Jars of pickled fish specimens on a shelf

Research Story: Digging Deeper into the Mysteries of One of Minnesota’s Rare fish

Published10/18/2021 , by Tyler Muller

In the muddy Mississippi River backwaters in southeast Minnesota lies one of Minnesota’s weirdest fish, the pirate perch (Aphredoderus sayanus). This fish isn’t a true perch however, instead it predates modern perch and only bears a superficial resemblance. Pirate perch are specialized nocturnal predators spending most of the day wedged deep in submerged roots along stream banks only emerging enough to defecate from their cloaca, which has migrated towards their throat, before retreating into structure to avoid the larger toothy predators lurking in the same waters.

With help from the Bell Museum’s curator of fishes, Dr. Andrew Simons, I will look at population expansion, evolution, and taxonomy of this state-listed species. While these fish are rare in Minnesota, they become more common in the Southern portions of their range. These fish are ubiquitous in the lowland Mississippi River drainages from Illinois south to the freshwater bayous and swamps that eventually drain into the Gulf of Mexico. In the tea-colored blackwater rivers that characterize the Atlantic slope between Georgia and New York, pirate perch look noticeably different from their Mississippian counterparts which has led to some taxonomic confusion.

A small brownish colored fish

Pirate Perch, Aphredoderus sayanus

 

This species has gone through a handful of taxonomic changes. Pirate perch were first put into the same genus as an unrelated marine fish from the Indo-Pacific in the early 1800s, followed by taxonomic lumping and splitting as ichthyologists debated whether this was a single species, multiple species, or subspecies. The most recent comprehensive study of the pirate perch morphology argues that they are two subspecies with a large intergrade zone in Mississippi, Alabama, Georgia, and Florida where hybridized populations cannot be distinguished.

My approach to answering these questions is to sequence DNA from these fish throughout their geographic range to understand if they are a single species and to estimate when these fish expanded north up the Mississippi river and the Atlantic coast. With these DNA sequences, I can also determine how related each of these populations are, better delineate species/population boundaries and determine whether these northern populations are relict populations from a larger historic range or new colonizers expanding northwards. This data can shed light on the origins of Minnesota’s fish fauna and determine if humans caused a reduction in populations, or if Minnesota is a new frontier for southern species as global temperatures rise. Unlike traditional morphological studies which can be satisfied with pickled specimens from natural history collections, this DNA-based study will require fresh tissue samples from live fish and a lengthy collecting trip.

My collecting started in Reno Bottoms, a series of Mississippi River sloughs and backwaters near the Iowa and Wisconsin borders. This was not an easy place to sample, as the sediment was ankle to thigh deep and any movement would turn the water chocolate milk brown. After a couple of miles of wading through this swampy refuge, we came across a single specimen. Though follow-up trips to the driftless area were unsuccessful, I pushed ahead on a planned month-long 20 state collecting trip following the range of these fish where I would collect populations from 12 states. Aside from camping amenities and non-perishable snacks, I set out with whatever fish sampling equipment I could find in my advisor’s lab, gallons of ethanol and formaldehyde for preserving fish and tissue samples, a mini-roadside genetics toolkit, and two totes full of empty bottles to be filled with new fish for the Bell Museum fish collection.

A bayou in Louisiana. Overgrown trees stretch over murky water

Bayou at the Dewey Wills Wildlife Management Area in Louisiana.

On my first stop in Illinois, I met with an old colleague and a newly hired biologist from the Illinois Natural History Survey. A few days later in Texas, I was able to recruit three young men from Texas Tech University who just finished their own aquatic survey to help me collect fish. On my second to last day, in Delaware, an ambitious first-year professor from Salisbury University and his friend made the short drive from Maryland to assist. For the remaining fifty or so sites, I waded into the lowland streams, bayous, and Cypress swamps solo to explore these untouched habitats and search out Pirate Perch among an ever-changing mixture of regionally adapted fish species.

A group of researchers in a swamp

Photo courtesy of Hayden Hays, L-R: Aaron Gunnar Gray, Tyler Muller, Kort Alexander. Shocking a small spring feeding into Big Cypress Bayou in Texas.

 

After several hundred pirate perch, thousands of miles, and a heart still racing from a month of non-stop action, I sit back down in the lab with DNA extraction reagents in hand and can begin the next step towards unraveling the mysteries of this quirky fish.