Chanos chanosAwa(Also: Awa kalamoho; Pua awa)

Geographic Range

Milkfish are native to regions in the Indian and Pacific Oceans. Their range spans from the east coast of Africa and Madagascar to the coasts of India and Southeast Asia around Malaysia, Indonesia, New Guinea, Australia, northward to the southern tip of Japan, and eastward into the Pacific Islands. (Bagarinao, 1994)

Habitat

Milkfish are usually found along the coasts of continents or islands, particularly where reefs are well developed. They also occur in large coastal lagoons. Milkfish are found in tropical waters, rarely in waters that are affected by cold ocean currents. They are found in clear, shallow, saline, and warm waters above 20°C. Adult milkfish also occur in freshwater lakes in the Philippines, Indonesia, and Madagascar. Juveniles are found in large coastal lagoons, atolls, and freshwater lakes. The depth range of the milkfish is 0 to 30 m. (Bagarinao, 1994)

  • Range depth
    0 to 30 m
    0.00 to 98.43 ft

Physical Description

Milkfish have a long, muscular, silvery body with a forked tail. The forked tail is fairly large and strong, thus making them fast and powerful swimmers of the open sea (Bagarinao 1994). Milkfish have large eyes, a pointed snout with a terminal mouth, and cycloid scales. The total length ranges from 50 cm to 180 cm (Bagarinao 1994, Gale 2003). They weigh between 4 and 14 kg (Bagarinao 1994). Milkfish have 13 to 17 rays in their dorsal fin, 6 to 8 anal rays, 15 to 17 pectoral rays, and 10 to 11 pelvic rays (Gale 2003). (Bagarinao, 1994; "Milkfish Chanos chanos", 2003)

There have been rare occurrences of variant forms of milkfish. One variant, found in the Philippines, has distinctly long dorsal, pelvic and anal fins, and the caudal fin is as long as the length of the body. This variant is the ‘goldfish-type’ milkfish. Another variant, seen in Hawaii, Indonesia, and Australia, is called the ‘shad-type’ milkfish because its length-to-depth ratio is 2.0 to 2.5 instead of the typical 3.5 to 4.0. (Bagarinao, 1994)

  • Sexual Dimorphism
  • sexes alike
  • Range mass
    4 to 14 kg
    8.81 to 30.84 lb
  • Range length
    50 to 180 cm
    19.69 to 70.87 in

Development

Fertilized milkfish eggs can be found in the open sea of tropical waters. The eggs are spherical in shape and range from 1.1 to 1.25 mm in diameter (Bagarinao 1994). The eggs have a yellowish yolk and lack oil globules. The outer embryonic membrane seems to be granular with a distinct, segmented pattern. There is a narrow perivitelline space present in milkfish eggs (Garcia 1990). Development of the embryo takes about 20 to 35 hours in water temperatures of 26 to 32°C and of salinity 29 to 34 ppt (Bagarinao 1994). (Bagarinao, 1994; Garcia, 1990)

Once the eggs hatch, the larvae are about 3.5 mm total length. At hatching, the larvae’s eyes are not pigmented and their mouth is not open (Bagarinao 1994). For about five days milkfish larvae depend solely on their yolk for nutrients (Garcia 1990). (Bagarinao, 1994; Garcia, 1990)

Milkfish larvae go through a series of complex morphological, physiological, and behavioral stages, which last about 2 to 4 weeks, before becoming juveniles. Younger larvae occur in water depths of 20 to 30 m, while older larvae occur near the water’s surface. Younger larvae occur both near and far from shore. More advanced larval stages begin to migrate towards nearshore areas, and are found most frequently there (Bagarinao 1994; Garcia 1990). Milkfish larvae migrate towards shore when they are about 10 to 17 mm total length (Garcia 1990). (Bagarinao, 1994; Garcia, 1990)

Once milkfish become larger than 20 mm total length they are considered juveniles. Juveniles appear to have the same characteristics and structure of adult milkfish (Garcia 1990). Juveniles enter brackish water and coastal wetland habitats where the food supply is more abundant. The kind of habitat, depth, and connection with the sea has been found to be the factors determining maximum size and duration of stay of juvenile milkfish in the nursery grounds (Bagarinao 1994). (Bagarinao, 1994; Garcia, 1990)

