Shrimp Farms Turning Toxic Waste into Fish Food

Fish feed wastage and its impact on water-bodies are a major source of worry for the fisheries industry. The accumulation of waste leads to toxicity in farmed species.

High quality protein is essential for shrimps to grow fast. They require 45 percent quality protein in the supplementary feed. This makes shrimp feed costly and accounts for more than 55 percent of the operational cost.

Researchers at the School of Industrial Fisheries, Cusat, led by director Madhusoodana Kurup have developed a biofloc technology (BFT) that could revolutionise the aquaculture industry. With BFT, the waste which accumulates in the pond bed is converted into biofloc as a natural food. With this the carbon-nitrogen ratio is maintained at optimal levels, and inorganic nitrogen is immobilised into bacterial cells which serve as feed for shrimp.

"We screened five types of locally available carbohydrates as carbon sources for C:N ratio maintenance and among them tapioca was found the most efficient in shrimp farms,'' said Kurup.

The biofloc technology developed by the team for shrimp farming is useful in reducing the protein content of conventional shrimp feed from 40 percent to 25 percent without compromising on growth and production. He said that the biggest advantage of BFT is that farmers are benefited economically since 25 percent of diet with carbohydrate addition to the water column results in a 54 percent higher revenue per hectare.

The required dietary protein level of shrimp feed can be substantially reduced by carbohydrate addition to the water. This makes farming more economically viable and profitable.

It will also help to reduce the concentration of toxic inorganic nitrogenous products like ammonia and nitrite and reduce nitrogen discharge into open waters thus making shrimp farming ecologically more sustainable and environmentfriendly.

The team has also developed a larviculture technology for the giant freshwater prawn Macrobrachium Rosenbergii using biofloc technology.

"Development of biofloc technology is crucial in order to reduce the over dependence on fish meal produced from trash fish, which is showing an alarming depletion in our oceans," he said.

Kurup will be presenting the findings of the research at a special session on biofloc technology during World Aquaculture 2009 to be held from May 25 to 30 in Mexico.