Production

Production Cycle

Production systems

Seed supply

Milkfish fry can either be obtained through collection from coastal areas or littoral waters or can be produced in captivity. The supply of wild fry is often unpredictable; catches in recent years have diminished and cannot satisfy the demand from ongrowing farms. 

Fry from captive broodstock and spawners 

To develop broodstock under captive conditions, large juvenile milkfish may be stocked, fed and maintained in floating sea cages in protected coves or in large, deep, fully saline ponds (as practiced in the Philippines), or in large deep concrete tanks on land (as practiced in Indonesia and Taiwan Province of China), until they reach sexual maturity with an average body weight of at least 1.5 kg. Land-based broodstock facilities are entirely dependent on fresh pumped seawater supplies and are often integrated with a hatchery. 

Broodstocks reach maturity in five years in large floating cages, but may take 8-10 years in ponds and concrete tanks. On average, first-spawning broodstocks tend to be smaller than adults caught from the wild. As a result, first-time spawners produce fewer eggs than wild adults, but larger and older broodstocks produce as many eggs as wild adults of similar size. Broodstocks of about 8 years old and averaging 6 kg produce 3-4 million eggs. 

Breeding milkfish in captive conditions and the mass production of fry, as practised in Taiwan Province of China, Indonesia and the Philippines, is mostly dependent on natural spawning, which assures high survival rates. Artificial induction is not normally used. On days when natural spawning occurs, the fish may feed less than usual but show increased swimming activity and exhibit chasing, occasional leaping, and water-slapping activities from late noon to early evening. Spawning usually takes place around midnight but daytime spawning sometimes occurs. 

Wild-caught fry 

Wild-caught fry are collected with fine-mesh seines and bag nets of various indigenous designs in the Philippines, Taiwan Province of China and Indonesia. The most commonly used gear are push net 'sweepers' and dragged seines.

Hatchery production

Milkfish hatcheries consist of larval rearing tanks, culture tanks for rotifers (Brachionus) and green algae (e.g. Chlorella) and hatching tanks for brine shrimp (Artemia). Larval rearing may be either operated in outdoor or indoor systems, depending on the specific conditions in the countries where fry are being produced. 

Hatchery operations utilise either intensive (high stocking density, high volume tanks, daily feeding and water exchange) or semi-intensive (low stocking density, high volume tanks, minimal water exchange, feeding with mixed diet) systems, with an average survival rate of 30 percent (from stocked newly-hatched larvae). After hatching, the larvae are ideally kept at 50/litre in hatchery tanks (either concrete, fibreglass, canvas or polypropylene-covered earthen tanks) maintained with Chlorella and fed with rotifers during the early stages

and later with copepods or brine shrimp for a total of 3-4 weeks. Following this, their size ranges between 2-3 cm and they are ready for transport to nurseries. 

The fry may change hands two or more times before being used for grow-out; each time this happens, they are sorted and counted, transported, and stored for different periods of time. Fry are a highly perishable commodity and some of them die during gathering, storage, transport, nursery rearing and grow-out. The technologies for fry storage and transport are generally effective, although perhaps not yet optimised. Fry are stored in a cool place in plastic basins or clay pots at 100-500/litre, in water of 10-25 per cent, which is renewed daily. Dealers may store fry for 1-7 days, depending on the demand. Fry can be maintained on wheat flour or cooked chicken egg yolk for 1-2 weeks but soon begin to die, despite continued feeding. Recently, micro-encapsulated feeds have become commercially available for finfish but the cost compared to conventional live feeds is higher.

Nursery

Nursery operations in milkfish producing countries vary according to established cultural practices. 

In Taiwan Province of China, where commercial hatchery and nursery productions are integrated enterprises, milkfish fry are generally grown in either earthen ponds or elevated canvas or concrete tanks at intensive stocking densities of >2 000/litre. 

In Indonesia, a well established backyard-type nursery is used. This consists of a series of elevated canvas or concrete 1-2 tonnes tanks and similar stocking densities to those used in Taiwan Province of China are employed. 

In the Philippines, milkfish nurseries are integrated with grow-out facilities, where wild-caught or hatchery-reared fry are first acclimated into nursery compartments which comprise one third to one quarter of the total area of the Brackish water pond. Fry are stocked at a density of up to 1 000/litre and are fed with a naturally-grown micro-benthic food known as 'lab-lab' which grows on the fertilised pond bottom. Nursery rearing has also been carried out in hapa type suspended nylon nets installed in Brackish water ponds or lagoons and in freshwater lakes within the grow-out compartments, a traditionally practice in the Philippines. When natural food is becoming depleted, artificial feeds such as rice bran, corn bran, and stale bread or formulated feeds are provided. In about 4-6 weeks, the fry grow to 5-8 cm juveniles, which is the ideal size for releasing into grow-out ponds or pens. Depending on the desired grow-out period, juveniles or fingerling size milkfish are kept in nurseries or transition holding tanks up to the required stocking size of 30-40 g. Nursery rearing from fry to fingerling size normally achieves 70 percent survival.

Ongrowing techniques

Milkfish may be ongrown in ponds, pens or cages. Pond culture

Culture of milkfish in ponds may be in shallow or deep water systems.

