Milkfish frySeptember 21, 2009
Chanos chanos is the only species in the family Chanidae.
Common Names: USA: milkfish; Japan: Sabahii; Central Taiwan: Masaba; South Taiwan: Hi Tsu Hii; China: Su Mu Yii; Philippines: Sabalo, Bangus (Tagalog), Hawaii: Pua Awa, Awa. Indonesia: Bandeng, Bolu.
Special Features: The milkfish is an unusual fish. It is anatomically unusual. It is unusual with respect to its evolutionary position and relationships. It is unusual in both its extremely wide geographic distribution and its ability to tolerate, even to thrive under, very wide ranges of environmental conditions. It is unusual in its life history which is in large part the basis for its suitability as a farm animal.
Milkfish distribution is restricted to either low latitude tropics or the subtropical northern hemisphere. Milkfish spawning is highly variable and depends from the location of appearance. Spawning activity most often is correlated with new- as well as full moon phases, takes place mostly in the night and in most regions with one or two seasonal peaks (April – July, September – November).
Milkfish is a heterosexual fish. Hermaphroditism in this fish has not been reported. Sex ratio is nearly equal with slightly higher amount of females in natural spawned stocks. Determination of sex is very difficult, because there are no easily identifiable morphological differences between males and females.
The pheromone PGF2a (Prostaglandine) was found to be an effective way to identify mature male milkfish.
History of use:
The milkfish is one of the most extensively farmed marine bony fishes on earth. Despite its extensive culture, milkfish remains one of the least well known and understood of the major finfish species.
Pond culture of the milkfish dates back to about 700 years ago in Indonesia to at least 400 years ago in Taiwan and the Philippines and probably to at least 300 years ago in Hawaii. Culture methods in a variety of water bodies are constantly being improved upon. As a widely eaten and widely farmed fish, the milkfish is well known to people in many different countries.
In 1984, milkfish ponds in three major milkfish farming countries (Taiwan, the Philippines and Indonesia) more then 391,000 ha yielded an annual productionof 352,643 Metric tonnes.
Milkfish fry fishery is unique among the renewable aquatic ressources. Here is the larvae that are exploited and therefore, the common methods of stock assessment in predicting the future of the fishery cannot be adopted.
The prime market size for milkfish throughout most of the Far East is about 300 – 400 grams, meaning fish usually is less than one year old. Milkfish do not reach sexual maturity, however, until 5 – 7 years of age. Thus milkfish farming has been a traditonal industry with little emphasis on producing sexually mature, reproductively active fish in captivity. The traditional milkfish industry was depending totally on an annual restocking of farm ponds with fingerlings grown up from wild-caught fry. As a result, the industry was suffering from regional, saesonal and annual variations in fry availability. These variations are generally unpredictable, and may be quite large over short periods of time. Thus, the central problem faced by the international milkfish industry was to find a way to produce a reliable, adequate, high quality supply of milkfish fry that was not subject to large unpredictable variations in time and space.
During the past decade, much progress has been made, particularly in regards to milkfish propagation, by private hatcheries and research institutions. Instead of relying on wild-caught fry, milkfish farming in Taiwan now obtains the majority of fry from the hatchery. This is mainly due to the significant shortage of natural caught fry in this country. Milkfish fry production is also developed in Indonesia and the Philippines.
Since 1985, hatchery produced milkfish fry have been over one million. The total production from hatcheries was 6.2 million in 1985, rapidly increasing to 130 million in 1990 and 116 million in 1991. Hatchery production accounted for 74.5% of the total fry supply in 1990 and 86.1% in 1991. Between 1975 and 1990, the total supply of milkfish fry showed an annual increase rate of 4.14%.
Partially (28%), milkfish farming is polycultured with other species, the unit production of milkfish from a polyculture system was lower than from monoculture systems.
Combined total annual milkfish production in the most important countries for milkfish production such as Taiwan, the Philippines and Indonesia has exceeded 300,000 Metric tonnes since 1980 and shows a general trend of increasing.
In more detail, milkfish culture production from the Philippines from 1975 to 1990 fluctuated between 106,000 MT (1975) and 210,000 MT (1990) with a production peek of 238,000 MT in 1983 (more details? Availaible! Curves?).
