Oklahoma's number one blog for natural and cultural history.
It’s slimy. It’s creepy. It’s just in time for Halloween. This week we’re diving down into a world unseen, to the murky and mysterious dwelling of Oklahoma’s more aquatic residents. We’re not talking catfish and bass, here. Oh no. We’ve got something far more exotic in mind, something coiled in chills and thrills. Brace yourself for the American eel.
An American eel specimen from our ichthyology department
Although the American eel, Anguilla rostrata, is a widespread and common fish species of the Atlantic and Gulf drainages of North, Central and northern South America, it is currently rare in Oklahoma. Eels are catadromous fishes, meaning they spend part of their life cycle in the ocean and the other part in freshwater. American eels spawn in the ocean. The larval eels drift in currents to the mouths of large freshwater rivers where they migrate upstream to feed in freshwaters before returning to the ocean as adults to carry on the circle of life.
Due to their poor eyesight, eels most likely depend on their sense of smell to find prey. American eels are nocturnal and therefore do the bulk of hunting at night. Unlike other fish, the American eel’s scales do not overlap in an organized pattern, but rather occur irregularly across the body. Despite these minute scales, the American eel appears to be “naked” because of a mucous layer that coats the body.
A mucous coating creates a slimy look
Although American eels are currently rare in the state, as mentioned above, they were once fairly common in the large rivers of Oklahoma, particularly in the eastern part of the state. However, the construction of impoundments has hindered their migration. As a result, their population has been declining in Oklahoma since this specimen was collected from the Kiamichi River in southeastern Oklahoma in 1973, and prior to this photograph, had not been opened since that date.
The Kiamichi River, photo courtesy of www.oklahomaroadtrips.com
They were once fairly common in the large rivers of Oklahoma, particularly in the eastern part of the state, but the construction of impoundments has hindered their migration. As a result, their population has been declining in Oklahoma since this specimen was collected from the Kiamichi River in southeastern Oklahoma in 1973, and prior to this photograph, had not been opened since that date.
Dr. Marsh-Matthews, ichthyology curator, uncoils the eel for a close-up
The American eel certainly isn’t our most adorable specimen, but there’s just something compelling about that creepy-but-cool stare. Next week we’ll be trading the slime and scales for feathers and flight, so don’t miss out. Now that you’ve had a chance to see the American eel in all its glory, we have a question for you: chilling or thrilling? Join the conversation on our Facebook page!
A red shiner minnow.
Now you see them; now you don’t. After years of being the most common fish in local creeks, the red shiner seemingly disappeared from several streams in southern Oklahoma.
Dr. Edie Marsh-Matthews, an ichthyologist at the Sam Noble Museum, and her colleagues have been studying the fish community of Brier Creek in southern Oklahoma for many years. In 2005, they noticed that red shiner minnows had disappeared from many creeks where they had once been very common, including Brier Creek. All of the creeks from which red shiners disappeared are direct tributaries of Lake Texoma, a manmade impoundment of the Red River and Washita River in southern Oklahoma.
The loss of the red shiner was very puzzling because it is very common and tolerant of extreme conditions, such as high temperature and low oxygen in the water. To explain the loss of this hardy fish, Dr. Marsh-Matthews and her colleagues suggested that the creeks might have been altered over time due to the reservoir in a way that increased habitats for predators on red shiners. Then, in 2007, there was a major flood during which lake waters backed up many miles into the creeks, and red shiners reappeared in some of the creeks. The scientists expected that the red shiners would once more become common in Brier Creek, but surprisingly, they were not.
Dr. Marsh-Matthews and her student at Brier Creek.
To try and understand the reasons that red shiners could not become re-established in Brier Creek, Dr. Marsh-Matthews and her colleagues designed a series of experiments using the artificial streams located at the University of Oklahoma’s Aquatic Research Facility.
Artificial streams are used to replicate natural environments.
A peek inside the observation window.
By producing artificial environments similar to those of Brier Creek, Dr. Marsh-Matthews could control variables while closely monitoring changes in the red shiner population. After conducting several rounds of experiments, she and her colleagues found a possible explanation why red shiners may not be able to re-establish in Brier Creek. In their experiments, sunfish predators lowered survival and reproduction of red shiners. Scientists had discovered that the number of sunfish has increased in Brier Creek over time.
“So, we think that these predators are not only involved in the initial loss of red shiners but also as they became more abundant in these altered streams, but maybe they’re not letting them come back,” Dr. Marsh-Matthews said.
Dr. Marsh-Matthews introducing red shiners to the artificial stream.
These studies on the red shiner disappearance and failure to re-establish in Brier Creek can have importance for many stream ecosystems. Although the red shiner is a native species in Oklahoma, what we learn about its ability to re-invade its native habitat will contribute to invasion biology, the study of factors that affect the establishment of species outside their native range.