Fish Classifications

There are more than 1500 species of fish living in the Great Barrier Reef. They come in a variety of shapes, sizes and colours. The smallest fish, the Goby is just 1 cm in length. The largest fish on the reef are the giant Groupers and Cods that can weigh up to 400 kg.

Fish Characteristics

  • All reef fish have a skeleton made of bone
  • One gill opening at each side of the head
  • A swim bladder
  • Reproduction through external fertilisation
  • Fish have 2 layers –an outer skin or epidermis and an inner skin or dermis
  • Most fish are covered in scales
  • Fish can live in a variety of habitats

Fish Shapes

The shapes and sizes of fish vary between different species; however there are 5 main types of fish body shapes:

  • Streamlining
  • Laterally compressed
  • Vertically compressed
  • Elongated
  • Unusual

Streamline fish are fast swimming and live in more open oceans. Fish with a streamlined body shape include sharks, trevally, mackerel and fusiliers.

Laterally compressed shape fish swim in bursts to escape from predators or to capture food. They have a shape that is ideal for swimming around coral reefs. Fish with laterally compressed body shapes include; angelfish, batfish and butterfly fish.

Vertically compressed shape fish are flattened from the top to the bottom and live and swim on the bottom of the ocean floor. Fish with vertically shaped bodies are; flathead fish, sole fish and ray species.

Elongated shape fish include eels and pipe fish and trumpet fish. Their shape is ideal for moving in and out of narrow spaces, rocky coral reefs and vegetated areas.

Unusual shaped fish are usually very slow moving and have a unique body shape. These fish include seahorses, puffer fishes and stone fish.

Surprisingly, the bulk of fish species typical on the Great Barrier Reef belong to a small group of families. Collectively the ten most abundant families constitute as much as 60 to 70 percent of all fish at any one particular reef.

Reef fish can be divided into six categories

  1. Colourful coral associates, like anemone fish and butterfly fish
  2. Cryptic fish like blennies, gobies and seahorses that can be difficult to see because of their camouflage or where they live
  3. Grazing fish like the surgeon fish, parrot fish and the wrasse
  4. Pelagic reef fish include the bat fish and fusiliers
  5. Reef predators include snapper, cod, groupers and emperors
  6. Nocturnal  cave dwellers include eels, scorpion fish, solider fish and squirrel fish


Gender is somewhat fluid in fish. Changing sex is common in most species.

Species Description  

  1. Damsel fish form large plankton eating schools, others blanket the reefs surface. Male damsel fish guard nests of eggs during a 2 to 7 day incubation period
  2. Wrasses are colourful fish that inhabit all reef environments. They feed on small vertebrates. Individual reef areas will usually have a dominant male and smaller females. Most Wrasse species are capable of female to male sex change.
  3. Butterfly fish have beautiful colour patterns and a graceful appearance. Many of the butterfly fish feed exclusively on living coral polyps and they often mate for life.
  4. Angel fish have very distinctive colours and patterns, feeding on sponges and smaller invertebrates.
  5. Cardinal fish are nocturnal, hiding in amongst the corals during the day. At night they feed on small shrimps and crabs.
  6. Groupers are the largest of all the reef fish. The Queensland grouper can grow up to 400 kg.
  7. Parrot fish are a close relative to the wrasse and is one of the dominant algal feeders on the reef. Females and juveniles are much less colourful than the males. Individuals are capable from female to male sex change. The parrot fish eats a considerable amount of coral rock whist feed on the algae. The parrot fish have a large beak like appearance for teeth and a second set of jaws in their throat, that ground up the coral into a fine powder that is passed through their body.
  8. Surgeon fish species are often found in schooling groups that graze on the filamentous algae that mat over the coral surface. The surgeon fish have scalpel like appendages at the base of their tail which are used as a defence mechanism.
  9. Blennies are a small territorial bottom dweller. Blennies are often seen as individuals or in small groups. Blennies lay their eggs in the crevices of the coral and coral rock or even in abandoned shells and worm tubes. The male of the species will guard the eggs until they hatch.
  10. Gobies are small bottom dwelling fish that are most abundant of fish species on the Great Barrier Reef. Gobies can grow to the length of 1 to 5 cm and live in the shelter of corals and coral rock.