Pop quiz: Do you know what an Oncorhynchus mykiss is? How about a Salmo salar? No? Well, unless you’re an ichthyologist, don’t feel bad. The first one is the scientific name for rainbow trout. The other is an Atlantic salmon (and an ichthyologist is a fish scientist). They’re both in the same fish family – the salmonids – but some fish called “trout” aren’t technically trout and some fish called salmon aren’t technically salmon. 

So, how do you tell the difference between a trout and a salmon and how do you sort out who’s who? Beyond that, why does it matter? The answers to those questions and more are in the following article. Find out what the scientific difference is, what the difference is when fishing them, and how they’re different on the plate. 

Trout vs. Salmon Biology

You probably already know that there are several kinds of trout and several kinds of salmon. So, the trout vs. salmon question isn’t a one-to-one comparison. They’re all in the same family, some are just more closely related than others. Let’s break down the salmonid family tree.

Cutthroat trout, rainbow trout, and all of the salmon except for the Atlantic salmon are in the Pacific trouts and salmons family (called Oncorhynchus). The Atlantic salmon and the brown trout have their own family (called Salmo). The third family (called Salvelinus) consists of the brook, dolly varden, bull, and lake trout. 

Some of these fish look so similar that it’s hard to tell which is which without taking tissue samples to a lab. However, several good key differences work as an overall sorting strategy. They don’t work in every single instance, but for our purposes, they’re good enough. 

The first difference is their color patterns. Salmon have more patterning above the lateral line. Trout have more overall patterning. Salmon are more streamlined, have a concave tail shape, and their upper jaw doesn’t go past the eye. Trout have thicker bodies, a more rounded head, and more scales from their adipose fin to their lateral line. Another good bit of anatomy to look at is the anal fin. Trout have a dozen or fewer rays in this fin. Salmon have 13 or more rays. You can also tell by differences in the mouth.

Knowing the difference is important for three main reasons: it helps you identify the fish in the area and what lures they’ll go for, some of these fish are protected by law and you don’t want to get caught with the wrong ones, and knowing which is which is useful for population counts and restocking plans. 

Fishing: Trout vs. Salmon

The biggest difference between trout and salmon when it comes to fishing is where they live. Although salmon are often found in saltwater and trout in freshwater, this isn’t always the case, especially when spawning. Salmon famously return to their spawning grounds every year. They come in from the ocean and head upstream into freshwater rivers and streams. Rainbow trout spend the first part of their lives in freshwater. When they prepare to go into the ocean, they must go through a biological shift that enables them to handle saltwater conditions. After this change, they’re known as steelhead. 

Once a salmon has spawned, it dies. That means they only spawn once and usually don’t make it back to saltwater. Trout can spawn many times and don’t necessarily return to the saltwater environment afterward. Once they spawn, trout hang around longer before they transit to the ocean, so that they can get bigger before facing ocean predators. Trout don’t have to go into saltwater at all and can live their entire lives in either freshwater or saltwater. 

Trout and salmon each much the same food, so the bait and lures you choose can bring in either fish. Some behavioral differences will affect how you retrieve and where you cast. In lakes, you can catch trout using a worm suspended under a bobber. You can also fish trout by using some split shot to sink the line and allowing the bait to float a foot or two off the bottom. Spinners, spoons, and flies are effective lures. When fishing landlocked salmon in a lake, you can use the same bobber you would use for the trout. Suspend your bait about three to five feet from the bobber over a dropoff. Both fish will move lower in the water column as the weather cools down, so adjust your fishing depth accordingly.

For more on trout fishing, check out the Oregon Dept. of Fish and Wildlife.

For more on using the correct hook size for trout, read What is the Best Hook Size for Trout Fishing?

Cooking: Trout vs. Salmon

Both salmon and trout are good fish to eat. Some have a better flavor, depending on the species. Sockeye salmon is one of the most sought after fish for their rich flavor and high oil content. Chum salmon, however, does not come highly recommended. 

Nutritionally, they each have their benefits. Both have high levels of Omega-3 fatty acids. Salmon tends to have more fat, but less cholesterol. Trout has slightly fewer calories, protein, and saturated fat than the same amount of salmon, but not by much. Salmon is a good source of Vitamin D, while trout have strong concentrations of B vitamins. 

If you’re shopping, you’ll be more likely to find salmon cut into steaks and trout left whole. Filets of both are widely available. Trout are more apt to have a milder flavor that takes on herbs and spices better. Salmon are often described as having a sweet flavor.

That’s an overview of all things salmon and trout. Since so many fish fit into this family, it’s hard to make hard and fast rules that encompass them all. Some of the differences are so subtle that, outside of science, don’t matter much to your average angler. But no matter what you end up catching, don’t forget the number one rule of fishing – stay safe and have fun!