This family contains only one species. It is characterised by a compressed and oblong body; small, toothless and terminal mouth; non-protractile upper jaw; lateral pouches on the posterior part of the branchial chamber forming an epibranchial organ; presence of intermuscular bones; first 3 vertebrae specialised in structure; presence of an alarm substance; swimbladder present; gill membranes united and not attached to the isthmus; caudal fin deeply forked; the dorsal and pelvic fins opposite and small to moderate; cycloid scales; and a distinct lateral line.

Genus Chanos
Lacepède, 1803

Characters for the only species in the genus and family are summarised under the family.

Chanos chanos
(Forsskål, 1775)

Common names

khameh mahi (= literally cream fish but probably meant as milkfish).

[sheem in Arabic; milkfish, salmon herring, giant herring].

Systematics

No major synonyms. Mugil chanos was originally described from Jidda on the Red Sea.

Key characters

The milkfish resembles members of the family Clupeidae but is distinguished by a low number of branchiostegal rays (4 as opposed to 6-7), the presence of a lateral line, and the absence of scutes along the belly.

Morphology

The mouth is small and lacks teeth. There is a notch on the upper jaw in the mid-line into which a lower jaw protuberance fits. The large eyes have an adipose eyelid. The intestine is very long with many folds. The lower part of the oesophagus has a "gizzard', an area with longitudinal folds.

Lateral line scales 70-92, with 3-11 on the tail fin this latter count varying widely between authors. Total dorsal fin rays 13-17 including usually 2-6 unbranched rays, branched dorsal fin rays 9-14, usually 11-12; anal fin unbranched rays 2-3, branched rays 6-10, usually 7-8; pectoral rays 14-18, usually 15-16 and pelvic branched rays 10-12. Gill rakers and pyloric caeca very numerous. Gut long and complexly coiled. Vertebrae 42-46. Chromosome number 2n=32, low compared to other primitive teleosts (Klinkhardt et al., 1995).

Meristic values for Iranian specimens are:- lateral line scales 70(1), 71(2), 72(1), 74(2), 75(1), 76(2) or 79(2); unbranched dorsal fin rays 4(11); branched dorsal fin rays 11(7) or 12(4); unbranched anal fin rays 3(11); and branched anal fin rays 7(10) or 8(1); pelvic fin branched rays 9(1), 10(4) or 11(6); vertebrae 42(2) or 43(9).

Sexual dimorphism

None reported.

Colour

The overall colour is silvery with bluish or olive tints dorsally. The flank may have golden tints. The top of the head is yellowish-olive, the sides and ventral surface bright silvery to whitish. The snout is a light brown. The dorsal and caudal fins are colourless to grey, yellowish or brown with dark margins. The anal and pelvic fins are white, the anal with a dark margin. The peritoneum is black. The iris is silvery.

Size

Up to 1.85 m and 18.6 kg, although Bagarinao (1994) cites 1.5 m and 14 kg as more reasonable.

Distribution

Found from the African coast, Red Sea and Persian Gulf to the southern Pacific coast of the U.S.A. and to Peru, and north to Japan and south to Australia. Reported to penetrate 100 km up the Shatt al Arab (McKinnon and Vine, 1992).

In Iran, this species is reported from the Baghu River, Hormozgan near Bandar-e Abbas in 1976, found dead in brackish water about 14 km by river from the sea (Coad, 1981b). Also reported from the lower Mand River in Bushehr Province by M. Rabbaniha (pers. comm., 1995). Abdoli (2000) illustrates it as entering several rivers around the Straits of Hormoz including the Minab and Kul rivers. Salehi (1999) records this species from estuaries in Hormozgan and Makran including the "Khoor-Chel", Shur, "Takhtenze", Tiab, Gask, Heylaru, "Gorginee" and Gabrik rivers.

Zoogeography

The milkfish is unusual in being one of the few Indo-West Pacific fish species found also in the eastern Pacific, although the mechanism of dispersal is uncertain. Larvae are probably incapable of crossing the 6500 km wide East Pacific Barrier but adults could do so as they can cruise at 2 km/h. However adults have not been caught on the high seas.

Habitat

Usually found in littoral waters of the ocean, rarely entering rivers, but it has been acclimatised to freshwater ponds. It becomes sluggish at temperatures below 15°C and dies at about 12°C but can survive temperatures of 41°C. It seems to prefer waters warmer than about 20°C. The Iranian specimens (Coad, 1981b) were caught at 16°C in a shallow, muddy, backwater and probably died through exposure to colder temperatures in the main river. Persian Gulf temperatures can fall below 15°C in winter.

