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Guidelines for Sea Cage Farming in India

Mariculture – the farming of marine organisms for food - is the fastest growing sub-sector of aquaculture. Enhancing fish production from inland sector has limited scope and the major portion of the additional demand has to come from mariculture.

Sea cage farming is viewed as a major option for increasing the seafood production and has been expanding rapidly in recent years at global level. he ICAR-Central Marine Fisheries Research Institute (CMFRI) has projected that even if 1% of the inshore waters is used for cage farming, we can deploy 8,20,000 cages with a production potential of 3.2 million tonnes.

The National Fisheries Development Board (NFDB) has released the Guidelines for Sea Cage Farming in India with the objective to augment fish production in a sustainable manner through sea cage farming to meet the increasing demand for seafood.

Sea Cage Culture

Sea cage culture involves growing fishes in the sea while being enclosed in a net cage which allows free flow of water. It is a production system comprising of a floating frame of varying dimensions and shape, net materials and mooring system, to hold and culture a large number of fishes.

Advantages of Sea Cage Farming

  • Cage farming can be undertaken in open seas, sheltered bays or lagoons having suitable water quality and with prior permission from concerned government authorities. Thus, the vast unutilized areas in the sea can be brought under mariculture practices.
  • Production per unit (m3) in cage culture is 50 times more than shore based systems.
  • Recurring expenditure associated with development and maintenance of infrastructure are lower in cage farming compared to shore based farming practices.
  • Stock monitoring is simple in cage farming, facilitating regular observation of behavior, feeding and growth that are critical in avoiding problems related to stress and disease outbreak.
  • Harvesting is easy and can be planned as per the demand, offering better quality product at higher price.

Site Selection

Choosing a site in cage farming is crucial because it impacts the economic viability of farming. Site selected should provide optimum water quality to avoid stress conditions and achieve maximum growth of farmed fish, and ensure proper and secure installation of cages, logistic and other support for supply of inputs, harvesting and marketing of fish. Sea cage site has a direct bearing on operational cost, fish mortality, production and overall profitability of farming operation.

Exclusion of areas for cage farming : Sites which are active fishing zones and close to harbours/ fish landing centres and navigation channels, defense areas, marine protected areas, coral reefs, mangroves, areas under coastal management plan, points of industrial effluent discharge, sewage pollution, heavy freshwater discharge by rivers, presence of underwater pipelines, telecom cables, explosives dumping and areas of historic ship wreck are to be avoided during site selection.

Environmental Parameters

  1. Physical Factors
    • Depth : Culture site should have a minimum depth of 6 m at the lowest low tide. A clearance of minimum 2 m should be available between the cage net bottom and seabed. This will maximize water exchange, reduce oxygen depletion and encourage flushing-out of metabolic and feed wastes that accumulate under the cage. Depth of farming site determines mooring design and length of mooring chains, affects routine net and mooring line inspection, etc.
    • Current : Seawater current speed of 0.5 – 1.0 m per sec is considered ideal. Current speed above this will exert very large force on cages and mooring systems and cause mortality of farmed fishes. Current speed influences water exchange, feed dispersion, net shape and volume, solid waste dispersal and effective monitoring.
    • Shelter : Sheltered area is preferred as it will protect cages in extreme weather conditions. However, in such areas after long-term farming operations, when food waste and fecal matter will settle, there is a tendency for large quantities of waste to accumulate and pollute the seabed at the cage site. Thus, for undertaking long-term farming operations, semi-exposed and exposed areas are preferable.
    • Wind and Waves : Wind affects the wave height and when waves are high it will affect the accessibility to cages and it becomes difficult to do routine activities like feeding fish, monitoring cages, etc.
    • Seabed : The nature of seabed determines the mooring system and type of anchors to be used. Thick mud, clay, sand and pebbles will provide good holding for anchors. Seabed having rocks, stones, corals will require a deadweight (gravity) anchorage with Gabions (mesh boxes filled with rocks or concrete blocks.
    • Water Quality Criteria : Cage site should have good water quality to meet the biological requirement of the farmed species. These criteria include optimum temperature, salinity, pH and dissolved oxygen. The water should be free from excessive suspended solids, frequent algal blooms and disease causing organisms.
  2. Logistics : Distance from shore to cage site should be at the minimum to reduce operational expenses. Road connectivity for transporting cage materials, feed, harvested fish, etc., is required for a successful operation of sea cage farm. The CMFRI and State Fisheries Departments should take initiative to identify suitable sites for sea cage farming and map them in GIS platform to facilitate proper planning and effective implementation. This will benefit the entrepreneurs to select ideal locations to start sea cage farming ventures.
  3. Integrated Systems : To promote and expand sea cage farming in India, an integrated approach is vital. In this context creating facilities for manufacture of cage frames, fabrication of cage nets, mooring assembly, establishment of hatcheries, nursery rearing units, feed mills, post-harvest processing units, etc., are to be considered as part of the cage farming system.

