The abundant availability of water resources makes Nepal a country with the potential for fish farming. Fish farming is sustainable and environment friendly cultivation practice, generally raised naturally in fish tanks or artificial enclosures. The commonly cultivated breeds are Silver carp, Bighead carp, Grass carp, Rohu, Catla, Mrigal, and Rainbow trout. Fish, being an important source of food, low in cholesterol and rich in protein, the demand of it is constantly increasing.
Introduction of the Farmer:
System of cultivation: Bio-floc system
Species: Common carp
Cost: 45,000 to 50,000 per tank
Bio-floc technology is the blue revolution in aquaculture & new technique of enhancing water quality & utilizing feed wastes in the aquaculture system. It follows the concept of conversion of ammonium in addition to organic nitrogenous wastes into bacterial biomass where heterotrophic bacterial growth is stimulated & nitrogen uptake through the production of microbial proteins is promoted by the addition of carbohydrates to the pond. Nitrogen generated by uneaten feed and excreta of cultured organisms is converted into proteinaceous feed available for those same organisms. It is a method of high density farming system.
Outer frame/net is made up of 8mm rod. Diameter of the tank is made according to the requirement, height 1 meter from the ground level. Tank of 4 dia. contains 10,000 litre of water. Similarly tank of 3 dia. contains 5,000 lit of water. Tank is internally covered by a sheet of tin. Then, covered by tarpaulin. Usually 650 GSM(gram per square meter) tarpaulin is used in bio-floc tank setup. Aerators are placed using a nylon rope. Draining pipe is set up at a slope of 5 cm from the edge towards the centre.
In bio-floc system, water is prepared by mixing different elements is accurate quantity for the proper development of organisms in the pond.
- Probiotics = 10 g bacteria/1000 lit water
- Raw salt = 1 kg raw salt /1000 lit water
- Molasses = 100 gm/1000 lit water
All of these are added in the tank. Properly aerated and kept for 3-4 days. Bacteria develops in the tank and the water appears slightly dirtish green.
Different factors like temperature, pH, dissolved oxygen, organic loading rate, etc. influence the floc formation in the pond so, these parameters are essential in order to manage the fish farming through bio-floc system:
- Total Dissolved Solid (TDS) = upto 2000 ppm
- PH = 6.8 to 8
- Ammonia = must be 0
- Temperature : 27°C – 32°C
Usually floating feed containing 32% protein is recommended for bio-floc technology. Four percent of the total fish weight is given each day. Feeding habit of fish is observed by using floating feed. Similarly, bacteria needs lot of available food, therefore the pond must be loaded with organic residues & the pond should be fully aerated (needed for proper fish growth).
Use of bacteria:
- Lactobacillus: increase fish digestibility to feed and stimulate fish growth
- Nitrifying bacteria: consumes ammonia to produce nitrites
- Heterotrophic bacteria: assimilate inorganic N waste into biomass.
Advantages of Bio-floc Technology:
- BFT is an eco-friendly culture system and it reduces environmental impact.
- It improves land and water use efficiency.
- Zeroes water exchange.
- Ensures higher productivity and promotes higher biosecurity.
- It reduces water pollution and the risk of the introduction and spread of pathogens.
- It reduces the utilization of protein-rich feed and the cost of standard feed.
Disadvantages of Bio-floc Technology:
- BFT requires increased energy requirement for mixing and aeration.
- It has reduced response time by elevating water respiration rates.
- It requires a start-up period.
- It requires alkalinity supplementation.
- This leads to increased pollution potential from nitrate accumulation.
Conclusion & Recommendation:
BFT (Bio-floc technology) will enable aquaculture to grow towards an environment-friendly approach and biosecurity. The microbial community can rapidly dissolve nitrogen leached from fish feces and uneaten food & convert it into microbial protein, maintaining water quality. Consumption of microorganisms in BFT reduces feed conversion rate (FCR) and finally lowers the farmer`s costs in the feed. It is more profitable than conventional fish farming as well as ensures more production even with low feed input. This technique is highly suitable in urban areas where there is scarce land & water but advanced technology.