Expert topic: Milkfish
by Matthew Holmes, Features Editor, International Aquafeed
The Milkfish (Chanos Chanos) is the national fish of the Philippines, referred to locally as the ibiya. They dwell primarilyin the Indian Ocean, but are also present in the Pacific Ocean,from South Africa to Hawaii and the Marquesas, from California to the Galapagos, north to Japan and south to Australia.
Milkfish commonly live in tropical offshore marine watersaround islands and along continental shelves, at depths of between 1-30m. They also frequently enter estuaries and rivers.They are stenothermic fish, so therefore if you farm them in fish farms, they must be kept within extremely specific temperatures,otherwise they will fall ill and die.
The milkfish can grow to 1.80m (5 ft 11in) but are often nomore than one metre (39in) in length. They can reach a weight of approximately 14kg and can live up to an impressive 15 years.Milkfish have elongated bodies, with a generally symmetrical and streamlined appearance with one dorsal fin, falcate pectoral fins and a sizable forked caudal fin, which assists the milkfish insteering and swimming.
Their mouth is small and toothless, and their body a pale olivegreen, with silvery flanks and dark bordered fins.
Considered to be iliophagous, (a fish that gains its nutrients from eating decomposing plant and animal parts), milkfish ingest the various micro- and meiofauna found on the ocean floor. They can also be weaned onto artificial feed, provided they are fed this within the first two-to-eight-days of hatching.
Milkfish tend to school around coasts and islands amongst coralreefs. The young fry live at sea for two to four weeks beforemigrating during the juvenile stage, (also called fingerlings), to mangrove swamps, estuaries, and sometimes lakes.
The reproductive cycle of the milkfish still remains relatively unknown. Their reproductive cycles have, however, been studied and are believed to be largely influenced by the lunar cycle and can often take place multiple times in a year, usually at night. Milkfish return to the sea to mature sexually and reproduce, when they reach between three and 15 years old.
Females spawn at night between 0.5 and six million eggs in saline shallow waters, which take between 20 and 35 hours to hatch. Once born, the larvae are about 3.5mm in length, andrely solely on their yolk for nutrients for their first five days of existence.
A Philipine tradition
The milkfish is an important seafood in Southeast Asia and some Pacific Islands. Because milkfish is notorious for being much bonier than otherculinary fish, deboned milkfish, also called boneless bangús in the Philippines, has become increasingly more popular in stores and markets.
Milkfish aquaculture first occurred around 800 years ago in the Philippines and spread in Indonesia, Taiwan, and into the Pacific. Traditional milkfishaquaculture relied upon restocking ponds by collecting wild fry. This led to a wide range of variability in quality and quantity between seasons and regions.
In the late 1970s, farmers first successfully spawned breeding fish. However, these were difficult to obtain and produced unreliable egg viability. In 1980, the first spontaneous spawninghappened in sea cages, whose eggs were then found to besufficient to generate a constant supply for farms.
Fry are raised in either sea cages, large saline ponds orconcrete tanks. Milkfish reach sexual maturity at 1.5kg (3.3lb), which takes five years in floating sea cages, but eight to tenyears in ponds and tanks. Once they reach 6kg (13lb), 3–4 million eggs are produced each breeding cycle. This is mainly done using natural environmental cues. However, attempts have been made using gonadotropin-releasing hormone analogue (GnRH-A) to induce spawning.
Some still use the traditional wild stock method, which is capturing wild fry using nets. Milkfish hatcheries,
like most hatcheries, contain a variety of cultures, for example, rotifers, green algae, and brine shrimp, as well as the target species.
They can either be intensive or semi-intensive. Semi-intensivemethods are more profitable at £5.20 per thousand fry in 1998,compared with £21.34 for intensive methods. However, the experience required by labour for semi-intensive hatcheries is higher than intensive.
Pond culture, pen culture and cage culture
Milkfish nurseries in Taiwan are highly commercial and have densities of about 2000/L. Indonesia achieves similar densities but has more backyard-type nurseries. The Philippines has integrated nurseries with grow-out facilities and densities of about 1000/L. The three methods of outgrowing are pond culture, pen culture, and cage culture, which all have their own advantages and disadvantages:
Shallow ponds are found mainly in Indonesia and thePhilippines. These are superficial (30–40 centimetres), brackishponds ripe with benthic algae which is usually used as feed. These are usually excavated from nipa or mangrove areas and produce about 800 kg/ha/yr. Deep ponds (2–3 m) have morestable environments and their use in milkfish production began in 1970. So far, milkfish farmed in this manner have shown less susceptibility to disease than shallow ponds.
In 1979, pen culture was introduced in Laguna de Bay, which had high primary production. This provided an excellent food source. Once this ran out, fertilizer was applied. They are susceptible to disease.
Cage culture usually occurs in coastal bays. These consist of large cages suspended in open water. They rely largely on natural sources of food present in the water. In the Phillipines especially,stocking rates via cage culture are very high, from five up to 30/m3.
Due to the milkfish"s sensitivity to temperatures and water conditions, they have sometimes proven difficult to effectively farm and are for. These fish once were caught as fry, and raisedinto adulthood, but this often came with heavy losses, many ofthe milkfish dying as fingerlings. The unpredictability of theocean waters has meant that farmers must now monitor theirmilkfish exceedingly carefully.
The past decade has seen a improvement in the monitoring ofmilkfish and mortality rate, thanks to the production of privatehatcheries, research institutions and government agencies. Manyof the milkfish fry used now in farming in the Philippines, Chinaand Indonesia come from specialised hatcheries. Despite thesesuccesses though, milkfish survival rate in hatcheries still remainsat only a minimal 30 percent.
An impressive future ahead
As milkfish production only continues to gain in popularity, the expected figures of production and sales have increased drastically. In 2005, the supply of milkfish was approximately79,000 tonnes, which reached an impressive 369,000 tonnes in 2010.
These numbers are still only continuing to increase,despite milkfish being largely considered, in the Philippines, asa meal younger generations dislike for its bony texture. As The General Agreement on Tariffs and Trade (GATT) begin to add trade restrictions and quality control standards to the productionof milkfish, it has been foreseen that milkfish production willdrastically increase in price. Yet, despite this, the future formilkfish still remains positive, as the demand only continues to grow.