It is resistant to salinity changes and can survive in fresh and hypersaline water (0-158 p.p.t.) as well as waters low in oxygen. The dorsal and upper caudal fin lobes may cut the surface of the water and milkfish are often mistaken for sharks. Milkfish are solitary or found in small schools.

Age and growth

Life span is at least 12 years based on pond specimens but large adults in the sea undoubtedly live much longer. Growth in the sea is poorly known and most data refer to pond-reared populations. Fish at sea are 20-43 cm long after 1 year, a growth rate considerably less than in ponds. Maturity is reached at 3-5 years in the wild but as long as 8-10 years in ponds.

Food

Young and adult milkfish will feed on surface scum, taking it in with a smacking noise. Benthic and epiphytic organisms are also taken in ponds with the body inclined at an angle of about 30°. Cyanobacteria, benthic diatoms, foraminiferans, filamentous green algae, detritus, clams, snails, worms, some crustaceans, and fish eggs and larvae are taken in from the sea floor. Other reports have this species feeding on plankton but this may be detritus fallen to the sea floor from surface layers

Reproduction

There are two spawning seasons in India, March to June and September to November but individuals may only spawn once a year. Spawning occurs in clear water of sheltered, sandy bays within about 6 km of shore, away from river mouths, i.e. saline water, and is probably triggered by rising temperatures in spring (25-30°C) and high tides. These conditions give water deep enough to avoid eggs being eaten by corals and other benthic organisms yet close enough to shore for larvae to reach their preferred inshore habitats. Eggs are fertilised while floating in surface waters. Fecundity is reported to reach 7.3 million eggs but this is not based on large fish and fecundity could be considerably more. Egg diameters are up to 1.25 mm when fertilised. Ribbon-like larvae migrate to coastal areas, metamorphose and may enter creeks and estuaries. About 4 weeks later the young leave coastal waters and spread out in waters where there are adequate supplies of benthic and planktonic food. Some may remain in estuarine areas for 4 years before returning to the sea. In February-March, and again in October in some populations, the adult migration to inshore waters for spawning takes place. Adults leave coastal waters after spawning.

Parasites and predators

Young are eaten by a wide variety of predators in nearshore waters as indicated by the high egg production and adult survival rate.

Economic importance

This is the most important tropical marine fish used in aquaculture with a history dating back 500 years. Milkfish are raised in brackish or freshwater ponds throughout Asia, but not Iran, based on larvae captured in shore waters. 1.35 billion larvae were caught in the Philippines in 1974. The Philippines, Indonesia and Taiwan produce about 330,000 tonnes of milkfish per year. Their wide tolerance of environmental variables and herbivorous diet (rice bran and pelleted foods in captivity) combined with fast growth make them a success in aquaculture. The fish are marketed at 200-300 g. Adults form part of fisheries aimed at other species.

McKinnon and Vine (1992) report that this species is sold in the fish market at Basrah, Iraq. In the Persian Gulf they can be caught by set nets, gill nets, traps and hook-and-line (Carpenter et al., 1997).

Milkfish have been cultured in concrete ponds at Tiyab, Hormozgan from March to October. Fry were caught in local estuaries such as the Shur River 30 km east of Bandar Abbas. They were fed commercial carp food pellets and after 7 months weighed 450 g, or on poor protein food 130 g after 11 months with no growth in the cold season (Annual Report, 1995-1996, Iranian Fisheries Research and Training Organization, Tehran, p. 40, 1997; Forughi-e-Fard and Gharibnia, 1998; Fourooghi-e-Fard, 2000).

Milkfish have been reported as being ciguatoxic (intermittently poisonous through feeding on toxic food) (Bagnis et al., 1970).

Robins et al. (1991) list this species as important to North Americans. Importance is based on its use as food and as bait, in aquaculture and in textbooks.

Conservation

None required as this species is probably an accidental visitor to Iranian fresh waters.

Further work

The culture of this species in southern Iran could be developed further.

Sources

Biology was based on Schuster (1960) and Bagarinao (1994).

Iranian material: CMNFI 1979-0142, 11, 70.5-98.5 mm standard length, Hormozgan, Baghu River (27º17'N, 56º28'E) (Coad, 1981b).