Part 3—Reef Fish
Fish exhibit a diverse array of life styles to cope with living together in the crowded and competitive world of the reef. Some species are always found in groups while others occur in pairs or are solitary. On a typical coral reef more than 75% of the fish spend the daylight hours on the surface of the reef or a short distance above it.
Butterflyfish are small, colourful, disc like fish with small protractile mouths with small brush-like teeth. Many feed on coral polyps hence their specialised mouths. They patrol a home range and if they feed on coral polyps are highly territorial around the areas of their food source. Many species occur as heterosexual pairs that may remain together for years, if not life.
Image: Redfin Butterflyfish
Jacks and Trevallies
Jacks and Trevallies are medium to large compressed silvery fish; a narrow bony section usually reinforced by a series of bony scutes joins the forklike tail to the body. Trevallies are fast swimming predators of the waters above the reef and open sea. They mainly feed on fish and crustaceans, often hunting juvenile fish by rushing towards the reef to grab an unsuspecting victim. They are an important food fish to man.
Image: Bluefin Trevalley
Groupers are medium to large robust bodied forms with large ‘grumpy’ looking mouths. The jaws contain bands of small teeth and canines in front. Typically they are bottom dwelling and feed on fish or crustaceans. Generally a camouflage predator, sitting and waiting, blending into the reef, it uses its large mouth to create a vacuum and thus sucking in its prey. Groupers generally spawn in aggregations leaving them vulnerable to overfishing.
Image: Hexagon Coral Grouper
Wrasses are a large and diverse group in both size and form. Typically wrasses have a terminal mouth with somewhat thickened lips and often have one or more pairs of protruding canine teeth. Their bodies are elongate, and cigar shaped for most of the group. Typically the wrasse change colour with growth and sex. They have a drab juvenile phase starting off as a female and then with growth change sex into a brilliant coloured male phase.
Image: Six-Bar Wrasse
Scissortail Sergeant Damselfish are small fish with compressed bodies, they have small terminal mouths with conical teeth. Their distinctive bars on their back give them their ‘sergeant’. They often aggregate in high water feeding on plankton and small algae. They are common fish to be spotted in the Mamanuca area.
Image: Scissortail Sergeant Damselfish
Surgeonfish are oval to elongate compressed fish with a small terminal mouth containing a single row of small close-set incisors. The tail has a scythe or crescent shape. They have a tough skin with minute scales and often one or more pairs of sharp blades at the base of the tail. The blades may be used offensively or defensively and can inflict deep painful wounds, hence the name surgeonfish. The unicorn fish also belongs to this family and have a bony protrusion coming from the forehead, hence their name. They also have generally two pairs of hook like blades at the base of their tail. Surgeonfish are important herbivores on the reef, grazing on algae in large schools.
Image: Yellowfin Surgeonfish
This is part 3 of 4 in the Common Reef Creatures series.