In Indonesia, milkfish culture production from 1976-1990 was increasing from 44,000 MT up to 138,000 MT. In Taiwan, milkfish production from 1975 to 1990 was variing between 19,000 MT (1980) and 90,000 MT (1990).
Production rates vary between 7,000 and 8,100 kg/ha (Taiwan, polyculture and monoculture respectively), 700-1,000 MT (Philippines, polyculture and monoculture respectively) and 320-750 MT (Indonesia, polyculture and monoculture respectively).
Milkfish distribution is restricted to either low latitude tropics or the subtropical northern hemisphere. Mainly farmed in Taiwan, Philippines, Indonesia and Hawaiian Islands.
Climate and Environmental Tolerance
Milkfish is remarkably euryhaline. Except during spawning and the early larval stages, they can be found from freshwater lakes to hypersaline lagoons. In brackishwater ponds, wide salinity fluctuations usually occur during the growing season. The salinity tolerance range during 48h exposure periods is 4-38psu for very young milkfish and 0-70psu for 21-days old larvae. Fingerlings tolerate abrupt changes in salinity as long as the change is not direct to freshwater. Temperature tolerance is 14-18°C for lowest and 38-41°C for the highest limit in juvenile milkfish.
Lethal oxygen limit for juvenile milkfish is 0.1-0.3 ppm.
Ammonia and nitrite level: for milkfish fry, the lethal level (96-h LC50 ) is 28-30 ppm, values far above the 0-6ppm ammonia seen in ponds. For juvenile milkfish (2-4g), the 96h-LC50 concentration is 21ppm.
The optimum acidity is pH8, the normal pH of seawater. Low survival was obtained for fry after 96h exposition to pH 5.
Properties of milkfish larvae:
Newly hatched larvae measure 3.5mm TL at hatching have large yolk sac volume (0.5µl) unpigmented eyes and no mouth. They grow to about 5mm in 36h, consuming 90% of the yolk and grow very little until day 5 when the yolk is completely exhausted. Egg size, larval size, amount of yolk and mouth size are greater in milkfish than in many other tropical marine fishes (such as sea bass Latis calcarifer and the rabbitfish Siganus guttatus). This size advantage is probably one reason for the relative ease in rearing milkfish larvae in the hatchery and for the abundance of milkfish fry in the wild.
For ecological studies, the larval periode may be broken down into 5 stages based on morphological and behavioral characteristics following the system of Kendall et al. (1986). Measurements for larvae in the plankton samples, preserved and for larvae reared in the laboratory and measured in the fresh state (in parentheses).
Stage 1: Yolk-sac larvae: TL 3.3-4.4mm (3.2-5.4mm), stage lasts 3 d.
Stage 2: Pre-flexion larvae: TL 3.4-5.6mm (5.0-6.3mm), stage lasts 5 d.
Stage 3: Flexion-larvae: TL 4.4-9.9mm (5.4-10.0m), stage lasts 6 d.
Stage 4: Post-flexion larvae or fry: TL 9.5-16.5mm (6.4-14.9mm), stage lasts 7 d.
Stage 5: Transformation larvae: TL 9.5-16.5mm (6.4-14.9mm), stage lasts 2-4 weeks.
Apparently there is a mechanism that enables milkfish larvae to come to shore waters from open water spawning grounds, and only the larvae that have attained a certain degree of morphological, physiological and behavioral development (probably 10mm and 2 weeks old) are able to utilize such mechanism. Contrary to popular belief, milkfish fry do not seek freshwater habitats. Rather they seek habitats with abundant food, which in the tropic happen to be mainly mangroves-vegetated brackish water coastal wetlands.
Milkfish fry are phemonenally abundant. Total catch potentials are not known but some 1.35 billion fry were collected in the Philippines in 1974 and 700-800 million fry are collected in Indonesia per year. Taiwan which has far less coastline collected an average 30 million fry a year during the periode before 1945 and 130 million of fry after 1950. These fry go into a grow-out culture industry that produces 285 000t of milkfish a year in southeast Asia.
Feeding of larvae, juveniles and adults:
Larvae and fry
Feeding commences shortly after the eyes become fully pigmented and the mouth opens (54h from hatching) and before the yolk is completely resorbed (120h). Unfed larvae all die about 150h from hatching at rearing temperatures of 25-27°C. Larvae are particulate visual feeders and small live prey such as rotifers (Brachionus) water flee (Moina) harpacticoid copepod (Tisibintra) and brine shrimp (Artemia) have been successful used as feed for rearing milkfish larvae and fry. When milkfish larvae are about 2 weeks old, they begin to be able to take non-live feed; about 40% can be weaned to the juvenile stage using various finely ground artificial diets.
