Pacific red gurnard
The bluefin gurnard or Pacific red gurnard (Chelidonichthys kumu) is a species of marine ray-finned fishes belonging to the family Triglidae, the gurnards and sea robins. Its Māori names are kumukumu and pūwahaiau. It is found in the western Indian Ocean and the western Pacific Ocean, being common around Australia and New Zealand at depths down to 200 metres (660 ft). The fish is one of the most important commercial fish species in New Zealand.
The bluefin gurnard is a bottom-dwelling fish known for its bright red body and large, colourful pectoral fins with a large black eye-spot in the center and surrounded by a bright blue edge. Its natural colour is a splotchy pale brown, generally only becoming red when stressed and the belly is paler or even white.
It has a boxy, bony head which is protected by backwards-facing spines along the front of the snout and around the eye as well as on the hind margin of the operculum and tapers into a laterally elongated body with 33-35 vertebrae.
There are 8-10 gill rakers and 70-80 scales on its lateral line, which is uninterrupted. Its two tall, triangular dorsal fins have a total of 15-16 soft rays and 9-10 spines. There is no adipose fin. The anal fin has 14-16 soft rays and no spines.
The bluefin gurnard's large, fan-like pectoral fins are one of two pairs with 13-14 soft rays and its pelvic fin has 5 soft rays and a single spine. The pectoral fins’ first three rays are modified and separated from the rest of the fin. They are used as sensory organs, sometimes referred to as “fingers”, permitting it to probe the sea bottom to detect prey buried in the sand or the mud These spectacular fins make the red gurnard look like a butterfly of the sea, however their role is not entirely known. They could be used to attract a mate or frighten off predators. These fan-like fins can also be used to give stability during swimming.
The bluefin gurnard can be found throughout many central tropical and temperate Indo-West Pacific waters. It is commonly found along the coasts of New Zealand, Australia, South Africa, and many islands in the South Pacific. It is unsure whether or not previous records from Japan, Korea, China, and the Hawaiian Islands are mis-identifications.
The bluefin gurnard is the most common gurnard in New-Zealand. It is found in all the coastal waters around both the north and south islands except the southern fiords, and also Stewart, the Chatham, and Kermadec Islands. There are large population hotspots around the Bay of Plenty, Hawke Bay, Banks Peninsula, the Foveaux Strait, the west coast of the North Island, and the north and northwest coasts of the South Island.
As a benthic marine fish, the bluefin gurnard prefers shallow coastal waters and may be found from the edge of continental shelves to estuaries and brackish rivers) with soft bottoms of sand, sandy-shell, or mud. This is because they 'walk' slowly over the seabed using their first three free-rays. They can bury themselves in the substrate, with only the top of their head, their nostrils and eyes exposed in order to surprise prey (Lang, 2000). It is found from shallow waters one meter deep but generally inhabits 100-200m but may have maximum depths of up to 300m.
Bluefin gurnards are known to be quite vocal when captured, emitting loud grunts. Although referred to as "vocalisation", sounds are not actually made through laryngeal mechanics but are thought to be produced by contracting pairs of intrinsic sonic muscles in the swim bladder. The growling sound is a nocturnal vocalisation emitted at night and singly, whereas the grunts is produced when the animals are grouped. Grunts sounds last 0.2 seconds and can be heard without any advice, their frequency range are from 250 to 300 Hz. The fish is believed to be the loudest species in the Triglidae family.
A study of a captive female red gurnard and discovered four separate types of sound it can produce in two separate aural categories: grunt and growl. Its vocalizations were heard every hour around the clock with increases at dawn and dusk, and growls were made at night. The sounds were not found to be associated with feeding activity and in this setting were unlikely to be distress. The vocalizations may indicate associations with reproductive state as they are known to make the most noise during breeding season and generally are “likely to be significant contributors to ambient underwater soundscape.”
The bluefin gurnard is an opportunistic feeder, preying principally on crustaceans but pretty much any small macrofauna such as shrimp/prawns, crabs, crayfish, lobster, amphipods, small fish, and polychaete worms. It uses modified fin rays under its pectorals to probe the sand for prey and may also use the large fan-like pectoral fins to offer prey mock shelter. They can be found in shallow water with soft ground after being stirred by winter storms and around the seasonal migrations of small shoreline fish like whitebait, anchovy, and pilchard.
Along the Australian shores, the bluefin gurnard seems to be one of the apex predators with dogfishes, dories, lings and other flatheads.
A possible use for its large pectoral fins may be to make it appear larger to scare off potential predators.
