Cage Aquaculture


Cage aquaculture, though relatively new to the inland aquaculture scenario of the country, brings in new opportunities for optimizing fish production from the reservoirs and lakes, and also developing new skills among fishers and entrepreneurs to enhance their earnings. However, unplanned expansion of any activity can lead to adverse impacts in terms of environmental integrity and social equity.

Cage is an enclosed space to rear organisms in water that maintains free exchange of water with the surrounding water body. ‘Pens’ are essentially portions of a water body cordoned off by erecting a fence like structure. Usually pens are enclosed portions of the lake margin, with fencing on three sides; the free fourth side being contiguous with the land. But, pen can also be away from the shore with fencing on all the four sides. The main difference between a pen and a cage is: pen bottom is never covered so that the soil water interface of the water body is not compromised. Enclosure aquaculture in the context of inland fisheries in India refers to both ‘cage culture’ and ‘pen culture’.

Traditionally, Freshwater fish has been in much demand globally but as the market open up for fresh water fish. We have already started innovative Plan for promoting and producing fresh water fish by fish cage culture. We have started to establish hygienic and modern fish markets having moderate and high potential for fisheries.


RAS Aquaculture


Recirculating aquaculture systems (RAS) are used in home aquaria and for fish production where water exchange is limited and the use of biofiltration is required to reduce ammonia toxicity. Other types of filtration and environmental control are often also necessary to maintain clean water and provide a suitable habitat for fish. The main benefit of RAS is the ability to reduce the need for fresh, clean water while still maintaining a healthy environment for fish. To be operated economically commercial RAS must have high fish stocking densities, and many researchers are currently conducting studies to determine if RAS is a viable form of intensive aquaculture.

RAS offers the advantage that temperature and other variables can be controlled, in order to maximise growth and maintain fish health. Recirculating systems also require much less incoming water, some newer plants require only approx. 1 – 5%, compared to flow through farms, minimising the discharge to the environment and allowing operations to be established even where water supplies are quite small.

TYPES OF Recirculating Aquaculture Systems (RAS)
AQUAPONICS

Combining plants and fish in a RAS is referred to as aquaponics. In this type of system ammonia produced by the fish is not only converted to nitrate but is also removed by the plants from the water.[20] In an aquaponics system fish effectively fertilize the plants, this creates a closed looped system where very little waste is generated and inputs are minimized. Aquaponics provides the advantage of being able to harvest and sell multiple crops. Contradictory views exist on the suitability and safety of RAS effluents to sustain plant growth under aquaponics condition. Future conversions, rather ‘upgrades’, of operational RAS farms to semi-commercial Aquaponic ventures should not be deterred by nutrient insufficiency or nutrient safety arguments. Incentivizing RAS farm wastes through semi-commercial aquaponics is encouraged. Nutrients locked in RAS wastewater and sludge have sufficient and safe nutrients to sustain plant growth under aquaponics condition.

AQUARIUMS

Home aquaria and inland commercial aquariums are a form of RAS where the water quality is very carefully controlled and the stocking density of fish is relatively low. In these systems the goal is to display the fish rather than producing food. However, biofilters and other forms of water treatment are still used to reduce the need to exchange water and to maintain water clarity.[22] Just like in traditional RAS water must be removed periodically to prevent nitrate and other toxic chemicals from building up in the system. Coastal aquariums often have high rates of water exchange and are typically not operated as a RAS due to their proximity to a large body of clean water.


Biofloc Aquaculture


Biofloc system was developed to improve the environmental control over the aquatic animal production. In aquaculture, the strong influential factors are the feed cost (accounting to 60% of the total production cost) and most limiting factor is the water/land availability. High stocking density and rearing of aquatic animals requires wastewater treatment. Biofloc system is a wastewater treatment which has gained vital importance as an approach in aquaculture.

The principle of this technique is the generation of nitrogen cycle by maintaining higher C: N ratio through stimulating heterotrophic microbial growth, which assimilates the nitrogenous waste that can be exploited by the cultured spices as a feed. The biofloc technology is not only effective in treating the waste but also grants nutrition to the aquatic animal.

The higher C : N is maintained through the addition of carbohydrate source (molasses) and the water quality is improved through the production of high quality single cell microbial protein. In such condition, dense microorganisms develop and function both as bioreactor controlling water quality and protein food source. Immobilization of toxic nitrogen species occurs more rapidly in bioflocs because the growth rate and microbial production per unit substrate of heterotrophs are ten-times greater than that of the autotrophic nitrifying bacteria. This technology is based on the principle of flocculation within the system.

The biofloc technology has been implemented in shrimp farming due to its bottom dwelling habit and resistance to environmental changes. Studies have been conducted to assess the larval growth and reproductive performance of shrimps and Nile tilapia. An improved breeding performance was observed in shrimp reared in the biofloc system when compared to that of normal culture practices. Similarly improved larval growth performance was also noticed.