Trout Culture in Recirculatory Aquaculture System (RAS)

Introduction

To utilize the cold water resource, number of fast growing and economically viable species has been introduced, which include species of Carp and Trout. The Rainbow Trout (Oncorynchusmykiss) is a temperate region (cold water) carnivorous fish species which needs crystal clear and highly oxygenated water, thus well suited for water systems of Himalayan states. Europe, North America, Chile, Japan and Australia are the main producer countries. Rainbow Trout farming has great potential in India since Trout is one of the high value species and having high demand in both domestic and international market. Trout farming is common in the states of Jammu and Kashmir, Himachal Pradesh, Uttarakhand, Sikkim, Arunachal Pradesh and Ladakh due to the suitable temperature range (5° to 18°C). These states have established a well-developed infrastructure for Trout production depending on the availability of water in required quantity and quality, i.e. from springs and snow/glacierfed streams. Trout farming in India is having huge potential. These states have an ample cold water resources and is suitable for the culture of high value cold water fish like Trout. 

Trout culture in raceways has been traditionally practised for hatchery production of fish, where a flow-through system is maintained to provide the required level of water quality. Environmental and water quantity parameters are easier to manage in raceways than in pond systems. Flowing water flushes wastes from the culture units and also forces the fishes to exercise thus help in the better survival of the fish. The shallow water in raceways allows visual observation of the fish so that diet and /or disease problems can be promptly corrected. Feeding and harvesting are generally easier in raceway systems. Feeding and disease treatment are easily managed in raceway systems than in open systems or ponds. However, Rainbow Trout are farmed extensively overseas both in Recirculatory Aquaculture System (RAS) as this land based aquaculture practice enables farmer to use water judiciously. Farming trout in RAS could overcome many of the issues faced by Trout farmers. In RAS, chances of disease outbreak can be minimised, judicial usage of water and land area helps farmer to get more profit. Also, exposure of stock to stress can be reduced for some factors such as adverse weather, unfavourable temperature conditions, pollution incidents and predation.

Advantage of Recirculatory Aquaculture System (RAS)

• Longer average life of tanks and equipment
• Reduced dependency on antibiotics and therapeutants hence, advantage of getting high quality ‘safe’fish
• Reduction of direct operational costs associated with feed, predator control and parasites.
• Potentially eliminate release of parasites to recipient waters
• Risk reduction due to climatic factors, disease and parasite impacts
• RAS production can promote versatility in terms of location for farming, proximity to market
• Enable production of a broad range of species irrespective of temperature requirements.
• Feed management is potentially greatly enhanced in RAS when feeding can be closely monitored over 24h periods
• Exposure of stock to stress on RAS farms can be reduced for some factors such as adverse weather, unfavourable temperature conditions, pollution incidents and predation
• Enable secure production of non-endemic species
• Judicial use of water and land areas 

Facts about Rainbow Trout

• Hardy in nature, easy to spawn and fast growing
• Large fry can be easily weaned on to an artificial diet (usually zooplankton)
• Maturity in 3-4 years
• Temperature tolerance range 0 °C to 27°C,
• Optimum water temperature range is 5°C to 18°C
• Monoculture is the most common practice in trout culture, and intensive systems are considered necessary in most situations to make the operation economically attractive.
• Preferable water source is Spring or snow fed stream, which is crystal clear and silt free having pH range of 7 to 8.
• Preferable water flow rate is 15 litre/min for fry and 0.5 litre/kg/min for fish below 250 gm. 

Production Cycle of Rainbow Trout

Pre-stock management

• The seed rearing tanks should be cleaned before the fry/fingerlings arrived. Once the preparation of the tanks is over, water supply should be checked
• Trout is sensitive to changes in water temperature, especially when it is from cold to warm. The smaller the fish, the more sensitive they are, and susceptible to thermal shock particularly to warm thermal shock. Therefore, it is important to raise or lower the temperature of the transport water slowly in steps of 0.5 °C/min in order to ensure safety
• The optimal velocity of water in the raceway is 2–3 cm/sec (1.2–1.8 m/min) for smaller fish and 4–10 cm/sec (2.4–6 m/min.) for larger ones

Post-stock management

The physico-chemical parameters and hygiene leads to successful culture of Trout fish:

• Optimum temperature: 5 degree C to 18 degree C
• Dissolved oxygen: 5.8 to 9.5 mg/l
• pH: A neutral or slightly alkaline pH is best for the trout. Optimum pH level of 7-8 is ideal for the growth
• Turbidity: Clear water without any contamination is required for culture. However, the turbidity should not be more than 25 cm in the Secchi disc
• Hygiene: The cleanliness is a very important factor in Trout farming. The fish should be cleaned and disinfected either with 10% formalin or 4 ppm KMnO4 solution periodically through Dip treatment. The infected fish should be immediately removed from the tank and due care should be taken to consult some fishery expert regarding the disease, if any

Seed stocking

Fish seed must be transported in water with optimum temperature. It is also important to release fish seed after proper acclimatization. Therefore, the bucket or basin in which fish are transferred should be submerged into the water where the fish are released for proper acclimatisation.

Feed

Commercial Trout feed manufactured at Govt./Pvt. is available. Feeding @ 4-6 % of body weight is necessary for the fingerlings for better growth but due consideration should be given to the water temperature for following the feeding schedule. At the water temperature range of 10-12C, feeding schedule of 6% is optimum but when it increases to 15C, the feeding schedule to be lowered to 4%. The optimum growth rate per month is 30-40 g.

Re-circulatory Aquaculture System(RAS) Components for Trout Culture

• Insulated shed/ Building
• Store cum office for feed and accessories
• Pump house
• Grow out tanks: Circular cement tanks/ FRP tanks, including inlet, outlet central drainage
• Settling tanks for sludge
• Water Storage (sump) tanks
• Overhead tanks
• Mechanical (Hydraulic) filters, Glass wool/ muslin cloth filter mat
• Pumps and motors
• Power generator
• Sludge collector, settable/ dissolved solid collectors
• Bio-filters, UV units
• Electrification
• Automatic feeder (wherever required)
• Aeration system (air/ oxygen), Carbon dioxide trapper system (degasser)
• Water testing kit
• Water supply system, bore well etc (wherever required)
• Inputs such as Seed, Feed, additives and supplements, electricity/ Diesel, man power etc.

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Source : National Fisheries Development Board