A view on cage culture
Cage based aquaculture in the inland open waters of India
by Dr B Laxmappa, Department of Fisheries, India,
Globally, India stands second in inland fish production next to China, but there is a huge gap in fish production between these two leading aquaculture countries. The prime objective of cage culture in inland open water is the stocking of reservoirs and culture of economically important fishes for augmenting fish production.
Cage culture in inland open waters is being evaluated as an opportunity to use existing reservoirs and meet the increasing demand for animal protein in the country. Reservoirs in India offer substantial scope for implementation of technology for intensive cage farming to realise water productivity, entrepreneurship and employment opportunities.
Cage culture is an emerging technology through which fishes are reared from fry to fingerling, and then from fingerling to marketable size while kept captive in an enclosed space that maintains the free exchange of water with the surrounding water body. A cage is enclosed on all sides with mesh netting made from synthetic material that resists decomposition in water for a long period of time.
In India, cage culture in inland water bodies was initiated for the first time in air breathing fishes in swamps, for raising major carps in running waters in Jamuna and Ganga at Allahabad, and for raising carps, snakeheads, and tilapia in lentic (still water) bodies of Karnataka.
Thereafter the cages have been used for rearing fry in many reservoirs and floodplain wetlands to produce advanced fingerlings for stocking main water bodies. India has 19,370 reservoirs spread over 15 states with an estimated 3.15 million ha surface area at full capacity, and this is expected to increase due to the execution of various water projects in the country.
Evolution of cage culture
In India, the Central Inland Fisheries Research Institute (CIFRI) attempted cage culture in the 1970s with the production of air-breathing fish in cages. Subsequently, trials with major carps were conducted in cages installed in river Yamuna and Ganga at Allahabad. Similar attempts were made with common carp, silver carp, rohu, snakeheads and tilapia in a still water body of Karnataka. The growth of cage farming got momentum during 2010-2012 with funding support from National Fisheries Development Board (NFDB), National Mission on Protein Supplementation (NMPS), Rashtriya Krishi Vikas Yojna (RKVY), etc. This paved a way for the dissemination and adoption of this technology in a number of reservoirs belonging to more than 15 states in "Mission Mode" through NMPS scheme. The states of Jharkhand, Chhattisgarh, Madhya Pradesh, Maharashtra, Telangana and Andhra Pradesh have widely adopted and upscaled cage culture technology.
Cage culture has received substantial attention from researchers, entrepreneurs and policy makers in recent years. At present, there are more than 15,000 ﬂoating cages of different dimensions and materials, such as bamboo, galvanized iron (GI), high-density polyethylene (HDPE) in inland open water resources of India.
In India, GI cages and HDPE modular cages are being widely adopted for ﬁsh farming in inland waters. Modular "Pontoon type" ﬁbre or HDPE cages have gained popularity due to their robustness, long life and low maintenance cost. The new generation cages of size 5 x 5 x 4 m or 6 x 4 x 4 m are commonly used in reservoirs. The private ﬁrms and entrepreneurs are now venturing into cage culture due to high proﬁtability.
Species and stocking rate
The stocking density of fish depends on the carrying capacity of the cages and feeding habits of the cultured species. For those species which are low in the food chain, stocking will also depend on the primary and secondary productivity of the sites.
The optimal stocking density varies with species and size of fish and ensures optimum yield and low disease prevalence. The culture of a number of candidates fish species like striped catfish (Pangasianodon hypophthalmus), Tilapia (Monosex), puntius (Puntius javanicus), Labeo bata, barramundi (Lates calcarifer), giant freshwater prawn (Macrobrachium rosenbergii), besides air breathing ﬁshes, snakeheads and ornamental ﬁshes have been attempted in cages and encouraging results obtained in terms of growth and survival.
Many biological, climatic, environmental and economic factors affect the feeding of fish in cages. Fish growth rate is affected by feeding intensity and feeding time. Each species varies in maximum food intake, feeding frequency, digestibility and conversion efficiency. These, in turn, affect the net yield, survival rates, size of fish, and overall production from the cage. The artiﬁcial ﬂoating feeds with crude protein varying from 20 percent to 30 percent are being used for iridescent shark (P. hypophthalmus) farming in cages. The feed conversion ratio (FCR) of 1.3-1.5 has been obtained for table size fish production of Pangas species.
Regular monitoring of some water quality parameters, including dissolved oxygen, pH and free ammonia, inside cages is necessary. Normally in Indian reservoirs, with the objective of raising fingerlings in cage culture, water quality is not conducive to good fish health and on very rare occasions, with a dense algal bloom, some parameters cause stress for the fish. Therefore, cages should be cleaned with a soft coir brush fortnightly to remove biofouling organisms like algae, sponges and debris. Routine checking for loose twine, torn meshes from predators, anchors and sinkers is also necessary.
Harvesting and production
Cages are usually harvested by moving them into shallow water, crowding the fish into a restricted area, and then simply dipping the fish out of the cage. Or, the cage can be lifted partially out of the water so that the fish are crowded into a smaller volume, and then the fish dipped out. This makes it possible to partially harvest fish from cages as needed for local niche markets or personal consumption. The CIFRI has facilitated implementation of cage culture through introduction of non-native species and has achieved a production level of 50 kg per m3 in cages stocked at 60 per m3. Although there is enormous potential for fish production in cages, a modest beginning of 15,000 cages in Indian reservoirs could produce 67,500 tons of fish.
The oligotrophic nature of medium and large reservoirs of the country offer ample scope for implementation of cage culture technology for intensive ﬁsh production system. The cage culture of commercially important diversiﬁed species will be useful for realisation of water productivity, entrepreneurship and employment generation paving a way for the empowerment of ﬁshing folk in the country. Stocking with the right fish species, using seed of appropriate size and introducing it at the right time are essential to optimising fish yield from reservoirs.