Round-bodied reef fish with big eyes are a favourite among divers, but the words “pufferfish” and “porcupinefish” are often used as though they describe exactly the same animal. They are related, and both can inflate, but they belong to different fish families and have useful features that help divers tell them apart. The easiest clue: obvious spines Porcupinefish usually have prominent spines covering the body. In many species those spines lie relatively flat when the fish is relaxed and become much more obvious when the animal inflates. Pufferfish generally lack the long, obvious spines associated with porcupinefish, although their skin can still have small prickles or texture. Why do these fish inflate? Inflation is a defence mechanism. By taking in water and increasing body size, the fish becomes harder for a predator to swallow. Porcupinefish also make their spines more formidable in the process. Divers should never try to trigger this behaviour. Chasing, touching or cornering a fish simply to watch it puff up creates unnecessary stress. Look at the face and body shape Both groups often have expressive-looking eyes and compact bodies, but porcupinefish commonly appear more elongated when relaxed, while many pufferfish have smoother body outlines. Exact identification requires more than one feature because several species occur across tropical Indo-Pacific reefs. What do they eat? Many porcupinefish use strong beak-like teeth to crush hard-shelled prey such as molluscs and crustaceans. Pufferfish diets vary by species and can include algae, invertebrates and other reef food. Their specialised teeth are one reason they are interesting to watch while foraging. Where might you see them around Koh Tao? These fish can turn up around reef, rubble and rocky habitats. Rather than promising a particular species at a particular site, treat sightings as part of the variety of local reef life. Phoenix Divers’ Koh Tao dive-site guide introduces the different environments visited around the island. How to get a better encounter Stay neutrally buoyant and approach slowly. Do not chase a fish into a hole or beneath coral. Never touch or deliberately cause inflation. Let the animal continue feeding or resting naturally. Use a camera only if you can maintain position without damaging the reef. Why identification is worth learning Marine-life identification becomes more rewarding when you stop looking only for “big things” and begin noticing behaviour and small differences. A porcupinefish feeding around rubble or a pufferfish resting beneath a ledge can be just as interesting as a larger animal when you know what you are seeing. See the reef rather than a checklist Certified divers can explore local habitats through Phoenix Divers’ fun diving in Koh Tao. For any wildlife encounter, the same rule applies: observe calmly, give the animal space and never change its behaviour simply to get a closer look.