Shallow water culture is practiced mainly in Indonesia and the Philippines. Milkfish are traditionally cultured in shallow Brackish water ponds in which the growth of benthic algae is encouraged through inorganic or organic fertilisation. Milkfish will survive on benthic algae alone only if the productivity of the algae exceeds the grazing rate of the fish; otherwise, supplemental commercial feeds are applied. The 'lab-lab' culture system in the Philippines is equivalent to shallow water culture in Taiwan Province of China. 'Lab-lab' is the term used in this

country for the algal mat (and all micro-organisms associated with it) in the ongrowing ponds.

Brackish water ponds in the Philippines were mostly excavated from 'nipa' and mangrove areas. Shallow water pond design generally consists of several nursery and production ponds with a typical area of 2 000 m² for nursery ponds and 4 ha for production (ongrowing) ponds. Typically, ponds have a depth of 30-40 cm and are provided with independent water supplies. 

The average yield of a typical integrated nursery, transition and shallow grow-out system that produces 3 crops a year is 800 kg/ha. Modified modular pond designs consisting of a series of grow-out compartments with a maximum of eight crops a year have been shown to increase yield to a high as 2 000 kg/ha. 

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. Deep-water ponds provide a more stable environment and extend the grow-out period into the winter season. Most deep-water milkfish ponds have been created by converting either shallow water ponds or freshwater ponds, with a depth of 2-3 m. Production from these systems has sharply increased in Taiwan Province of China, having expanded from 23 percent of the total production in 1981 to 75 per cent in 1990. 

Most milkfish ponds in the Philippines and Indonesia are of the extensive and semi-intensive type, with large shallow pond units, tidal water exchange, natural food, minimal use of fertiliser alternating with commercial feeds and other inputs, and low to medium stocking rates (50 000-100 000/ha). The Taiwanese method of production, on the other hand, employs intensive stocking densities (150 000-200 000/ha). Few diseases or infestations have been recorded so far in milkfish grow-out farming in these Asian countries. 

Pen culture 

This system was introduced in the Philippines in 1979 in the 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 exceeded more than 50 percent of the total lake surface, which is 90 000 ha. As the primary production of the lake could not meet this sudden expansion of aquaculture, and feeding became necessary to meet the nutritional requirements of the cultured fish, the pen culture practices developed in lakes were later introduced into inter-tidal areas in the Philippines along coves and river estuaries as well. Pen operators stock fingerlings at 30 000-35 000/ha and provide supplemental commercial diets. However, disease spreads among culture pens and causes mass mortality. Government regulations are now being considered to maintain sustainable yields from this type of farming. 

Cage culture 

Fish cages are smaller and more restricted enclosures that can be staked in shallow waters or set-up in deep water with appropriate floats and anchors. Cage farming of milkfish is commonly carried out in marine waters along coastal bays. Stocking rates (in the Philippines) are quite high, from 5 up to 30/m³.

Feed supply

In the past, traditional feeding practices for milkfish grow-out production have consisted of natural food ('lab-lab') or a combination of phytoplankton and macroalgae (Enteromorpha intestinales, Cladophora spp. or

Chaetomorpha linnum) encouraged by fertilisation. In the 1980s however, special commercial feeds for milkfish were developed and became almost exclusively used. As cage and pen culture technology proliferated in the 1990s, both in marine and inland waters, extruded milkfish feeds were further developed into floating and semi-floating forms, while sinking forms were used for pond and tank-based grow-out. Feed supplies are now manufactured commercially in the form of starters, growers and finishers, which are administered according to the production stage of the milkfish.

Harvesting techniques

Milkfish are normally harvested at sizes of 20-40 cm (about 250-500 g). There are three known methods used for harvesting milkfish:

Partial harvest. Selective harvest of uniformly grown milkfish from grow-out facilities (i.e. cages, pens, ponds, tanks) using seine or gillnets, retaining the undersize fish and harvesting only the commercial sized stocks, with an average body weight of 250 g or larger. 

Total harvest. Complete harvest in one crop period from grow-out facilities (i.e. total draining of ponds by gravity or pump, hauling of the entire net cage structure, seining or the use of gillnets in pens). The harvest size at this stage may vary from 250-500 g. 

Forced harvest. Emergency harvesting, regardless of fish size or grow-out stage, which is carried out during 'fish kills' due to oxygen depletions that are attributed to algal blooms, red tide occurrence, pollution or other environmental causes.

Handling and processing

200-400 g milkfish are harvested and marketed mostly fresh or chilled, whole or deboned, frozen, or processed (e.g. fresh frozen deboned, fresh frozen deboned descaled, and smoked fish deboned). In general, all marketed milkfish are produced in farms, only a few being caught from natural waters. In some countries (e.g. the Philippines) fishing for adult milkfish is officially banned in order to protect the natural broodstocks. 

There are two known post-harvest processing techniques for milkfish, which are the traditional (i.e. drying, fermentation and smoking) or non-traditional methods (i.e. bottling, canning and freezing) and value-added products such as 'surimi' and deboned products as practiced in Taiwan Province of China and in the Philippines. 

Regulations and standard protocols for manufacturing milkfish products exist for both domestic consumption and export, as follows:

Good Manufacturing Practices (GMPs). Plant construction. Personnel hygiene and sanitation. Standard Sanitary Operating Procedures (SSOPs). HACCP compliance.

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