A Starter Guide to Indonesian Reef Fish ID

One of the best things about snorkeling is the endless sense of discovery. Just when you think you’ve seen it all, you come across a fish that’s been there all along, you just never noticed it until today. Then, suddenly, you start spotting it on every snorkel. Fish identification is never ending! And if you ever feel like the more you snorkel, the less you know, don’t be discouraged. Fish are the most diverse group of vertebrates on the planet, so there’s always a new name to learn. To help sharpen your fish ID skills, I’m going to introduce you to the four most common families of Indonesian reef fish, explain how to identify them, and sprinkle in a few fun fish facts along the way, because who doesn’t love those?

Damselfish

On my most recent tour, I had the pleasure of introducing a guest to the damselfish family. Once you start noticing them, it’s mind-boggling just how many different species there are. In fact, one could argue that without damselfish, the reef would lose a lot of its sparkle. Damselfish are often called the “confetti fish” because they burst out from coral heads like fish-fetti! If approached, they seem to move as one, ducking back into the coral for shelter in a perfectly synchronized flash. These coordinated movements are like underwater fireworks and will leave you mesmerized.

If you’ve ever snorkeled over a tropical reef, I can almost guarantee you’ve seen a damselfish. They are one of the most common reef fish and can be identified by their oval-shaped, laterally flattened bodies, forked tails, and are almost always found in groups. Most damselfish are between 2 and 15 cm long, although some species can grow up to 30 cm. Color isn’t the best way to identify them, as they come in every color in and out of the rainbow. Instead, look for their body shape and behavior. One of the most commonly seen damselfish is the blue-green chromis (Chromis viridis). These dazzling, electric blue-green fish hover in large groups above branching corals in the shallow reefs. Other common species in the damsel family, are sergeant majors and all anemone fish including the famous clown fish. 

If you get caught up watching their hypnotic movements and drift a little too close, don’t be surprised if a tiny damselfish suddenly darts straight at your mask! It’s their way of telling you that you’ve entered their territory, and despite their small size, they’ll do their very best to scare you away. Damselfish are also surprisingly noisy. They communicate by making pops, clicks, and crackling sounds, using them to defend their territory and interact with one another.

Perhaps the coolest behavior of all is that some species are underwater gardeners. They carefully cultivate patches of algae by removing unwanted species and encouraging the growth of the ones they prefer to eat. As if tending to their garden, they graze, weed and fiercely protect their algae farm from invaders.

Wrasse 

Okay, so wrasse are a tricky one. I like to say, “If in doubt, it’s probably a wrasse” These fish come in an huge variety of shapes, sizes, and colors, from the tiny cleaner wrasse to the giant Napoleon wrasse. With over 600 known species, they are one of the most diverse families of reef fish around.

Fortunately, there are a few simple clues that can help you identify them. Unlike many fish that propel themselves by sweeping their whole body from side to side, wrasse do most of their swimming with their pectoral fins (the fins on either side of their body). They “row” through the water with these fins, only using their tail for quick bursts of speed when they need to make a fast getaway. Another telltale feature is their long, continuous dorsal fin, which runs almost the entire length of their back, from just behind the head to the base of the tail. Once you learn to spot these characteristics, you’ll be surprised by just how many wrasse you start noticing on your snorkels.

A very fascinating wrasse fact is that most species are protogynous, meaning they’re all born female and as they mature, some undergo hormonal changes that transform them into males. One of the most dramatic examples is the humphead Napoleon wrasse. As a female changes into a male, she undergoes an incredible transformation. The fish grows much larger, develops the iconic hump on its forehead which he uses to battle other males and win the attention of the females. 

Butterflyfish 

Butterflyfish are probably one of the easiest reef fish families to identify because, unlike many others, their color and body shape are actually reliable clues. Most species are a combination of yellow, white, and black, with a distinctive black band running through the eye. This clever marking helps disguise the location of their eye, making it more difficult for predators to target them. Many species also have a dark spot on the rear of their body that acts as a false eye, confusing predators about which direction they’re swimming.

Butterflyfish are typically round bodied and laterally flattened, with a pointed snout perfectly adapted for sucking up coral polyps and other small invertebrates from the reef.

One of the fun things about butterflyfish is that you can often guess their name from their markings. Take my favorite, the teardrop butterflyfish, which has a distinctive teardrop-shaped marking on its side. Or the pyramid butterflyfish, which you’ll often see gliding over Indonesian reefs in schools of hundreds. Whichever of the more than 50 species you encounter in Indonesia, butterflyfish are guaranteed to be among the most elegant and eye-catching fish on the reef.

What makes these fish even more lovable is that they mate for life. If you watch them as they swim across the reef, you’ll notice they work as a team. While one fish lowers its guard to feed on coral polyps, the other stays alert, keeping watch for potential predators. Then they swap roles, working as a team, taking turns to feed and stand watch. How adorable! 

Parrotfish

Parrotfish are a trademark fish of tropical reefs, easily recognized by their bright blue colors and distinctive beak-like mouths with white teeth. However, there are many species of parrotfish, and they are not always brightly colored. In fact, 39 species are found on Indonesian reefs, all playing an important role in reef health.

Most parrotfish are herbivores, feeding on algae that grows across the reef. This is vital for reef health. As they scrape away algae, they expose clean rock where new coral larvae can settle and grow. Without this grazing, reefs would quickly become dominated by algae instead of coral. Thank you, parrotfish!

Color alone is not a reliable way to identify them, as juveniles and females are often dull brown or red, while males are often multicolored and vibrant. Instead, look for their beak-like mouths and their swimming style, like wrasse, they use their pectoral fins in a flying motion to swim. If you hear scraping sounds while snorkeling, a parrotfish is likely nearby feeding.

One of the most impressive species is the humphead parrotfish, often seen in groups munching their way across the reef. Once you spot them, it wont be for long as they often disappear behind a cloud of sandy poop. This sand is produced as they grind up limestone while feeding on algae and excrete it. A single humphead parrotfish can produce up to 200 pounds of sand per year!

Final Thoughts

When identifying fish, focus on shape, size, and behavior rather than color, as many species change color throughout their lives and even throughout a singe day. After learning your damselfish, wrasse, butterflyfish and parrotfish, look out for surgeonfish, groupers, and gobies too!