The Black-Spotted Porcupinefish (Diodon hystrix) also known as Spot-fin porcupinefish is one of many fascinating species within the Porcupinefish family and is closely related to, but distinct from, Pufferfish. Porcupinefish belong to the family Diodontidae, while Pufferfish are part of the family Tetraodontidae. The main difference is that Porcupinefish have specialized scales that turn into spines when they puff up in defense, whereas Pufferfish do not have these spines.
Distinguishing Features
The Black-Spotted Porcupinefish is a medium-sized fish that can grow up to 90 cm, though it’s usually around 40 cm. It has an elongated body, round head, big eyes, and a large, often open mouth. It has large pectoral fins, no pelvic fins, and its anal and dorsal fins are close to the tail. These fins move together when swimming. Its smooth, firm skin has scales that turn into spines. The fish is beige to sandy-yellow with black spots on its body and fins.
Behavior and Movement Patterns
Black-Spotted Porcupinefish are usually seen alone but can be found in pairs or groups during mating. By day, they often hide in small reef crevices and may inflate to fit tightly. Sometimes, they rest on the bottom in the open, and they usually ignore divers, moving away only if approached too closely. They swim slowly using their pectoral, dorsal, and anal fins but can make quick bursts of speed with their tail fin.
Defensive Behavior
Like all pufferfish, Black-Spotted Porcupinefish can inflate themselves by swallowing large amounts of water. This makes them bigger and harder for predators to eat, and their spines stick out, making them look less tasty. They also have a special relationship with certain bacteria, such as Pseudoalteromonas tetraodonis, which produces a powerful toxin called tetrodotoxin. This toxin helps protect them from being eaten by predators.
Feeding and diet
Black-Spotted Porcupinefish are nocturnal feeders. Their diet mainly includes hard-shelled prey such as crustaceans (crabs and shrimp), gastropods (snails), and sea urchins. They use their strong jaws and beak-like teeth to crack open these tough shells with ease.
Reproduction
Black-Spotted Porcupinefish are prolific spawners. During spawning, males push females to the surface where they release and fertilize a large number of eggs. These eggs float on the surface for several days before hatching into well-developed larvae. Over the next three weeks, the larvae grow fins and teeth and, once they reach about 6 to 7 cm, they migrate to inshore areas in search of shelter and better food sources.
Fun Facts:
- Despite their charming appearance and unique features, Black-Spotted Porcupinefish aren’t the best swimmers. They have small fins and bulky bodies, making them slow and somewhat awkward in the water.
- An interesting tidbit from Charles Darwin: Dr. Allen of Forres often found porcupinefish still alive and inflated inside sharks’ stomachs. Some even managed to chew their way out, showing their impressive toughness!
- When inflated, porcupinefish can still swim, but the air trapped in their belly makes them float upside down at the surface. They draw in water through their mouth to help release the air and sink back to deeper water.
- The Black-blotched Porcupinefish is the only fish you’ll encounter on a dive around Koh Tao that seems to smile at you! They also have a unique ability to move each eye independently, allowing them to keep a constant lookout while swimming.
- Diodon comes from Greek, meaning "two-toothed," referring to the fused, beak-like teeth of these fish.
Where to Find Black-Spotted Porcupinefish on Koh Tao
You can spot the Black-Spotted Porcupinefish while scuba diving at various dive sites around Koh Tao. Though they can be a bit shy, you’ll often find them hiding under ledges and between rocks at different spots :