Growth and development of milkfish is influenced by water temperature. Temperatures between 23.7 to 33°C seem to be the optimal temperatures for development of milkfish larvae. The rate of development is faster at higher temperatures. Temperatures lower than 20°C and up to 22.6°C cause young milkfish to be rather sluggish, thus making them more vulnerable to predation. (Villaluz and Unggui, 1983)

Reproduction

Not much is known about mating systems and behaviors in milkfish. (Bagarinao, 1994)

Milkfish breed near shore in clean, clear, saline, warm, and shallow waters over sand or coral reefs. These spawning locations are as close as 6 km off shore (Bagarinao 1994) but are no more than 30 km off shore (Garcia 1994). Milkfish may spawn more than once a year and spawning usually takes place during the night. Spawning is highly seasonal and may be influenced by the lunar cycle (Bagarinao 1994). Milkfish breeding season is longer near the equator than at higher latitudes. The length of the spawning season may be influenced by surface water temperatures in certain areas (Garcia 1990). (Bagarinao, 1994; Garcia, 1990)

  • Breeding interval
    Milkfish may spawn more than once a year.
  • Breeding season
    Spawning usually takes place at night and may be influenced by the lunar cycle. Milkfish breeding may occur throughout much of the year, depending on latitude.
  • Range number of offspring
    0.5 million eggs to 6 million eggs
  • Range time to hatching
    20 to 35 hours
  • Range age at sexual or reproductive maturity (female)
    3 to 10 years
  • Range age at sexual or reproductive maturity (male)
    3 to 10 years

There does not appear to be any parental involvement once the eggs have been released into the water. (Bagarinao, 1994; Garcia, 1990)

  • Parental Investment
  • no parental involvement
  • pre-fertilization
    • provisioning
    • protecting
      • female

Lifespan/Longevity

Not much is known about natural mortality rates of adult milkfish, but the shortest recorded lifespan of milkfish is 3 years and the maximum lifespan is 15 years. Most mortality occurs at the egg and larval stages. (Bagarinao, 1994)

  • Range lifespan
    Status: wild
    3 to 15 years
  • Average lifespan
    Status: captivity
    15 years
    AnAge

Behavior

The behavior of milkfish is still one of the areas that has yet to be extensively studied. Large schools of milkfish have been seen in nearshore waters with well-developed reefs and in coastal lagoons, suggesting that they are social. (Bagarinao, 1994)

Communication and Perception

Not much is known about how milkfish communicate with one another during mating or how they perceive the environment. Like all fishes, they have a well-developed sensory system, including a lateral line system and a well-developed sense of vision. Milkfish are members of the Ostariophysi, which produce and respond to an alarm substance. This alarm substance is produced when the skin of the milkfish has been injured, particularly by a predator. This alarm substance warns other fish to seek a hiding place in order to avoid the predator. (Doving, 2000)

Food Habits

Milkfish feed on a variety of foods depending on the type of environment. As larvae they feed on zooplankton. As they develop into juveniles they start to feed on benthic items. The most common food items for juveniles are cynobacteria, diatoms, detritus, green algae, and invertebrates such as small crustaceans and worms. Adults feed on similar items, and on planktonic and nektonic prey such as clupeid juveniles. Adult milkfish have a well-developed epibranchial organ, which is an extension of the alimentary canal. The epibranchial organ allows milkfish to digest plant material (Gale 2003). (Bagarinao, 1994; "Milkfish Chanos chanos", 2003)

  • Animal Foods
  • fish
  • aquatic or marine worms
  • aquatic crustaceans
  • other marine invertebrates
  • zooplankton
  • Plant Foods
  • algae

Predation

Milkfish are most vulnerable to predators in the egg, larval, and fry stages. In order to minimize the impact of predation, milkfish produce large amounts of eggs in deep water (Bagarinao 1994). (Bagarinao, 1994; Villaluz, 1990)

