When you picture a landlocked salmon and then a brown trout, I’m sure the two species are clearly distinguishable. In certain Maine water bodies both species are present and on occasion the two species can be tough to quickly identify. Which, to be fair, is not that much of a surprise. Landlocked salmon and brown trout are closely related (both falling under the genus; Salmo) which lends the two species to look similar in some circumstances. In general, these fish are easy to identify with even novice anglers being able to note the clear differences between the two.
If you find yourself with a fish in question, there are certain morphological differences that should key you into what species you have caught, and yes, the vomerine teeth are a clue.
1. Know the species present in the water you are fishing
First things first, you should be aware of what species are present in the lake you are fishing. This seems like a simple concept, but in many cases, you can eliminate one species or the other just based on what species are known to be present in the water body. Check the recent stocking report to see which species has been stocked or view a historical lake survey map. There are lakes and ponds that are stocked with both species, and the regulations could be different for the two, so this makes it very important to be able to properly ID the fish.
2. Look at the Vomerine teeth
If you are questioning your catch on whether you are holding a salmon or brown trout, we can first start with the vomerine teeth. This is probably the most talked about identification factor. Vomerine teeth are the teeth located on the roof of the mouth on both species. Salmon have a single row of small teeth on the shaft with little to none on the vomerine head, while brown trout have a prominent zig-zagged row of teeth on the shaft and well-developed teeth on the vomerine head. (Tip: to remember this, just remember salmon=single).
Unfortunately, looking for the vomerine teeth won’t give you an ID 100% of the time. In older, larger fish, both species can lose these teeth. Although salmon have smaller less developed vomerine teeth that can be prone to loss, brown trout can also lose teeth especially if they get to the age of five or older.
3. Tails tell
I like to start at the caudal fin (or tail) and then the caudal peduncle. Salmon will have a slightly forked caudal fin, while brown trout will have a square tail with almost no fork. The caudal peduncle is the area on the fish to which the caudal fin or tail is attached. The caudal peduncle on salmon will be “thinner” but tends to be thick on the brown trout. These features can be clear and are a great place to start.
4. Look at the adipose fin and upper jaw
Moving up toward the head, I also like to look at the adipose fin. Brown trout tend to have larger adipose fins and will often have an orange tint and often have obvious spots. Salmon will usually have a dark adipose fin and if the fin has spots, it will be harder to see. I then go to the mouth of the fish. The maxillary process is the part of the fish’s upper jaw that extends down toward the lower jaw. The maxillary on salmon typically will not extend much past the eye, but brown trout often have a maxillary that slightly extends past the eye. Usually this is a good indicator and is better observed when the fish’s mouth is closed (and observed best in pictures taken with little to no angle).
5. Colors and spots vary
There are a few other indications that can point you in the direction of a correct ID. The general coloring of both species can vary. Both species can be very silver, golden, or just a mix of both. Some coloring can be more obvious than others, but generally if a fish is really golden, it can be obvious that the fish is a brown trout. Just a general idea on how salmon and brown trout typically look will give you a good start, but don’t let that persuade you if it’s not obvious. Typically anglers will confuse large male fish, as well as fish that are dark in color with golden hues. Post-spawn male landlocked salmon can be dark and golden and look a lot like brown trout (you may catch post-spawn salmon during the late fall or ice fishing season).
Of course, every fish is different, and some things can be more obvious than others, and even environmental factors can be an influence on how the fish look. No different from the general coloring of the two species, typical spotting patterns can be another good clue and something to look out for, but not solely relied on. Brown trout usually have more spots than salmon and tend to have a few more reddish spots. Most commonly, salmon will have smaller less defined spots compared to those of the brown trout. When you identify multiple features (like coloring and spotting), the correct species starts to become clear, but there are always exceptions to the rules.
If you just aren’t sure, it’s always safe to release the fish. No harm, no foul if the fish returns to the water. You can’t replace experience, and even though most cases are straight forward, putting all these tips together should help with the occasional fish that may need some extra attention to correctly identify. Hopefully these steps and tips will settle a few debates between you and your fishing buddies this year.
Originally published in the MDIFW blog on Jan. 19, 2023.