Juvenile milkfish take food mainly from the bottom. The kinds of food ingested vary by habitat and fish size. Juveniles from natural habitats feed mainly on cyanobacteria, diatoms, detritus along with filamentous green algae and invertebrates such as small crustaceans and worms. The food items of juvenile milkfish in culture ponds are very similar to those in natural environment but depends on the availability of food.
Milkfish is characterized as being iliophagous, ingesting the top layer of bottom sediments with the associated micro- and meiofauna, as mullets do. A great deal of this material is detritus which is rich in protein due to its high complement of bacteria, fungi, and protozoans and has been shown to be important in tropical shallow-water food chains. Detritus is probably utilized by juvenile milkfish as soon as they reach their depositional-type habitats.
Both planctonic and benthic plants and animals occur in the guts of adult milkfish. Large quantities of zooplankton and larval and juvenile clupeoids were found in the gut of adult milkfish. There is usually 1- 2 kind of food in a gut, suggesting that adult milkfish feed by swimming through plankton masses or larval fish schools. Adults are also reported to graze on rock surfaces and on floating algae. Thus adult milkfish, like the juveniles, are opportunistic generalists. Adult milkfish can be kept in captivity on a diet of commercial pellets with about 42% protein given at 1.5-2% of body weight twice daily. Adults can take pellets from a feeding tray both day and night, but more actively during the day.
Current farming methods
Milkfish fry can either be supplied by natural grown larvae collected in coastal areas or littoral waters or can be produced in captivity. The supply of wild fry is often unpredictible and catches in recent years has apparently diminished and cannot satisfy the demand for fry for ongrowing farms. Thus, hatchery production will stabilize more and more the supply of fry and can promote increased production of milkfish. For optimal and successful operation of artificial propagation, a healthy mature broodstock is necessary. Although less efficient, wild broodstock can be collected.
Milkfish hatcheries needs larval rearing tanks, culture tanks for rotifers (Brachionus spec.) and green algae (e.g. Chlorella) and hatching tanks for brine shrimps (Artemia). Larval rearing procedures can be either operated in outdoor or indoor systems, depending from special conditions in the countries where milkfish fry is being produced.
Before milkfish fry are stocked in grow-out ponds, they are usually kept in small compartiments which are in junction with growout ponds in order to recover from transport stress or to be acclimated to new culture environments. When natural food is depleting, artificial feeds such as rice bran, corn bran, stale bread or formulated feed are supplemented. In about 4-6 weeks, the fry grow to 5-8 cm which is the ideal size for releasing in grow-out ponds or pens.
Ongrowing methods are in general operated in three different systems:
i) shallow water culture: practised mainly in Taiwan. Milkfish are traditionally cultured in shallow, brackish water ponds in which the growth of benthic algae is encouraged through fertilization of the ponds. Milkfish will survive on benthic algae alone only if the productivity of the algae exceeds the grazing rate of the fish, otherwise, supplemental feed is required.
The “lab-lab” culture system on the Philippines is equivalent to shallow water culture in Taiwan. “Lab-lab” is the term used in the Philippines for the algal mat and all micro-organisms associated with it in the ongrowing ponds.
Shallow water pond design in general is as following: the system includes several nursery and production ponds with a typical area of 2000m² for nursery ponds and 4ha for production (on-gowing) ponds. The ponds typical have a depth of 30-40cm and are connected by passageways.
The average yield of ordinary shallow water culture with 3 crops a year is 800kg/ha. The modular pond technique with a maximum of eight crops a year increases the yield up to 2000k/ha.
ii) deep water culture: was developed in the mid 1970s in response to the decline of profitability of shallow water culture, and the limited and increasing value of land and manpower resources. The deep-water pond provides a more stable environment and extends the milkfish growing into winter season. Most of deep-water milkfish ponds have been created by converting either shallow water ponds or freshwater ponds, with a depth of 2-3m. Production from this system has sharply increased in Taiwan, representing 23% of the total production in 1981 75% (or 68,037t) in 1990.
iii) pen culture: was introduced in the Philippines in 1979 in Laguna Lake. At that time, the lake had a very high primary productivity, which met the nutritional needs of milkfish. Because of the low rate of input and the high rate of return, the pen culture area increased sharply from 1973 to 1983, and culture areas exceeded more than 50% of the total lake surface which is 90,000ha. As a result, the primary production of the lake could not meet the sudden expansion of milkfish culture, and feeding became necessary to meet the nutritional reqirements of the cultured fish. Furthermore, disease spread among culture pens and causes mass mortality. Government regulations are now being considered to mainatin sustainable yields from this type of farming.
