The giant grouper is the largest of all reef-dwelling bony fish, growing up to 8.9 feet (2.7 m) in length and weighing up to 660 pounds (300 kg). This massive fish can be found among reefs, caves and wrecks in shallow Indo-Pacific waters. A highly adapted ambush predator, the giant grouper will hide in holes, crevices or reef overhangs, and remain nearly motionless while waiting for unsuspecting prey to come close enough to strike. Its eyes see well in the dark, and can rotate, allowing the grouper to spot approaching prey without even moving its head. When the grouper opens its large mouth, it creates a powerful suction and draws in its target, which it swallows whole. At the upper end of its food chain, the giant grouper feeds on a variety of prey, including fish, crustaceans, juvenile sea turtles, and even small sharks.
  • Size

    8.9 feet (2.7 m) and maximum weight of 660 lbs (300 kg).
  • Diet

    Fish, sharks, juvenile sea turtles and crustaceans, including spiny lobster and mud crabs
  • Range

    Indo-Pacific from the Red Sea to Algoa Bay, South Africa through the Hawaiian and Pitcairn islands and south to Australia
  • Habitat

    Tropical shallow reefs, caves, wrecks and estuaries

Physical Characteristics

Size

  • Largest of all coral reef-dwelling bony fish.
  • Common length of 6.2 feet (1.9m), with a maximum length of 8.9 feet (2.7 m).
  • One of the largest recorded was 9.8 feet (3 m) and weighed more than 882 lbs. (400 kg).

Body Composition

  • Has a very large mouth that expands and protrudes to create a strong suction to draw in prey.
  • Mouth has at least seven rows of teeth on the middle of the lower jaw.
  • The giant grouper’s eyes function effectively in dim light, which gives it an advantage over its prey during dawn and dusk feeding times.
  • Eyes also rotate so grouper can see approaching prey without moving its head.

Color

  • Juvenile giant grouper are bright yellow with large, irregular black or dark brown bars.
  • As adult, irregular patterns break up and their coloring becomes a muted, mottled olive-gray.

 

Animal Fact

Because it is long lived and late to reproduce, the giant grouper is highly susceptible to overfishing. Fishermen generally target larger individuals, meaning that, frequently, too many breeding specimens are removed from a population to it to sustain itself

Diet / Feeding

Diet

  • Consists of fish, sharks, juvenile sea turtles and crustaceans, including spiny lobster and mud crabs.

Feeding

  • Ambush predator that lies in wait while hiding in holes, crevices and reef overhangs.
  • Swallows food whole.
  • Occupies the upper end of the food chain.
  • Few reside in each area; few found on any one reef.

 

Range / Habitat

Range

  • Occurs in the Indo-Pacific from the Red Sea to Algoa Bay, South Africa through the Hawaiian and Pitcairn islands and south to Australia.

Habitat

  • Found in tropical shallow reefs, caves, wrecks and estuaries commonly to 164 feet (50 m) deep. Full depth range is 13-328 feet (4-100 m).

Reproduction & Growth

Reproduction

  • Protogynous hermaphrodite; starts out life as female and can later change gender to become male.

Growth

  • Does not reach sexual maturity until it is about 20 years old. Fishing usually removes the largest, and therefore oldest, fish first.

Conservation Status

  • “Vulnerable” on IUCN Red List.
  • Population thought to be declining 20 percent rate every ten years.
  • Populations of this species have been drastically reduced worldwide due to overfishing.

Additional Information

  • Slow-growing and lives up to or beyond 50 years.
  • Other common names for this species are “Queensland grouper” and “brindle bass.”

Sources

  • Encyclopedia of Fishes. 2nd Edition, pgs. 195 -199
  • Fishes of the Great Barrier Reef. Randall, J. E., pg. 109
  • Fishes of the Tropical Eastern Pacific. Allen, G. R., pg. 106
  • Reef Fish. Thresher, R. E., pgs. 153 -155
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