Little monsters under the microscope: Parasites in our Largemouth Bass

“I have no idea what this thing is, some sort of a spiny-headed worm or something,” called out Michelle, a technician in the lab. Transfixed by the insidious creature, she zoomed in with the microscope to take a closer look as she described what she saw. “It looks something like a small leech, but instead of a sucker it has a hardened front end with recurved spines.” “Recurved spines?” I thought, sounds nasty! The little monster was a quarter of an inch long, but under the microscope it was clear that this animal meant business. It had clearly been shaped by evolution to do one thing very well: embed itself and never let go.

The thorny-headed worm, Acanthocephala, under our microscope. Recurved spines on the head (upper left side) enable it to remain lodged in the gastrointestinal lining of its host.

It was our first day looking through the stomach contents of young Largemouth Bass that we had captured this fall, and I was in the process of training each of the technicians on how to properly dissect the stomachs and identify their contents. I was used to seeing the normal diet items, such as zooplankton, aquatic invertebrates, and small fish, but I had never seen something like this! Continue reading


The night life

This fall, our field team is out conducting electrofishing surveys on sixteen lakes in Michigan (video). Our goal is to determine if changes to shoreline habitats are impacting the growth, reproduction, and population sizes of Largemouth Bass. When we catch Largemouth Bass, we also compare what they were eating to the habitats in which they were found. Almost halfway through our surveys for the year, we’ve collected plenty of data. Here are a few shots from the field.

Time lapse of electrofishing surveys conducted at Pine Lake, Michigan. Continue reading

Mapping Michigan’s lake habitats

Our main hypotheses are that habitats affect the distribution, abundance, diets, and growth rates of Largemouth Bass. How do we get this habitat data? In previous posts I’ve discussed how we catch fish and collect their gut contents, so this article will focus on our vegetation mapping.


We mapped patches of vegetation in lakes, such as these lily pads near a developed shoreline with its vegetation cleared.

Vegetation mapping techniques have advanced rapidly in the past decade with new technologies allowing us to do things that we never thought possible. Some of the first aquatic vegetation maps in Michigan were produced in the 1930’s and 1940’s, but required careful surveying and were limited in resolution. Computer programs now enable digital mapping, which in turn makes research such as ours possible. In a perfect world, we would simply use aerial or satellite photos taken around the same time as our surveys. These techniques have been used with some success on the Great Lakes, but their application to small inland lakes can be hampered by water clarity, tree canopy cover, and expense. The NASA option out, the next best plan was to visually map each lake in the field. Continue reading

Video from the Field: Largemouth Bass in our Net Pen Experiment

The summer is flying by, and we’re almost done with our experiment at Blue Lake. We’re testing our hypothesis that young Largemouth Bass grow faster in habitats with vegetation. Every month we place a new batch of fish in the nets and look for differences in growth rates, diet, and body condition. We’ve already finished our July and August time periods, and recently put the fish into the nets for September. The good news is that with the new turtle fences we’re getting good survival rates in our pens and will have plenty of data to analyze. Just before we netted the August fish I shot some video to better understand behavior of our bass. Check it out below! Continue reading

Guts! Finding out what Largemouth eat


A live Bullhead we found fighting for his life in the mouth of a Largemouth Bass.

What’s it eating? In the fishing world, whenever a fish is cleaned for the frying pan, inevitably the curious fisherman will take a few seconds to remove the stomach and see what the fish was eating. Minnows were dinner last night? Time to get out the Rapala. Damselflies and mayflies? Break out the flyrod tomorrow evening. In fisheries research, scientists are also interested in what the fish are eating to better understand their biology and the ecosystem in which they live. How can we see what they ate without dissecting them? We pump their stomachs! Continue reading

The night shift begins! Electrofishing 16 Michigan lakes

Our team has started conducting nighttime electrofishing surveys of 16 Michigan lakes, meaning long days and lots of excitement!

I mentioned in the previous post that our big research question is, “what habitats are best for Largemouth Bass?” We are using net pens to confine fish to particular habitats and follow their growth, but of course fish can swim from habitat to habitat in many lakes. So, we are complementing the net pen research with a study of Largemouth Bass populations across lakes that provide different habitats. Some lakes have lots of aquatic vegetation while others have only a few spots. How much is enough? How much is too much? These are questions that have been addressed in the fisheries research to some extent, but most studies are from southern lakes choked with vegetation. Not much use up in Michigan! So, we are setting out to study these questions by comparing the Largemouth populations of many lakes to maps of aquatic vegetation and other habitat characteristics.

That means we get to go out and catch thousands of fish. The best way to do that is electrofishing, which I’ve already written about here. Here’s what it looks like from my perspective on the boat.

Continue reading

Bass research continues at Blue Lake

Hayden (left), Amanda (center), and Ayman (right) with the day's catch: Largemouth Bass for our net pens.

Hayden (left), Amanda (center), and Ayman (right) with the day’s catch: Largemouth Bass for our net pens.

Our big research question is “what habitats do Largemouth Bass survive best in”, but breaking it down scientifically into testable hypotheses is really tough! One way to approach the question is by confining the fish to particular habitats and seeing how they do. Of course, there are some big assumptions confining mobile fish, but more on that later.

On July 2, we began our first experiment of this year. We placed 12 net pens in Blue Lake (near Fountain, MI) and stocked them each with baby Largemouth Bass. The net pens are 10 feet by 10 feet, with an open bottom. We put the pens in areas with 0%, 50%, and 100% vegetation coverage, to see whether the fish grow better or eat differently. Our results from last year suggested that bass in pens with no vegetation grew more slowly. However, we were challenged by a major issue: turtles! Continue reading