Nieuws - 26 april 2001

Model provides picture of nitrogen content in fish ponds

Model provides picture of nitrogen content in fish ponds

A research tool, a computer programme for managers and an environmental tool; Ricardo Jim?nez-Montealegre's model is versatile to say the least. The recent PhD graduate developed a predictive model of nitrogen processes and balances in a much-used type of fish pond.

Fish farming researchers have long known that only thirty percent of the fish feed actually makes it to the fish. The rest just floats around in the pond. Micro-organisms in earthen ponds can transform the protein remains into poisonous substances which may inhibit growth of the fish or even kill them. Much of the fish feed just goes to waste. Environmental groups are also expressing increasing concern about the waste water from fish ponds that is released into the environment. This is a growing problem, as aquaculture activities are currently expanding at the rate of ten percent each year.

Optimising model

The new model can help fish pond managers to optimise the use of fish feed, so that they can raise more fish with less food, and also reduce their discharges. By entering a number of values, such as temperature and oxygen content of the water, the model indicates where the nitrogen in the pond is located: in uneaten fish feed, in the bodies of the fish, in excreta, in the water or in the soil at the bottom of the pond.

Jim?nez-Montealegre has now returned to Costa Rica and is working on refining the model to make it more user-friendly. He received his PhD on 18 April, and was supervised by Professor Bram Huisman and Professor Johan Verreth, both of the Fish Culture and Fisheries Group.

Willem Koert