sculpin. They have varied distributions in different Ozark stream systems, and they can be distinguished from each other through differences in coloration and markings, fin ray counts, and other fairly subtle differences, including molecular (DNA) traits. They all differ from the banded sculpin in having an incomplete lateral line (ending beneath the base of the soft dorsal) and in having the dark vertical bar at the base of the tail fin narrow and indistinct.
Size

Adult length: commonly 2½–4 inches.

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Grotto sculpin female, side view photo with black background
Grotto Sculpin Female
Grotto sculpin, Cottus specus, female

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A grotto sculpin on the stream floor. Its has large oval pectoral fins.
Grotto Sculpin
Grotto sculpin are adapted for cave life. The overall color is light tan to bleached tan, with underparts unpigmented.

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Photo of two grotto sculpin.
Two Grotto Sculpin
Grotto sculpin live in and around 6 cave systems in Perry County. Adult length is between 2½ and 4 inches.

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Illustration of a grotto sculpin, side view.
Grotto Sculpin (Side View)
The grotto sculpin is a unique, cave-dwelling species closely related to the banded sculpin. Grotto sculpin are found only in Perry County, Missouri.

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Illustration of Grotto and Banded Sculpins.
Grotto and Banded Sculpins
The grotto sculpin (left) is a cave-dwelling close relative of the banded sculpin (right).

FG-0042_Sculpin_Grotto.mp4

Video of grotto sculpin in the wild.
Habitat and conservation

Sculpins, as a group, are bottom-dwelling fishes that lack a swim bladder. Their flattened bodies and enlarged pectoral fins are adaptations for maintaining a position in stream currents. They are able to modify their color to match their background and are difficult to see as they lie on the stream bottom.

Grotto sculpins live in and around 5 caves and one stream in Perry County. Like their more pigmented relatives, they are bottom-dwellers, but they are specially adapted for life in caves.

Land use around sinkholes has a profound impact on ground water quality and sculpin health. Sinkholes supply water to cave streams and groundwater sources. This makes sinkhole pollution control imperative. Establishing a buffer of trees and other plants around sinkholes reduces soil erosion and filters out herbicide and pesticide runoff.

Other conservation efforts include protecting a cave's recharge area (the area of land through which water moves into springs or caves), minimizing disturbance to cave wildlife, and protecting cave entrances.

For a single cave system, the recharge area can be many miles wide. Pollutants, such as agricultural chemicals and animal waste, roadway runoff, leaking septic tanks, contaminants from trash thrown into sinkholes, and even excess silt from a variety of construction and agricultural earthworks, can seep into the groundwater, polluting caves, springs, and well water.

Foods

Sculpins as a group have very large mouths and are able to swallow prey items nearly as large as themselves. In cave systems and their spring openings, the grotto sculpin’s food includes cave isopods and amphipods, crayfish and many other bug-like creatures, as well as small fish (including other sculpins).

image of Grotto Sculpin Distribution Map
Distribution in Missouri

Occurs only in certain caves in tributaries of the Bois Brule River drainage in Perry County, in southeast Missouri.

Status

A Federal Endangered Species found only in a single area in Missouri. In 2013, genetic testing determined that the grotto sculpin was different enough from the banded sculpin to deserve its own scientific name. It is a rare fish with a very limited distribution, meaning it is very vulnerable to extinction. Because the water in their caves comes from sinkholes and through porous rocks above, land use easily impacts their water quality.

The new species name, "specus," refers to its cave habitat.

Life cycle

Biologists are still learning about the life cycle of this species. Mating occurs in spring. The male cleans and excavates a nest under a rock, then courts the female. Eggs are deposited on the underside of the rock. The male guards the eggs until they hatch. A recent study suggests that young grotto sculpins often spend their first season at “resurgence sites” outside of the caves, in order to grow more quickly before reentering the caves, where larger sculpins might otherwise eat them.

Human connections

The grotto sculpin is valuable as an environmental indicator. Its presence indicates that the caves it inhabits have clean water. As long as grotto sculpins thrive, southeast Missourians can rest assured that groundwater supplies in the area are healthy.

Human wealth takes many forms, in addition to the common sense of “money.” That Missouri — the Cave State — is blessed with such interesting subterranean features and an abundance of fascinating, rare, and elegant creatures, makes us rich beyond description.

Aquatic caves — ones with permanent or nearly permanent water — are fascinating, unique, and fragile. Humans have only a limited understanding of aquatic cave species and their interconnections.

Ecosystem connections

Caves have their own suite of predators and prey species, and grotto sculpins are predators in these pitch-dark streams, swallowing insects, smaller fish, and crustacean-like creatures.

There are many other remarkable animals that are so specialized for living in caves that they cannot survive outside the cave environment. These include cave crayfishes, the Ozark, southern, and spring cavefishes, the grotto salamander, and several species of flatworms, cave snails, arachnids, amphipods, copepods, isopods, millipedes, insects, and more.

Because they cannot live without a cave habitat, and because a population is limited to its single cave system, one single pollution event affecting the groundwater seeping into the cave can potentially wipe out the entire population.