Processing and Marketing
Although adult milkfish can reach sizes of 120cm and weights of about 10kg, fish is harvested with a size of 20-40cm (about 200-400g). In general, all market milkfish is produced in farms, only few catches are reported from natural waters. In some countries (e.g. Philippines) fishing for adult milkfish is officially banned in order to protect the natural broodstocks.
In the Philippines, Taiwan and Indonesia milkfish is sold fresh, frozen, or processed (e.g. fresh frozen deboned, fresh frozen deboned descaled, and smoked fish deboned). Producers of milkfish do not usually sell fish directly to consumers, but instead deliver fish through cooperatives, brokers, dealers, collectors or wholesalers, and retailers. In general, the majority of fish products are sold in auction markets through dealers, brokers, wholesalers or cooperatives to smaller dealers, and then retailers.
Milkfish price and personal income affect the amount of milkfish consumed in the countries of origin. Studies conducted in Taiwan and the Philippines concluded that own price and income elasticities of demand for milkfish had a negative and positive elasticity coefficient, respectively.
Likely future trends
The introduction of milkfish hatchery technology had a positive net economic impact on output, employment, and income, including the anticipated negative impact on the wild fry collectors sectors. Both producers and consumers benefit from this new technology. However, the technology for induction of spawning or induction of off.season maturation is still unreliable (this was the situation in 1995) with more research required before the fry supply schedule can be fully controlled. Because milkfish fry constituted major cost item in production, the overall production cost will decrease as fry cost decreases.
The impacts of technical development and socioeconomic change in milkfish farming are mentioned below:
i) Traditional food fish
Milkfish has been a traditional food fish in Taiwan, the Philippines and Indonesia fore more than 400 years and will remain in the future. Improvements to the transportation system allows milkfish to be delivered to previously unreachable areas, thus expanding existing markets. However, the younger generation in the existing market tends to avoid eating milkfish because of their bony flesh (they prefer obviously Mc Donalds….), thus new markets for milkfish will be difficult to initiate.
ii) Less farming area, higher unit production
Due to the high value of of land and relative low value of milkfish, milkfish farmers have to introduce new technology to improve production for the same unit area (e.g. module pond technique, deep-water culture). In the future milkfish will no longer rely only on the natural productivity of the ponds and will instead be fed formulated feed.
iii) Stable supply of milkfish fry
Hatcheries started to provide reliable sources of fry and it is anticipated that in the near future more hatcheries, especially in Taiwan and Indonesia, will produce milkfish fry to further lower fry price and stabilize supply. Current fry production technology has relied mainly on natural spawning of milkfish during spawning season, advanced techniques to overcome this problem will decrease production costs of milkfish because of decreasing costs for milkfish fry.
iv)Expansion of milkfish market
Milkfish is sold in either fresh or frozen form and is accepted by limited markets due to its bony flesh. To overcome this problem, milkfish is also marketed in boneless form and in cans. At this time, canned milkfish is not cost-effective, but this situation will improve as production efficiency increases. Additional, other milkfish forms need to be developed in order to increase acceptance of different ethnic groups., Finally new products require advertisement if they are to be successfully marketed.
Milkfish are also good bait for tuna fishing and the the marketing of bait fish is underdeveloped because of the restricted availability and cost of milkfish fingerlings. As mass production of milkfish fry in the hatcheries expands, more fingerlings will also become availaible for the bait fish industry.
Milkfish has been farmed for more than 400 years and will continue to be a desired species. Previous research first focused on grow-out technology, followed by fry production technology. Completion of the milkfish live cycle in captivity has made milkfish farming more controllable. Expansion of the milkfish market beyond curent markets will require research and development on the marketing and processing of milkfish.
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source from : http://www.larvalbase.org/MiniEssay.htm