CREATURE FEATURE – A Small and Mighty Fish

Known for their amazing resilience, mudminnows are one of the least sensitive of fish. They can live in creeks, ponds, swamps, marshes, and bogs; and they manage to survive in highly developed watersheds like the Rouge. Our local resident, the central mudminnow (Umbra limi), is one of three mudminnow species found in the US. Traditionally, the Central mudminnow’s range was comprised of a wide band down the middle of the country; but because these little fish are often used as bait (and therefore transported in live bait buckets), their range has been expanding to both the east and the west. (Please don’t transport live bait.)

From a purely scientific point of view, mudminnows are not actually minnows. True minnows are members of the carp family (Cyprinidae), while mudminnows are considered to be related to pike (Esocidae). And while the scientific community seems to debate over the proper classification of mudminnows (between the Umbridae and Esocidae fish families), most people see a rather plain, small, fish and just call it a minnow.

HABITAT & LIFE CYCLE

Mudminnows like shallow, swampy areas. They seek out quiet waters with abundant vegetation, and it appears they rely on the cover of that vegetation throughout their lifecycle. Breeding takes place in the spring; and the eggs, which are quite sticky, are deposited on plants. Both young fry and adult mudminnows are known to hide-out within the vegetation (or even burrowed into the substrate). There, they hide from predators while also lying-in wait for prey of their own. At only two to four inches in length, mudminnows feed heavily on aquatic macroinvertebrates and the occasional smaller fish. In turn, they are preyed upon by larger fish, shore birds (such as herons), bull frogs, and muskrats.

It seems that mudminnows were designed to survive whatever nature throws their way. They can tolerate waters that are quite warm and waters that are very cold. Some anecdotal writers claim mudminnows can even survive freezing solid and thawing though this has not been proven. However, it is known that mudminnows can manage in poor quality water that is murky, highly acidic, and very low in oxygen. They are even known to survive without water, enduring through droughts by burrowing into the mud. Yes, when nature turns harsh and other fish die off, the mudminnow lives to swim another day.

One key feature to mudminnow survival, is their specialized gas bladder. A gas bladder (a.k.a. swim bladder) is an air-filled, internal organ that allows a fish to adjust its buoyancy and maintain its depth position within the water. In general, fish that swim at the surface or midpoint of  water have gas bladders. Likewise, bottom dwelling fish generally do not have gas bladders. Such fish rest on the substrate between short bursts of swimming. Mudminnows are bottom dwellers by preference only. They have a gas bladder and are fully capable of swimming at the water’s surface. But even more importantly, mudminnows have a modified gas bladder that serves as a rudimentary lung. This specialized gas bladder effectively allows the mudminnow to breath air. So, whenever the mudminnow needs a bit more oxygen it can swim to the water’s surface, gulp some air, and absorb the needed oxygen through its gas bladder.

This ability to absorb oxygen from air allows the mudminnow to survive locations with poor water quality (and little dissolved oxygen) and to enjoy a significant advantage for surviving winter. During cold, winter months, dissolved oxygen levels under ice are gradually depleted. Most fish enter a semi-dormant state where metabolism and oxygen needs are greatly reduced. Survival then depends on fate – on whether the water thaws in time to bring more oxygen before the fish die. But for the mudminnow, with its ability to obtain supplemental oxygen through its gas bladder, winter is far less threatening. The mudminnow gulps air from the small air pockets trapped under the ice and absorbs the oxygen through its gas bladder. With the benefit of this extra oxygen, the mudminnow remains active during the cold months. It retains a sufficient metabolism level to digest food, actively forages throughout winter, and then swims happily into spring.

TAKE ACTION

Even though mudminnows are some of the least sensitive fish, they still require adequate habitat spaces – specifically swampy wetlands – for breeding and survival. Mudminnows may be resilient in the face of poor water quality, harsh temperatures, and droughts; but even they cannot survive against a bulldozer. Sadly, the on-going destruction of quiet wetlands is the greatest threat to survival of this species.

Each summer, FOTR surveys the watershed to document our local fish community and monitor the overall health of the river. This August, our regular survey team will, once again, visit sites throughout the area to find, sample and record the presence of our fishy friends. Findings from our annual survey (and other monitoring projects) help local governments, universities, and corporations make better land use and conservation choices.

In recent surveys, mudminnows have been found in the headwater areas of Western Wayne County and in Oakland County. Additionally, the presence of mudminnows have been noted along the river’s lower branch as far east as the City of Wayne. Please see our Fish Monitoring page for additional information on recent surveys.

Let us hope that this year’s survey also finds a great many mudminnows, and let us work together to protect the watery habitat of this small, but mighty, fish.

Main Photo Credit: Robert Muller – Central mudminnow (Umbra limi)