Milkfish


The milkfish is a widespread species of ray-finned fish found throughout the Indo-Pacific. It is the sole living species in the family Chanidae, and the only living member of the genus Chanos.
The repeating scientific name is from Greek . They are grouped in the order Gonorhynchiformes and are most closely related to the Ostariophysi—freshwater fishes such as carps, catfish, and loaches.
The species has many common names. The Hawaiian name for the fish is awa, and in Tahitian it is ava. It is called bangús in the Philippines, where it is popularly known as the national fish, although the National Commission for Culture and the Arts has stated that this is not the case as it has no basis in Philippine law. In the Nauruan language, it is referred to as. Milkfish is also called bandeng or bolu in Indonesia.

Geographic distribution

Chanos chanos occurs in the Indian Ocean and across the Pacific Ocean, from South Africa to Hawaii and the Marquesas, from California to the Galapagos, north to Japan, south to Australia. A single specimen was reported in 2012 in the eastern Mediterranean Sea.
In 1877, the California Fish and Game Commission introduced one hundred milkfish from Hawaii to the inland waters of Solano County, California. The introduced population could not establish itself permanently and it is currently unknown how their presence affected the native ecosystem.
Milkfishes commonly live in tropical offshore marine waters around islands and along continental shelves, at depths of. They also frequently enter estuaries and rivers.

Taxonomy

Chanos is the only surviving genus of the ancient family Chanidae, which has existed since the Early Cretaceous. The only surviving species is the widespread C. chanos. The genus Chanos originated in North America, with the oldest known fossil species dating as far back as the earliest Paleocene around in Mexico. The earliest fossil Chanos were found in freshwater Eocene deposits in Europe and North America—hinting that the species first appeared in freshwater environments 40–50 million years ago. It is possible that their invasion into the ocean happened during high sea-level or flooding events after the Eocene. Global cooling during the Mid-Eocene likely wiped out the population of milkfish in the Atlantic, but the species persisted in the Indo-Pacific.
The following fossil species of Chanos are known:
The extinct Caeus leopoldi from the Early Cretaceous of Italy is also sometimes placed in Chanos as Chanos leopoldi, which would be the earliest record of the genus and extend its occurrence even further back. However, more recent studies have affirmed it being a distinct genus.

Anatomy

The milkfish can grow to, but are most often no more than in length. They can reach a weight of about. and an age of 15 years. They have an elongated and almost compressed body, with a generally symmetrical and streamlined appearance, one dorsal fin, falcate pectoral fins and a sizable forked caudal fin. The head is small relative to the body. The mouth is small and toothless. The body is olive green, with silvery flanks and dark bordered fins. They have 13–17 dorsal soft rays, 8–10 anal soft rays and 31 caudal fin rays. There are numerous fine intramuscular bones, which may complicate human consumption of the fish.
Their silvery complexion is similar to many other fish species of the Indo-Pacific. They are often mistaken for species of Clupeidae, Megalops cyprinoides, Gonorhynchus gonorhynchus, and Elops machnata. Chanos can be distinguished from these species by their size, absence of scutes, tubercle on the lower jaw, fin placement, no gular plate between arms of the lower jaw, and having only four branchiostegal rays.
Variant milkfish body types have occasionally been found. The "goldfish-type" milkfish was discovered in the Philippines and is characterized by distinctly elongated dorsal, pelvic, and anal fins, and a caudal fin as long as the body. In Hawaii, Indonesia, and Australia, dwarf or hunchback 'shad-type' specimens have been recorded. They have a standard length-to-depth ratio of 2.0-2.5 instead of the usual 3.5-4.0. In Northern Australia, a milkfish with a red head, red fins, and blue dorsal coloration was reported.

