Caranx sp.

The Indian threadfish (Alectis indica), also known as the Indian threadfin, diamond trevally, mirror fish or plumed trevally, is a large species of coastal marine fish of the jack family, Carangidae.

DISTRIBUTION AND HABITAT

• The Indian threadfish is commonly found in the tropical waters of the Indian and Western Pacific Oceans, spanning from Madagascar and east Africa to India, China, Southeast Asia, and as far north as Japan and south to Indonesia and northern Australia.

• Typically dwelling in coastal waters at depths ranging from 20 m to 100 m, although juveniles may sometimes be found in pelagic environments, carried by ocean currents. Juveniles of the Indian threadfish are also known to inhabit estuaries in various other regions, as well as seagrass beds. Adult specimens are predominantly found in reef areas below 20 m in depth.

DESCRIPTION

BODY STRUCTURE:

• Resembles a large jack.

• Angular and strongly compressed body.

• Distinguishing head profile with slight concavity near eyes.

• Dorsal profile more curved than ventral.

• Greatest body depth between soft dorsal and anal fins.

FINS:

DORSAL FIN:

• First section: 5 to 7 visible spines.

• Second section: One spine and 18 or 19 soft rays.

ANAL FIN:

• Two spines followed by a single spine and 15 or 16 soft rays.

PECTORAL FIN:

• Long and curved, extending beyond lateral line junction.

SKIN AND SCALES:

• Appears scaleless but has minute, deeply embedded scales.

• Lateral line strongly curved anteriorly.

• 6 to 11 scutes toward the tail.

• Juveniles have long, filamentous trailing anal and dorsal fin spines.

SIZE:

• Known to grow up to 165 cm in length and 25 kg in weight.

COLORATION:

ADULT:

• Silvery blue-green above, darkest on head, silver below.

• Small diffuse dark spot on upper operculum.

• Long filamentous fins and pelvic fin dark blue to black, others pale green to hyaline.

JUVENILES:

• Exhibit 5 to 7 broad dark vertical cross bands on body.

ECOLOGY

• The Indian threadfish, a predatory species, consumes a diverse array of prey, including various fishes, small squids, jellyfish, and crustaceans. Similar to A. ciliaris, the juveniles possess trailing fins resembling jellyfish medusae, likely serving as a defense mechanism against predators.

•  Reproduction in the species remains relatively understudied, but observations in Indonesia indicate that spawning occurs in pairs during the daytime, typically between ebbing and flooding tides. These spawning events often take place in a shoal located at depths of 35–45 m within a deeper channel situated between two islands.

RELATIONSHIP TO HUMANS

• The Indian threadfish is a commercial fish of minor importance throughout its range, often forming part of artisanal fishery catches. Beach seines and hook-and-line methods are the predominant methods of capture.

• The species is commercially farmed in small numbers in Singapore using aquaculture techniques. These farmed fish generally sell for between 7 and 11 US dollars per kg, as high or higher than other jacks farmed in the country.

• Juveniles are moderately popular aquarium fishes, but require fairly large tanks and peaceful neighbours.