Unlock the Secrets of Fish Identification – Part 5: Color

There are a lot of "red fish" in the sea

Whether you're snorkeling in the shallows or diving into the deep blue, identifying fish can feel like trying to solve a beautiful underwater puzzle. In this fifth installment of our Fish ID series, we're diving into one of the flashiest clues nature gives us: color! But beware – things aren't always as they seem beneath the waves.

More red fish

🌈 Color – The Ocean’s Optical Illusion

At first glance, a fish’s color might seem like an obvious identifier – bright yellow, deep blue, fire-engine red. But color plays tricks on us underwater. As you descend deeper than 33 feet, red disappears into the shadows. That "bright red squirrelfish"? Below that depth, it can look grey or even black. Why? Because red light wavelengths are absorbed quickly in water. So, while color is incredibly helpful for fish ID, it's not always reliable on its own – especially the deeper you go.

The depths that different colors start to fade in the ocean. (Adapted from NOAA Ocean Exploration)

Even more red fish (the first 5 fish are all in the seabass family)

You’ll quickly notice there are a lot of “red fish” out there – squirrelfish, soldierfish, cardinalfish, seabass, and more. But here's the catch: while they may all appear similar in color at the surface or in photos, they often look completely different underwater, especially at depth. Once you’re below 33 feet, red wavelengths fade fast, turning those vibrant hues into dull greys or blacks. And on overcast or cloudy days, this color loss happens even sooner, making it even trickier to rely on color alone. That’s where the true keys to fish identification come in: shape, behavior, and habitat. For instance, a cardinalfish and a squirrelfish might both be “red fish,” but their dorsal fins have very different shapes. When in doubt, look at the whole picture – not just the color.

The body shape of a squirrelfish

The body shape of a cardinalfish

Squirrelfish Cardinalfish

Juvenile vs. Adult: Same Fish, Different Look

Another layer of complexity in fish identification is that many species change color dramatically as they grow. A perfect example is the blue tang – a familiar sight to many snorkelers in the Virgin Islands. As juveniles, blue tangs are a bright, solid yellow with a hint of blue around the edges, but as they mature, their color shifts dramatically to blue. Spotting one at different life stages could easily make you think you’re seeing two entirely different species.

Juvenile blue tang

Adult blue tang

Juvenile blue tang Adult blue tang

In both life phases the shape and behavior are the same, but the color changed wildly, you might have thought they were two different species!

🧩 Cracking the Code: Family First

When you're trying to ID a fish, it’s best to start broad. This is where shape, behavior, and general pattern come in.

• Shape is your first big clue. Is the fish long and torpedo-shaped like a barracuda? Flattened like a flounder? Tall and thin like an angelfish?

• Behavior is next. Is it sitting motionless near coral (hello, scorpionfish)? Darting in and out of rocks (a typical damselfish move)? Schooling in open water (could be bar jacks)?

• Habitat is next in importance. Does the fish live in the seagrass flats, the mangroves, the coral reef, or all of the above?

These broader traits help narrow down the family the fish belongs to – kind of like saying, “This fish is probably a parrotfish, not a damselfish.”

🎯 Then, Dial in the Details: Species

Once you’ve narrowed it down to a family, that’s where pattern, color, and size step in to help you zero in on the species.

• Pattern refers to more permanent traits like stripes, spots, or bars. These are more consistent across family lines and can often survive even if the color fades at depth.

• Color can distinguish between closely related species – but remember the depth trick. A red fish at the surface might look black at 60 feet.

• Size helps too. Most fish start life hatching from small eggs, but few fish grow to sizes larger than 3-4ft.

It’s like narrowing down a suspect list. First, you identify the general look and behavior. Then, you use the fine details – a stripe, bar, or spot – to make the final call.

🧠 Color Takeaways for Smart Spotters

• Use shape, behavior, and habitat first to place the fish in a family.

• Then use color, pattern, and size to zero in on the species.

• Remember that color fades with depth – especially red!

• Fish can change color due to mood, mating, or camouflage – another reason not to rely on color alone.

📸 Pro Tip: Use a Dive Light or Flash

Want to see a fish’s “true colors”? Bring a dive light! Artificial light brings back the reds and oranges lost in deeper water and helps you capture better photos for later identification.

Fish identification is part science, part art, and all adventure. So next time you're exploring the reef, remember: don't just look at color – look at the whole fish. With a bit of practice and curiosity, you'll be unlocking the underwater mysteries like a pro.

Ready to test your fish-spotting skills?

A fairy basslet

I’d love to hear about your own fish identification experiences! Drop a comment below and share what fish you've spotted or any tips you've picked up along the way.

To help you along your fish ID journey, some great resources are the app Fishes: Greater Caribbean by D. Ross Robertson and James Van Tassell and the ID books Reef Fish Identification Florida, Caribbean, Bahamas by Paul Humann and Ned DeLoach and Caribbean Reef Life – A Field Guide for Divers by Mickey Charteris

📸 All photos courtesy of Sara and Lee Richter 📸