Greenwater Boosts Prawn Yield

The news is a boon to fledgling prawn farmers as it alleviates the need for a biofilter to clean the water used in "freshwater" farms, thus doing away with an extra ongoing cost in running their businesses says The Brunei Times.

A pilot study carried out by the 23 participants of the month-long "On-site training on freshwater prawn breeding and larval rearing" course found that they were able to obtain post-larvae within 25 days, with a high survival rate of 72 per cent for the "greenwater" system.

It was also found that there was a higher metamorphosis rate in greenwater systems due to factors such as favourable temperatures and water quality.

Course instructor Manuel Alban Laron frora Aquaculture Department of the Southeast Asian Fisheries Development Centre (Seaf Dec) explained that greenwater, which is 90 per cent chlorella, a type of algae, acts as a buffer for ammonia levels in the water.

"It removes the ammonia from the water and breaks down the (prawn) waste," he said, adding that the algae also provides shading for the prawn from the sun.

Mr Laron told The Brunei Times that local prawn farmers can use greenwater to lower their costs of production, if they do not intend to use a biofilter in their prawn tanks, which is sometimes a costly piece of technology for farmers.

"The greenwater minimises the need to change the water (in these tanks) and if you have large tanks, this can lower production costs," he said during the course on last week.

The course instructor said that operators can set up greenwater tanks by putting in the algae and NPK (Nitrogen Phosphorus Potassium) fertiliser into the tanks before setting up their hatcheries.

However, the success of using greenwater still depends on the specific conditions of these tanks. For the exercise, the course participants placed the greenwater system outdoors, exposing it to sunlight. The clearwater system was placed indoors.