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Fish Identification – Beyond Fish-in-Hand and the ID Guide

By Sean Mitchell

There you are, early morning of a beautiful summer day, retrieving the minnow traps and fyke nets you set out the previous afternoon. This is always an exciting moment; you never know what you might find strayed into your traps through the night. Gently transferring the catch into a bucket you begin to dip out individual fish to identify. This should be the easy part, right? But wait, what is that? You have not seen that fish before. And it kind of looks like a golden shiner, but not quite right. Confused you reach for the field guide in your backpack.

Identification of freshwater fish in Canada is challenging. Many people assume it is simple and straightforward, or worse, that is it easy and they have it mastered; but it is a skill requiring continual practice and honing. Many species look very similar (particularly among the minnows), there is geographic variability among individuals of species leading to differences in appearance among streams, colours change with age and spawning condition, and then there are the hybrids to complicate things.

Of course your most valuable tool is a good regional guide to the fish species present in your area. But, in addition to using dichotomous keys, flowcharts, or FOPLAP (flip open page, look at pictures), I present here a few other considerations I have learned from a few decades of this. These are tips to help guide you in what to look for or what to do when you, in exasperation, have to toss the guide aside and say “I do not know”.


Tip 1: Know the expected species in your area of interest. Before going to sample a stream or lake, do your homework. What species are known in the drainage? Take a list of those species with you. Effectively you have shrunk your candidate list from all fish in the province or region to a much smaller list of those actually known in the waterbody. Then, if you think you have a species in your captures that has not been recorded before in the watershed, you may want to reconsider your identification. At least you recognize it as potentially very important and so worthy of confirmation of your identification (Tip 7).

Resources for determining species present in river systems may be traditional books (though dated, Scott and Crossman1 remains excellent for across the country) or online databases. Most provinces have some form of publication on fish distribution within their boundaries; some of these are better than others. The online databases tend to be more current, but be aware that these often have limited to no quality control and so misidentification is, unfortunately, very common. The number of times I see slimy sculpin listed as present in BC coastal streams is astonishing (this species does not occur that far west – I think people just like the name and immediately jump to that species).

Tip 2: Know the piscine species-at-risk and invasive species in your area. These are identifications you do not want to get wrong as they have management consequences. If you are going to report presence of a threatened or non-native species you want to be sure you are correct. If you suspect a species-at-risk, document carefully (Tip 7); if non-native or invasive, consider collecting as a voucher specimen (Tip 8).

Tip 3: Consider habitat: did you pull the fish out of a large pool or a riffle? Are you in the headwaters of a stream or the lower reaches of a river? High-gradient cascade pool versus flat glide? Different species prefer different habitats — knowledge of this can help us narrow down our identification.

Tip 4: Use morphological features and patterns for identification, not colour. Colour is highly variable both geographically and in response to water clarity: waterbodies of tannic water often have darker toned fish than clear water ponds. Colour also can change dramatically through the year as spawning versus non-spawning dress. Instead, focus on features such as number of fins, locations of fins relative to each other, length of mouth, pattern of lateral line, presence and size of parr marks, etc. These do not change among populations.

Tip 5: Don’t guess. When you don’t know, say you don’t know. Take it to family or genus level if that is all you can do with confidence. Better to have you tell me you caught a lamprey sp. rather than a western brook lamprey incorrectly identified. I have horror stories of projects with wasted money and effort, as well as damaged credibility, as the field crew identified the majority of captured fish as species not occurring in the region. They misidentified all of their fish, but they did so with great confidence. Don’t guess, just identify to the level that you have reasonable certainty.

Tip 6: To really learn the identifying features of your local fish, create your own identification key. Start with just a single group, such as a small family (e.g., the sculpins, the lampreys, the basses and sunfishes…). Develop you own personalized flow chart on discriminating between the species. Avoid tackling a massive and confusing group such as the salmonids or cyprinids — these are intimidating and very complex groups; leave these until you have gained some confidence. The act of creating your own key moves you from a passive learner looking at pictures and reading other’s text, to determining for yourself those features that separate the different genera or species. This is the most powerful exercise you can do to learn your fish.

When you cannot identify with confidence,

Tip 7: Photograph the fish and consult with experienced colleagues. Include something for scale in the photograph (a ruler, a dime, an object of known size). Capture multiple images from different angles to account for lighting and reflections interfering with clear photos. This is best done with anaesthetized fish so it is not moving. Photograph the head in close-up to the best of your ability; do the same for the body. Submit the photos to a trusted and knowledgeable colleague. It is critical that we remember that sometimes the most truthful and powerful thing we can say is: “I don’t know”.

Tip 8: If identification is imperative, and it is not a species-at-risk, collect a voucher specimen for analysis by experienced people. A voucher specimen is one or a small number of individuals killed for the express purpose of identification and long-term archiving. The process of preserving fish for voucher specimens is too detailed to get into here but guidance may be found in RIC (1997).2

Fish identification is, of course, principally done in the field with fish in-hand. But, knowing how to short-list your unidentified species to a group of candidate species and what to do in the event you cannot identify with great certainty, is also part of the identification process. While I cannot tell you how to identify each individual fish species in Canada within the confines of a blog, these eight tips will serve you well to help figure out that problematic piscine critter in your hand.

NRTG is developing an on-line fish identification course for roll-out in autumn, 2021. Initially we will focus on fishes of western Canada but then customize for other jurisdictions.

2 Resources Inventory Committee. 1997. Fish Collection Method and Standards. Version 4. Province of British Columbia. Ministry of Environment, Lands and Parks.