Finding fish with your fishfinder is one thing; differentiating between them is an entirely different task. Why should you care? Because it’s exceedingly difficult to pull a kingfish out of the school of fish you see on the LCD, if all the fish you’re looking at are menhaden. Sure, sometimes it’s easy to tell what’s what. Most folks know that when they see a big round blob on the screen, it’s baitfish. When they see a single strong arch, it’s a lone predator. But there are also some more subtle things to look for which will help you differentiate between species.
Big triangles, dead on bottom – These are black drum feeding on shellfish beds. Few species make such a distinct triangular return, connected to the bottom (as seen above). Any time you’re in an area black drum are found and this is what you see, get those baits ready fast.
Caterpillar-like wormy strings of fish, running just over the bottom – This is how a school of trout often shows up when you find them in relatively deep water. When the high pressure is hitting hard and the fish have lock-jaw, you’ll often see them form up like this in a hole, or along a deep edge. Catching them will be tough, but at least you’ll know just what you’re looking at and have an idea of how to target them.
Long, drawn-out arches – These are fast predators. You could be looking at kingfish or Spanish mackerel, and in offshore waters, this is also how wahoo show up. The give-away is the fact that the arch is long but not very deep, which means the fish is swimming quickly (or your boat is moving rapidly, though at high speeds, it’s not a great idea to put a ton of trust in your fishfinder in the first place).
Short, stubby, deep arches – Conversely, these are slow-moving fish. This is often how bass lounging in deep water appear on-screen, as well as fish like snappers or grouper that have come out of their hidey-holes.
Let’s note that none of the above applies to side-finders, which usually project fish as single dots or clusters of dots, as opposed to arches. Truth be told, it’s much harder to identify fish on a side-finder than a down-looker. One interesting note: the new 3-D system from Navico colorizes the returns from fish off to the sides, so they’re much easier to differentiate from clutter or other false returns.
Finally, let’s point out that the more you use your fishfinder and the more often you catch fish that you were recently looking at on-screen, the better you’ll become at ID-ing the blips and blobs. In other words, practice makes perfect—so you now have one more reason to get out there and go fishing more often.