Chanos chanos (Forsskal, 1775)

Chanos chanos View in CoL View Figure

Common name. Milkfish.

Diagnosis. Distinguished from superficially similar Clupeids by having four branchiostegal rays (vs. 6–7 in Clupeiformes ) and no scutes along the belly (vs. present). Size up to 1850 mm SL and 18.6 kg, usually less than 1500 mm SL and 14 kg.

Distribution View Figure . West Asia: Red Sea, Persian Gulf, and Gulf of Oman and along coasts of Arabian Peninsula. May be only a summer visitor in northern Red Sea and Persian Gulf. Widespread in tropical Indo-Pacific but absent from areas affected by cold currents. Distribution coincides with coral reef areas where water is warm (>20°C), clear and shallow. Migrates up to 100 km inland from Shatt al Arab/Arvand.Also reported from Baghu near Bandar-e Abbas,lower Mand,and Shour-Shirin or Tiyab estuaries. Likely to be found at least occasionally in all major estuaries in Persian Gulf basin.

Habitat View Figure . Marine. Juveniles enter estuaries and lower parts of rivers. Can acclimatise to freshwater. Adults occur near coasts or around islands where reefs are well developed. Spawns in marine waters in sheltered sandy bays less than 30 km from shore.

Biology. Age unknown in wild due to lack of aging method. Lives up to 12 years in ponds, but large wild adults are thought to be much older. Mature at 3–9 years in ponds. A warm water species, preferring water temperatures above 20°C, can survive up to 41°C. Dies at about 12°C. Euryhaline, can survive in fresh, marine, hypersaline waters (0–158 ‰). Very resistant to low dissolved oxygen, high ammonia, nitrite concentrations, crowding, and starvation. Spawning season long near equator becomes progressively shorter with a single peak at higher latitudes. Spawning thought to be triggered by rising spring temperatures (25–30°C) and high tides. Adults migrate offshore from coastal waters after spawning. High fecundity with very small eggs,0.3–1.0 million eggs per kg body weight, 1.1–1.2 mm in diameter when fertilised. Hatching varies from 20 to 25 hours after fertilization at 26–32°C and 29–34 ‰ salinity. Eggs and ribbon-like larvae, pelagic up to 2–3 weeks. Eggs sink at salinities below 30 ‰. Larvae metamorphose and, at 10–17 mm TL, migrate ashore and settle in coastal wetlands (mangroves, estuaries). After about 4 weeks, most juveniles leave coastal waters.Some remain in estuaries for up to 4 years before returning to sea. Occasionally enters freshwater during juvenile stage. Grows to 200–430 mm TL in a year in wild. Larvae and small juveniles feed on copepods and diatoms. Larger juveniles are mainly herbivorous, feeding on cyanobacteria, algae, detritus, and small invertebrates grazed from substrate. Adults are opportunistic feeders, filtering, grazing, or snatching small prey and taking larger quantities of zooplankton and small fish.

Conservation status. LC; conservation status of wild populations is poorly known. Research is strongly focused on aquaculture aspects.

Further reading. Juario et al. 1984, Lee et al. 1986 (biology).