Life history

Reproduction of milkfish in nature is far less understood than populations of milkfish bred and propagated in captivity. In the wild, milkfish take 3–5 years to mature. Females can produce 0.5-6 million eggs and have the ability to spawn more than once a year. Spawning takes place at night, may be lunar periodic, and is strongly seasonal. Milkfish eggs are pelagic and range between in diameter. Spawning sites are clear, warm, shallow waters above sand or coral reefs. It is believed milkfish prefer these locations to minimize predation from benthic planktivores.
Milkfish larvae have a pelagic planktonic stage. Younger larvae occur mostly at the surface, or sometimes deeper. Older larvae are only found at the surface and in near-shore environments. Larvae metamorphose into fry and become benthic-feeding juveniles that are opportunistically herbivorous, detritivorous, or omnivorous, depending on the predominant food types in the habitat.
Juvenile milkfish larger than typically bear the characteristics of adults. They have complete fin rays, a forked caudal fin, scales, and silvery coloration. Juveniles have been found to inhabit a diverse range of shallow-water ecosystems such as coral lagoons, estuaries, marsh flats, tidal creeks, and tide pools.

Diet

Milkfish are omnivorous opportunistic feeders. Juvenile milkfish eat a variety of foods including phytoplankton, zooplankton, filamentous green algae, and small invertebrates. Similarly to juveniles, adults also eat benthic invertebrates and additionally planktonic and nektonic items such as clupeid juveniles.

Habitat

Adults tend to school around coasts and islands with coral reefs. The young fry live at sea for two to three weeks and then migrate during the juvenile stage to mangrove swamps, estuaries, and sometimes lakes, and return to sea to mature sexually and reproduce. Juveniles prefer to settle in undisturbed coastal ecosystems that are semi-enclosed, calm, shallow, free from predators, and rich in aquatic vegetation. In their natural habitats, milkfish are very adaptable to both changes in environmental conditions and diet. Milkfish are good osmoregulators and extremely euryhaline.
The wide geographic distribution of milkfish has led to genetic variation in the species across the Indo-Pacific. Milkfish populations differ between the Hawaiian islands, the central Pacific islands, Tonga, Tahiti, Philippines-Taiwan-Indonesia, Thailand-Malaysia, India, and Africa. However, all populations are thought to be inter-breeding, thus they are all considered one species, and their genetic diversity is low. However, populations may still differ in their reproductive, migratory, and survival methods.

Conservation status

According to the International Union for Conservation of Nature, as of 2019, milkfish were not a threatened species. However, little information is available on wild stocks.
Although milkfish populations are not threatened with extinction, they are at risk of ingesting or absorbing pollutants. Milkfish frequent environments that have been affected by industrial pollutants, land runoff, and plastics. Asia is one of the largest contributors of plastic litter into both the ocean and freshwater systems. A population of milkfish from San Jose, Northern Samar, Philippines, was found to have concentrations of lead in the meaty part of their bodies. Pollutants have also affected the aquaculture industry. In an aquaculture system in Butuan, Philippines, 97% of the fish sampled had microplastics in their gastrointestinal tracts. A similar study in Indonesia showed similar results. The presence of pollutants in milkfish poses a threat to the species' health, aquaculture, and humans.

Fishing

In the Philippines, it is prohibited to fish for adult milkfish, also known as sabalo, over. The government enacted this law in 1975 in an effort to protect spawning stocks of fish. However, sabalo are incidentally caught in fish corrals and are products of bycatch from fisheries. The ban was reinforced by the Philippine Fisheries Code of 1998 and violations are punishable by imprisonment for 6 months to 8 years, and/or a fine of, forfeiture of the catch and fishing equipment used, and revocation of the fishing license.

Consumption

The milkfish is an important seafood in Southeast Asia and some Pacific Islands. Because it is notorious for being much bonier than other food fish, deboned milkfish, called "boneless bangús" in the Philippines, has become popular in stores and markets. Despite the notoriety however, many people in the Philippines continue to enjoy the fish cooked regularly or even raw using kalamansi juice or vinegar to make kinilaw na bangus.
Popular presentations of milkfish in Indonesia include bandeng duri lunak from Central and East Java or bandeng presto, which is pressure cooked milkfish until the thorns are rendered tender, and bandeng asap or smoked milkfish. Either fresh or processed, milkfish is the popular seafood product of Indonesian fishing towns, such as Juwana near Semarang in Central Java, and Sidoarjo near Surabaya in East Java.
Milkfish is the most popular fish in Taiwanese cuisine; it is valued for its versatility as well as its tender meat and economical price. Popular presentations include as a topping for congee, pan fried, braised, and as fish balls. There is a milkfish museum in Anping District and city of Kaohsiung holds an annual milkfish festival.
Milkfish is an oily fish, and is rich in omega-3 fatty acids.