Materials and Design of Sea Cage

A sea cage essentially comprises of cage frame and net cages. For sea cage fabrication the materials used should be sturdy enough to withstand rough sea conditions and weather. Cage frames are fabricated either with High Density Poly Ethylene (HDPE) or Galvanized Iron (GI) material to withstand rough conditions in the Indian seas. HDPE pipe PE100 or GI pipe (1.5”) B/C Class are preferred for cage frames. When GI pipe is used, all joints are double welded and the GI cage frame is epoxy coated and floated on air-filled HDPE barrels (200 litre, 8-10 nos.). Sea cages are preferably circular-shaped as they can withstand sea conditions better than rectangular or square shapes.

Specifications for 6 m Diameter HDPE Cage

The sea cage frame has two collar rings designed with flotation properties and a middle ring as catwalk in between them (Fig. 1). In case of HDPE the pipe-ends are joined by using a fusion welding process for plastics. The two collar rings for flotation are filled with polyurethane foam (PUF) or thermocol. The two collar rings, the middle catwalk ring and the handrail ring are all held in place by means of various support pipes, brackets and T-joints. The pipe used for handrail is without PUF inside and the brackets made of galvanized steel are corrosion-free and are fitted to the diameter of the pipes. The maximum height of handrail should be approximately 100 cm (shorter than the shortest person). The service systems (catwalk, handrail. etc.) are required for operation and maintenance activities like feeding, cleaning, monitoring, grading, etc. The minimum width for catwalk is approximately 60 cm. The brackets/ base supports, vertical and diagonal supports hold together the collar rings, catwalk ring and the handrail. They also give additional stability and sturdiness to the frame structure.

The ballast pipe is another support system required to maintain the shape and structure of the net bags (Fig. 2). Normally 1.5 inch (38 mm) diameter HDPE ballast pipe with holes at regular intervals, for the free flow of water, is used. Metal lines are inserted inside the pipe for increasing weight so that the ballast remains submerged in water.

structure of cages

Technical Specifications

  1. Base Collar
    • Inner Ring – 6 m diameter circle (HDPE, 140 mm diameter pipe)
    • Outer Ring – 7 m diameter circle (HDPE, 140 mm diameter pipe)
    • Middle Ring (Catwalk) – 6.5 m diameter circle (HDPE, 90 mm diameter pipe)
    • Base Supports – 8 Nos. (HDPE, 250 mm diameter pipe)
    • Vertical Supports – 8 Nos. of 0.8 m length (HDPE, 90 mm diameter pipe) to connect the base supports to the circular top handrail of same diameter with 8 Nos. of suitable T-joints. The T-joints should be fixed with fusion welding as well as with SS bolts and nuts. 16 hooks (2 inch SS) must be fixed to hand railing to tie the bird net.
    • Diagonal Supports – 8 Nos. (HDPE, 90 mm diameter pipe), to connect the catwalk ring to the circular top handrail with T-joints fixed with fusion welding as well as with SS bolts and nuts.
    • Base, Vertical and Diagonal Supports can be replaced with any suitable brackets (metal/ HDPE/ equivalent).
    • All pipes should be made of HDPE, filled with PUF (polystyrene or equivalent), 10 kg pressure, PE-100, PN-10, and ISI Standard is 4984
  2. Handrail
    • 6 m diameter circle (HDPE, 90 mm diameter pipe), fitted about 1 m above the Inner Collar Ring and connected by vertical as well as diagonal supports with the Base Collar Rings (Fig. 1 and 2).
  3. Mooring System
  4. Mooring system/assembly holds the cage in desired position and at desired depth using mooring lines, chains and anchors. Individual cages can be moored using single-point mooring system (Fig. 3) and a battery of cages can also be moored by means of grid-mooring system.
    Single-point Mooring System components required for 10 cages:
    • Anchors (embedment type) / Gabion Boxes – 100 kg each, 10 nos.
    • D-Shackles – for 12.5 tonne SWL (Safe Working Load), 3 x 10 = 30 nos.
    • Mooring Chains – 38-42 mm thick, length four times the depth at site, 10 nos.
    • Buoys – 200 litre buoyancy, 4 x 10 = 40 nos.
    • Anchor Marker Line – poly-steel rope of 36 mm diameter and 37 m length
    • Mooring Rope – poly-steel rope of 48 mm diameter, 3-4 strands, and 100 m length. Also splicing, steel thimble and oval ring of 22 mm at one end, 10 nos.