Ecosystem Roles

Not much is known about the effects that milkfish have on the ecosystem. They are important as both predators and prey of other fish species and of coastal planktonic communities. (Bagarinao, 1994)

Economic Importance for Humans: Positive

Milkfish are commercially raised for food in the Philippines and Indonesia (Gale 2003). More than a quarter of a million tons of milkfish are harvested every year in brackish ponds in Indonesia, Taiwan, and the Philippines. These fish contribute around 60% of the total fish production from aquaculture in Southeast Asia (Garcia 1990). ("Milkfish Chanos chanos", 2003; Garcia, 1990)

  • Positive Impacts
  • food

Economic Importance for Humans: Negative

There are no known adverse effects of Chanos chanos on humans.

Conservation Status

Chanos chanos populations seem to be stable, this species is not listed on any conservation registry.

Contributors

Tanya Dewey (editor), Animal Diversity Web.

Joelle Sarroca (author), University of Michigan-Ann Arbor, Kevin Wehrly (editor, instructor), University of Michigan-Ann Arbor.

Glossary

Pacific Ocean

body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

brackish water

areas with salty water, usually in coastal marshes and estuaries.

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

detritus

particles of organic material from dead and decomposing organisms. Detritus is the result of the activity of decomposers (organisms that decompose organic material).

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

external fertilization

fertilization takes place outside the female's body

fertilization

union of egg and spermatozoan

food

A substance that provides both nutrients and energy to a living thing.

freshwater

mainly lives in water that is not salty.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

metamorphosis

A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

omnivore

an animal that mainly eats all kinds of things, including plants and animals

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

pheromones

chemicals released into air or water that are detected by and responded to by other animals of the same species

reef

structure produced by the calcium carbonate skeletons of coral polyps (Class Anthozoa). Coral reefs are found in warm, shallow oceans with low nutrient availability. They form the basis for rich communities of other invertebrates, plants, fish, and protists. The polyps live only on the reef surface. Because they depend on symbiotic photosynthetic algae, zooxanthellae, they cannot live where light does not penetrate.

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

social

associates with others of its species; forms social groups.

tactile

uses touch to communicate

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

visual

uses sight to communicate

zooplankton

animal constituent of plankton; mainly small crustaceans and fish larvae. (Compare to phytoplankton.)

References

Gale Group. 2003. Milkfish Chanos chanos. Pp. 293 in M Hutchins, D Thoney, P Loiselle, N Schlager, eds. Grizimek's Animal Life Encyclopedia, Vol. 4, 2nd Edition Edition. Farmington Hills, MI: Schlager Group, Inc..

Bagarinao, T. 1994. Systematics, distribution, genetics and life history of milkfish, Chanos chanos. Environmental Biology of Fishes, 39: 23-41.

Doving, K. 2000. "B. Chemosensory function" (On-line). Accessed October 10, 2005 at http://biologi.uio.no/genfys/groups/GN/pro_b.html.

Garcia, L. 1990. Fishery Biology of Milkfish (Chanos chanos Forskal). Proceedings of the Regional Workshop on Milkfish Culture Development in the South Pacific. Accessed October 10, 2005 at http://www.fao.org/docrep/field/003/AC282E/AC282E04.htm#ch3.2.

Villaluz, A. 1990. Milkfish Fry Collection and Handling. Proceedings of the Regional Workshop on Milkfish Culture Development in the South Pacific. Accessed October 10, 2005 at http://www.fao.org/docrep/field/003/AC282E/AC282E04.htm#ch3.3.

Villaluz, A., A. Unggui. 1983. Effects of Temperature on Behavior, Growth, Development and Survival in Young Milkfish, Chanos chanos (Forskal). Aquaculture, 35: 321-330. Accessed October 10, 2005 at http://www.sciencedirect.com.proxy.lib.umich.edu/science?_ob=MImg&_imagekey=B6T4D-49NPHW6-KB-6&_cdi=4972&_user=99318&_orig=browse&_coverDate=12%2F31%2F1983&_sk=999649999&view=c&wchp=dGLbVzb-zSkWA&md5=b7cd10f6f4f24a246fe5c83dfdc8e814&ie=/sdarticle.pdf.