I am bad at fish identification. There, I've said it. Even though my job title is "FISHeries Specialist", even though I have a Master's degree in FISHeries Science, even though I spent hours in Ichthyology lab studying preserved specimens, and probably inhaling a bit too much formaldehyde in the process, just put a bucket of fresh minnow-sized fish in front of me and I will forget everything I know, or so it seems. You could throw a few emerald shiners in there, and I did my THESIS on emerald shiners, and I would go crazy trying to separate them out from creek chubs, fathead minnows, common shiners, Johnny darters, and stonerollers. And please, don't even get me started on dace. Northern redbelly dace, finescale dace, pearl dace. They all look the same to me. At first.
I've been doing some fish sampling by electrofishing on a small river in east central Minnesota. The river is quite small and the water level low; it was completely dry in some parts. The equipment we use is a backpack shocker powered by a generator. Basically, one person wears the unit and controls the anode, which is on a long pole. The other person (or two people) carry dip nets and buckets to hold the fish. When the unit is running, the electric field around the anode causes fish to involuntarily swim towards the anode (Galvanotaxis--word of the day). The fish are temporarily stunned, but the voltage is not high enough to kill most fish instantly. Kind of a fun way to go fishing, if not the most sporting.
At the end of the sampling station, it's time to sort through the catch, and then the fun begins. I dip a net full of slimy, wiggling fish and look at each one, separating them into smaller buckets by species. Some fish are obvious: the eel-like burbot, brook stickleback, and central mudminnow are unmistakable. Darters, members of the perch family, are a little tricky but still have some distinctive characteristics for each species. But once you get into the Cyprinidae (minnows), all distinctions start to blur. It takes some kind of mental adjustment to start paying attention to smaller, less obvious details. Are the scales large, or small? What is the shape and relative size, even the angle, of the mouth? Is the body more flattened or cylindrical? What is the relative size of the eye?
Another confession: I hate dichotomous keys. For those of you who do not know what a dichotomous key is, it's a guide to fish (or any organism, plant or animal) identification that goes through a series of questions based on physical characteristics to progressively narrow down the possibilities until you run out of choices. In theory it is foolproof; at each level, a fish is either this or that, black or white, scaled or scaleless. But then, especially with cyprinids, they start throwing in criteria like lateral line scale count, dorsal fin rays, mouth angle, and pharyngeal teeth counts. When you're looking at a bucket of hundreds of individuals, you don't want to be counting tiny scales on each one. And the keys often contain ambiguous phrases like "mouth more or less subterminal"...what's this more or less business? Or my favorite: One choice says 10-15 dorsal fin rays, the other says 12-17 dorsal fin rays. So what do you do if your specimen has 14 dorsal fin rays? Give me a good illustrated guide any day; I'm not anal retentive enough to go through the steps to "key out" specimens.
Okay, nerdy biologist rant over. When all is said and done, I'm amazed at the diversity of life that is present in even the tiniest stream. The fish life alone is impressive; we're finding fifteen or more different species at each sampling spot. And even the small fish are beautiful; the striking colors of the redbelly dace (though they are not always brightly colored), the intricate markings of the Johnny darter, the iridescence of the bluntnose minnow (today's species that had me baffled for way too long), the young-of-year smallmouth bass. I even shocked an eighteen inch northern pike that was hiding in a weed bed in less than a foot of water (We measured and released that one quickly). It's all out there; how few people ever take the time to discover it!