mooring system for Sea Cage

Net Cages

Mesh size for the net cages must be selected according to the species of fish farmed and also to ensure good water exchange. Proper water flow enhances water quality, reduces stress, improves feed conversion and allows holding more fishes. Net cages should be as per the dimensions of the cage frame and depth of water at the site. They must be securely fastened to the cage frame. For sea cage farming, 3 types of nets are essential:

  1. Outer Predator : Net Because of the turbulent nature of the sea and presence of carnivorous animals, suitable outer net cage is essential to prevent entry of predators in sea cage culture. Considering the strength, durability and cost factor, usually braided UV treated HDPE netting of 3 mm thickness and 80 mm mesh size is found very effective and recommended. Dimensions of predator net cage – 7 m diameter and 5 m depth (entirely submerged) (Fig. 2).
  2. Inner Fish Rearing Net : For fabrication of inner fish rearing/grow-out net cage, twisted HDPE netting of 0.75-1.5 mm thickness and 16 - 40 mm mesh size is selected depending on the size of cultivable species. Dimensions of fish rearing net cage – 6 m diameter and 5 m depth (4.0 m submerged and 1.0 m up to the handrail; volume 113 cubic metres) (Fig. 2).
  3. Bird Net : To prevent predatory birds from preying on fish, a protective bird net must be overlaid on the cage frame. HDPE twisted and UV treated 1.25 mm twine and 60 - 80 mm mesh size will be ideal for a bird net.

High Density Polyethylene knotted netting is preferred for net cages. The mesh size of the net cages depends on the size of individual farmed fish. Three sets of net cages of three different mesh sizes are required during the farming operation (18 mm, 25 mm and 40 mm). To maintain the cylindrical shape of the net cages, ballasts of appropriate weight should be used. Concrete blocks tied at suitable intervals can be used. Alternately, HDPE pipe of 1.5 inch (38 mm) diameter inserted with MS chain or wire rope of 10 mm thickness can be employed.

Net Specifications

  • Predator Protection/ Outer Net Cage – HDPE braided 3 mm; 60 mm/ 80 mm mesh.
  • Fish Rearing/ Grow-out/ Inner Net Cage – HDPE twisted; 18 mm/25 mm/40 mm/60 mm mesh.
  • Bird Net – HDPE twisted/ Nylon; 60-100 mm mesh.
  • Predator net cage is uniform for all species, made of braided HDPE (3 mm twine) and usually 80 mm mesh; Bird net is also uniform, made of twisted HDPE or Nylon (1 mm twine) and up to 100 mm mesh.

Species Selection

Cage culture in the sea requires a fish variety that meets criteria such as suitability for marketing, commercial importance, consumer acceptance, easy to culture, adaptability to the cage environment, acceptance of formulated feeds, faster growth rate and resistant to common diseases.

As per the above criteria, Cobia (Rachycentron canadum), Silver Pompano (Trachinotus blochii), Seabass (Lates calcarifer), Snappers (Lutjanus sp.), Groupers (Epinephelus sp.) and Spiny Lobster (Panulirus sp.) are highly suitable for sea cage farming.

Seed

Quality of fish seed is of vital importance for the success of grow-out culture in cages. Uniform size seeds appropriate for the mesh size of the fish net cage should be stocked to prevent their escape. This will also help in selecting the correct sized feed for fishes, avoid wastage of feed and reduce cannibalism. Seeds should be healthy, free from diseases and deformities.

The most vital issue for the expansion of the sea cage farming in India is the shortage of fish seeds. Presently seed of Cobia, Pompano, Seabass and Groupers are being produced in a few hatcheries in the country. Apart from these species, seeds of fishes like Mullets, Snappers, Milkfish, etc. collected from the wild can also be used for cage farming. To meet the growing demand from farmers, there is an urgent need to produce sufficient quantity of seed either through commercial hatchery production or by importing till we achieve self-sufficiency in seed production.

