Aquavetplan enterprise Manual Version 0, 2015

B3.4 Prawn hatcheries

Production of post-larval prawns for stocking into grow-out ponds requires collection of broodstock from the wild. Research is in progress to domesticate prawns so that the full life cycle can be grown in captivity, and this represents the trend for the future. P. monodon, P. japonicus, P. esculentus and F. merguiensis have been successfully domesticated in Australia, and other species of prawn have been bred domestically overseas. Some problems with fecundity of domesticated stock still need to be overcome before it can fully replace the wild-caught alternative.

B3.4.1 Practices

Broodstock caught from the wild or grown in farm ponds is moved to maturation tanks in the hatchery. Since the animals can only mate during moult when the female’s shell is soft, most hatchery operators prefer to receive gravid or berried broodstock from the wild, where fertilisation has already taken place.

The broodstock, if ripe and ready to spawn, is placed in a spawning tank, and her eggs are collected after she spawns. If the broodstock is not fully gravid, she is ablated (one eyestalk is removed), thus accelerating the spawning process. Eggs are collected, rinsed and washed, sometimes in a weak solution of formalin or iodine to clean the eggs and reduce the potential for vertical transmission of disease. The eggs are usually counted, and then placed in hatching tanks.

When the eggs hatch, they go through six stages of nauplius development and metamorphosis. Before the sixth stage, they are usually moved to larger tanks of sea water. In these tanks, the animals progress through three zoea stages and three mysis stages before metamorphosing to post-larval prawns.

The young prawns are usually kept in the hatchery until they reach 15 days of age and are then sold to grow-out farms for culture. The entire process from egg to post-larvae (15 days of age) takes normally about 25 days, but can be longer in the cooler winter months.

B3.4.2 Premises and equipment

Facilities differ but have similar basic needs, both in Australia and overseas. Hatcheries come in various sizes; the volume of tanks in the hatchery depends on the number of post-larval animals that the owner or operator plans to produce. Large commercial hatcheries may produce 60–100 million post-larval prawns per year, whereas others produce 20 million or fewer.

Generally, hatcheries include a building to house the various tanks required for maturation, spawning, hatching, larval rearing, grow-out and algae production. Ancillary support equipment includes pumps to take water from the sea or estuary, settlement ponds, reservoir tanks, heating equipment such as boilers to maintain water temperature, filtration devices, ozone disinfection units, UV flow-through devices to eliminate bacteria in the water column, a food storage area, and a small laboratory and office.

B3.4.3 System inputs

Broodstock

Animals are usually purchased from prawn trawlers and placed in maturation tanks. Some are produced in maturation ponds and are second or third generation. Wild broodstock carry covert viral infections that can become problematic in an intensive farm situation because they can be vertically transmitted to larvae.

Water

Water is the most important input in the hatchery. Pristine, high-salinity (32–35 ppt) water is required. Since water is one of the most important sources of disease, it is treated very carefully before either broodstock or larval prawns are introduced.

Incoming water is filtered intensively and usually passed through UV light to minimise the intake of unwanted bacteria and other pathogens. The water is treated with EDTA to chelate heavy metals, and may be chlorinated in the tanks before living animals are introduced. Chlorine has to be allowed to dissipate before the tanks are seeded; this is done with sunlight and vigorous bubbling with air stones. Sodium thiosulfate may be used to neutralise the chlorine in the tank.

Feed

Feed for broodstock is usually fresh or frozen, and consists of squid, liver, mussels, polychaete worms and artificial high-protein pellets. It is supplied by local bait feed suppliers. Pelleted feed is supplied by an importer or distributor.

Larval feed consists of imported microencapsulated feed, supplemented with algae of many species—for example, Chaetoceros calcitrans, C. muelleri, Tetraselmis spp. and Skeletonema costatum. Algal starter cultures are usually purchased from CSIRO and grown up on-site. Another live feed used is imported brine shrimp (Artemia spp.), which come in cyst form in tins, and are rehydrated and hatched on-site.

Personnel

Most hatcheries are operated by their owners. Some are solely a family operation, but most employ two or three qualified technicians with hatchery experience.

Equipment

Equipment is fairly specialised and consists of fibreglass tanks of various sizes, from 1 t to 25 t or more. Some hatcheries use concrete tanks.

Air blowers, usually Roots blowers, are used to maintain a constant supply of air to the tanks. Most hatcheries have a stand-by generator in case of public power failure. Some hatcheries have well-equipped laboratories for water quality analysis and disease monitoring, whereas others have very little support equipment.

Stores

An adequate supply of feed is necessary to complete a hatchery run. Chemicals used for cleaning and disinfecting tanks, air lines and air stones are also kept on-site. Filter material, screens, dip-nets, weighing scales, freezers for feed storage, maintenance tools and spare parts are all kept in an adjacent storeroom.

Vehicles

Workers live off-site and drive private vehicles to work. Usually, a hatchery that is associated with a farm, or comes under the same ownership, will have 4WD or utility vehicles. Most hatcheries have transporter tanks that are hitched to trucks to make routine larval animal deliveries to farmers on completion of sales. When the hatchery has ponds on the property, four-wheeled all-terrain vehicles are commonly used.

B3.4.4 System outputs

Animals

Post-larvae are the only product. They are harvested from the grow-out tanks by concentrating them in small containers of a given volume so that a volumetric count can be made. They are then poured into a transporter and taken to the farm, or packed into plastic bags containing salt water and packed into foam boxes for shipping to farms via air transport. Excess feed, including algae, may be flushed out at the end of a production cycle.

Water

During the culture period, water is usually not discharged. Generally, hatcheries are required to have a settlement or holding pond for water outflow, as part of the conditions of their aquaculture permit. Treatments such as chlorination can be undertaken in these holding ponds. Tank discharge at harvest is high in organic matter through accumulation of faeces, uneaten feed, and some dead larval animals and moult material.

Waste

Dead post-larvae are washed out with wastewaters into holding or settlement ponds. Spent broodstock is generally cooked and eaten.

Equipment

Movement of disease from one tank to another in the hatchery situation is a real risk. All equipment is thoroughly cleaned and disinfected between hatchery runs. Regular dry out of all tanks, pipes and holding ponds is advisable between runs. Each tank has its own individual accessories. Cross-contamination should be avoided because any importation of disease (viral, bacterial or another infectious cause) can trigger a mass mortality event.

B3.4.5 Groups involved

Groups involved in production of post-larval prawns include:

• 
  the NSW Prawn Farmers Association
  
• 
  the Australian Prawn Farmers Association
  
• 
  the Mackay Mariculture Association
  
• 
  the Mackay Prawn Farmers Association
  
• 
  the Queensland Aquaculture Industries Federation
  
• 
  the National Aquaculture Council
  
• 
  state departments of agriculture and fisheries
  
• 
  water authorities
  
• 
  environmental protection agencies, and other environmental groups and agencies.
  

B3.4.6 Legislation and codes of practice

The Australian Prawn Farmers Association has published an Environmental code of practice for Australian prawn farmers (www.nretas.nt.gov.au/__data/assets/pdf_file/0020/20369/appendix3.pdf). Each hatchery normally establishes its own protocols and manual of standard operating procedures, which include hatching techniques, sanitation, grow-out and standard methodology. Several farms have also embraced environmental management systems implemented through ISO 14001 standards.

Relevant legislation is listed in Appendix 1.

B3.4.7 Occupational health

Chemicals (e.g. disinfectants, antifungals, antibiotics) that may pose a health risk are commonly used in hatchery operations.

Information about seafood-borne disease in humans can be found in Appendix 2.