Mudminnows are small (80 – 200 cm) fish that are most closely related to pike and pickerel. Photo of Olympic mudminnow (N. hubbsi) courtesy of Roger Tabor, USFWS.

If ever a group of fishes were in need of a PR makeover, it’s mudminnows. Everything about the name – from undesirable mud to inconsequential minnow says “nothing to see here”. But these unassuming species are veritable Clark Kents of the fish world: small size and mild appearance disguise super-fish able to withstand dangerously low oxygen levels and defend spawning territories equivalent (if they were human) to two football fields. These are a few of the biodiversity secrets brought to light in a recent lab paper that reviews the distributions, biology, life-history, and conservation status of the five species of mudminnow distributed around the Northern hemisphere.

As a group, mudminnows are remarkable in their ability to thrive in harsh conditions. Eastern mudminnow (Umbra pygmea), native to the East Coast of the United States, not only tolerates but actually thrives in low pH levels that are lethal to most other fish. Blackfish (an Alaskan mudminnow species, Dallia pectoralis) are so cold tolerant that they were reputed by Native Alaskans to withstand freezing. Four of the five mudminnow species have adapted to breathe supplemental air through their swim bladder or esophagus, and Central mudminnow (Umbra limi) have been shown to “sip” air bubbles underwater when oxygen is low.


Mudminnow are found in shallow and densely vegetated habitats which are prone to warming, freezing, and dramatic changes in dissolved oxygen. Photo: L. Kuehne

The innovative adaptations of mudminnow are likely due to their favored habitat of shallow and densely vegetated swamps, ponds, and bogs. These areas can be harsh: subject to warming in summer, ice in winter, and extreme variations in oxygen availability and pH levels. These specialized freshwater habitats are also often small and vulnerable to human activities like draining of wetlands, water regulation, and pollution.

The review article came to be when we started a project studying Olympic Mudminnow (Novumbra hubbsi), which is highly endemic and found only in Washington State – by far the smallest range of any species. We found that much of the information about their ecology was piecemeal and anecdotal, with only nine peer-reviewed studies (several devoted to phylogeny). In this way, Olympic mudminnow share the plight of many noncommercial freshwater species, where research interest is difficult to come by and research funding even harder. This can make conservation status very difficult to assess.

Turning to other mudminnow species for answers, we found the same story: much of the literature was decades old and few of the articles longer than 2-3 pages. Answers to simple questions like “How old does an Alaska Blackfish get?” or “How many eggs do European Mudminnow produce?” were often best guesses, based on the results of small studies conducted in a local pond or stream. So a major focus of the review was to bring together results from numerous smaller studies to answer basic questions of ecology and life-history as well as identify information that was lacking for different species.

By synthesizing information across species we were able to illustrate why two species (European mudminnow and Olympic mudminnow) warrant conservation concern, and outlined the major threats to populations. Because mudminnow are not very mobile, a primary threat is water regulation which reduces or alters mudminnow habitat. Interactions with non-native species and pollution are also indicated as having negative impacts on populations, but could bear more investigation. By identifying research gaps for each species, we were also able to make focused recommendations for future research.

As I put together this review, I came to appreciate not only the diversity of mudminnow, but also what they represent in a world where freshwater environments (lakes, rivers, and wetlands) are disappearing and changing at an alarming rate. This small tribe of five species scattered around the Northern Hemisphere offers a fascinating snapshot into life-history diversity as well as unique adaptations to extreme and harsh environments. Mudminnow are an important reminder that we really have no idea what other super-fishes may be lurking in hidden pockets of the world, and suggest we should scratch the surface a little more before these areas become even more altered, threatened and endangered.

Lauren Kuehne

*The cover photo of Olympic mudminnow (Novumbra hubbsi) was taken by Roger Tabor, USFWS