List of Marine Fish Hatcheries

  • CMFRI, Mandapam, Tamil Nadu  - Cobia, Pompano
  • CMFRI, Visakhapatnam, Andhra Pradesh - Grouper, Pompano
  • RGCA (MPEDA), Pozhiyoor, Kerala - Seabass, Cobia, Pompano
  • CIBA, Chennai, Tamil Nadu - Seabass

Stocking

Stocking appropriate size and number of fish seed in cages is very crucial for the success of cage farming. After allowing the hatchery produced spawn to grow for a period ranging from 30 to 60 days, fish seed can be stocked in cages. Nursery rearing of seed is essential for all species and it can be done as a separate activity, in land based nursery ponds or hapas held in ponds or in floating nursery cages, by individuals or groups at different localities to support sea cage farming with ready to stock fingerlings. Healthy, uniform-sized fingerlings should be procured for stocking in cages. The fingerling stocking details are given below:

Species Stocking Size (Length/ Weight)Stocking Density (Nos./ m 3 )
Cobia 15 cm/ 35 g 8-10
Pompano 10 cm/ 35 g 30-40
Seabass 10 cm/ 30 g 30-40
Grouper 15 cm/ 40 g 15-20

Feeds

Any material used for feeding contains the following five principle constituents: (i) Protein, (ii) Carbohydrate, (iii) Fat, (iv) Minerals and (v) Vitamins. Proteins are essential for growth of the animal and a deficiency can lead to growth retardation. The nutrient requirements of marine carnivorous fishes (as %) are given below:

Size of Fish MoistureCrude ProteinCrude FatCrude Fibre
Fry-Fingerling (1 - 20 g) <12 >42 >5 <4
Juvenile (20 - 50 g) <12 >40 >5 <4
Grower (50 - 300 g) <12 >38 >5 <4
Marketable Size (>300 g) <12 >35 >5 <4

Marine fishes require higher protein (35-40%) feed for their optimal growth. Based on growth of the fish, size of the feed pellet should be adjusted. Normal feeding rate is 10% of the body weight for juvenile fishes which can be reduced to 3% body weight as farming progresses. A feed with an FCR of 1:2 is advisable. Only recommended ration should be given to fishes since overfeeding leads to wastage and environment pollution.

Feed Ingredients

Ingredients used for making feeds can be classified as protein rich ingredients which are mainly fish and meat products of animal origin and oilcakes of plant origin. Energy rich ingredients are mainly cereals and cereal byproducts. Other than these there are non-conventional feed resources (NCFR) which are used in feed manufacture. Apart from these ingredients, mineral mixtures, vitamin mixtures and other additives such as oil, phospholipids, carotenoids are also added according to the needs. Non-nutrient additives such as synthetic binders, anti-oxidants and anti- fungals are also added.

Feed Formulation

With a fair knowledge of nutrients and the feed ingredients, the next aspect to be understood is the need for blending of the ingredients to have a nutritionally complete and balanced feed mix. A nutritionally complete feed can be made by mixing ingredients on a scientific basis which will be effective in producing the desired results in terms of fish production. The feeds should have the physical properties suitable for the fish to consume it with minimum loss of nutrients in water. Feed technology evolved from a dry mash to a wet ball and to a pellet. Now, pellets are produced such that they sink, slow-sink or float depending upon the feeding habit of fish. For cage farming floating or slow sinking pellets are found to be appropriate. Production of floating and slow-sinking pellets is done using extruders, which are available in India or can be imported.

Feed Storage

During storage, feeds undergo deteriorative changes which not only lower their nutritive value but also affect their palatability and appearance. Feeds should be stored in dry ventilated warehouses away from direct sunlight at more or less constant temperature. All feeds should be used within the prescribed time (preferably within two months of manufacture) and inspected regularly. During long storage there may be changes such as fungal growth, degradation of vitamin potency and fat rancidity. Unnecessary handling may damage feed bags and reduce pellets to powder that is usually not consumed by fish and wasted. Pests like rats, cockroaches, etc., must be strictly controlled in the storage, to avoid contamination. Proper storage of feed is simple, but it is important to keep its quality high.

Feeding Schedule

Feeding rates, frequency of feeding and time of feeding are important factors to be considered in cage farming. Feeding rates and frequencies are related to age and size of the fish. Fish larvae and fry need to be fed on a high protein diet more frequently. When fishes grow bigger, feeding rates and frequencies can be reduced. Feeding fish is a labour-intensive activity and the frequency has to be adjusted in such a way that it is economically viable. Generally, growth and feed conversion increase with increase in feeding frequency. Feed consumption is also influenced by time of day, season, water temperature, dissolved oxygen levels and other water quality parameters. Even though several feeding charts are available, it is better to construct one of your own with information on: Days of Culture (DOC), Fish Weight, Protein in Feed, Meal/Day, Feed Consumed as % of body weight, Average Daily Gain (ADG) and Feed Conversion Ratio (FCR). Indicative feeding charts for Cobia, Silver Pompano and Seabass are as follows:

Feed chart

Growth Rate

Salinity above 25 ppt is essential for optimal growth of Cobia; whereas Silver Pompano tolerates even salinity of 10 ppt. Farming duration usually ranges from 7 to 8 months for Cobia and Silver Pompano while it is 6-8 months for Seabass, to attain optimum marketable size.

Cage Maintenance

Cage Farm management involves optimizing production at minimum cost. Efficient management largely depends on the competence and efficiency of farm operator with regards to feeding rate, stocking density, minimizing loss due to diseases and predators, monitoring environmental parameters and maintaining efficiency in all other technical aspects. The entire structure including cage frame and mooring must be routinely inspected and necessary maintenance and repairs should be carried out. Bio-fouling clogs the mesh of net cages and thereby reduces rate of water exchange causing stress due to low oxygen and accumulated wastes leading to mortality of fish. The rate of fouling depends not only on the mesh size of the net cage, but also on temperature and productivity of the water at the cage site. Therefore, timely exchange of fish rearing net cage is to be done, by replacing with a fresh net cage, to ensure good water quality and facilitate faster growth. Also, as fish grow bigger, net cages of appropriate mesh size are to be used.

Health Management

Disease outbreaks can occur as a result of intensive farming in cages. Infectious diseases are mainly due to waste accumulation, crowding, handling, variations in water quality parameters and bio-fouling. The most common disease that occurs in cages is Vibriosis caused by Vibrio a bacterial species. Cage abrasion can cause fin and skin damage to farmed fish. Occurrence of infections/ diseases can be minimized by selecting good site, optimal stocking density and careful handling of fish stock. Fish farmers should maintain a record of weather, water quality parameters, feeding rate, length and weight of fish sampled, fish behavioral changes, net cage exchange details, etc. These records provide useful information for analysis of health status.

Good Management Practices

Good management practices (GMPs) need to be adopted to satisfy consumer demand and expand the market by offering quality farmed products that meet food safety standards. Adoption of GMPs also helps fish farmers to achieve higher economic returns. Some of the key factors in GMP include:

  • Avoiding over-stocking of fish fingerlings.
  • Monitoring growth rate at appropriate time intervals.
  • Feeding fishes with pellets of good quality and right quantity.
  • Regular cleaning and exchange of net cages for effective water exchange.
  • Avoiding use of antifouling paints/ chemicals.
  • Timely removal and proper disposal of dead fishes.
  • Periodic monitoring of water temperature, dissolved oxygen, pH, etc.
  • Close observation of fish behaviour while feeding them, to assess health status.
  • Integrated Multi-Trophic Aquaculture (IMTA)/ Polyculture of compatible species in cage

Environmental Impact

Cage culture system releases waste to the aquatic environment in the form of uneaten feed, feces and other debris. These may accumulate beneath the cages leading to reduction in dissolved oxygen. The tendency of large quantity of waste to settle on the sea bed is greater at sheltered inshore sites. Continuous farming for several years at the same site in sheltered areas is to be avoided. Change of site after a number of crops should be done. Otherwise, semi-exposed/ exposed sites having good tidal flushing are selected to prevent accumulation of wastes at the bottom of the cage. Adequate spacing between cages and farms is also an essential management practice to reduce the spread of diseases. Indiscriminate use of antibiotics and their release into aquatic environment may result in development of antibiotic resistant bacteria. Cage culture can also introduce diseases, transmit parasites and cause changes in aquatic flora and fauna. Hence, carrying capacity of the environment, as per the nature of the site, has to be given prime importance while undertaking sea cage farming.

Harvesting Protocols

Harvesting can be done as per the market demand to ensure maximum returns. Partial harvesting of stock may be practiced, by harvesting the larger fish first, to avoid glut in the market and consequent fall in sale price. Records of harvest should be maintained at the site. It is necessary to have a post-harvest and marketing strategy while undertaking large scale sea cage farming activity.

The production centres should have facilities such as proper craft and gear to harvest fish, facilities for icing, holding and storage of fish, live-fish transport, linkages to post-harvest processing centres and market chains.

Safety Measures

Cage culture in the sea involves working in a risky environment. Hence adequate safety measures should be taken to prevent accidents including loss of life. Life-saving equipment like life-buoys/ jackets, communication devices, and first aid boxes at the cage site should be made mandatory. All persons while working at the sea cage should wear life-jackets.

To avoid poaching or vandalism effective watch and ward arrangement should be made at the sea cage site. Also, to alert fishing craft and seafarers and to indicate the location of sea cages and their moorings, Maritime Signal Flags and Solar Beacon Lights may be positioned on the cages.

To access the complete guidelines including Economics of Sea Cage Farming, Financial Assistance, List of Cage Manufacturers, List of Feed Manufacturers, etc. click here.

Source : National Fisheries Development Board



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