A Guide to Recirculation Aquaculture
Case story examples
Salmon smolt production in Chile Growth in the Chilean salmon production during the 90s required an increasing supply of smolts from freshwater to be stocked in cages for grow-out at sea. Smolts were produced in river water or in lakes, where the water was too cold and the environment was suffering. Introducing recirculation helped smolt farmers to produce vast amounts at a significantly lower cost in an environmentally friendly manner. Also, the optimal rearing conditions resulted in faster growth, which made it possible to produce four smolt batches per year instead the previous one batch a year technology.
· Food and Agriculture Organization of the United NationsDisease
For the innovative entrepreneur there are several opportunities in this kind of recycled aquaculture. The example of combining different farming systems can be developed further into recreational businesses, where sport fishing for carp or put & take fishing for trout can be part of a larger tourist attraction including hotels, fish restaurants and other facilities. There are many examples of recirculation systems operating without any disease problems at all. In fact, it is possible to isolate a recirculation fish farm completely from unwanted fish pathogens.
· Food and Agriculture Organization of the United NationsWaste water treatment
Farming fish in a recirculation system where the water is constantly reused does not make the waste from the fish production disappear. Dirt or excretions from the fish still have to end somewhere. Figure 6.1 Excretion of nitrogen (N) and phosphorus (P) from farmed fish. Note the amount of N excreted as dissolved matter. Source: Biomar and the Environmental Protection Agency, Denmark. The biological processes within the RAS will in a smaller scale reduce the amount of organic compounds, because of simple biological degradation or mineralisation within the system.
· Food and Agriculture Organization of the United NationsRunning a recirculation system
Figure 5.1 Water quality and flow in filters and fish tanks should be examined visually and frequently. Water is distributed over the top plate of a traditional trickling filter (degasser) and distributed evenly through the plate holes down through the filter media. Moving from traditional fish farming to recirculation significantly changes the daily routines and skills necessary for managing the farm. The fish farmer has now become a manager of both fish and water.
· Food and Agriculture Organization of the United NationsProject planning and implementation
The idea of building a recirculation fish farm is often based on very different views on what is important and what is interesting. People tend to focus on things they already know or things they find most exciting, and in the process forget about other aspects of the project. Five major issues should be addressed before launching a project: Sales prices and market for the fish in question Site selection including licences from authorities
· Food and Agriculture Organization of the United NationsFish species in recirculation
A recirculation system is a costly affair to build and to operate. There is competition on markets for fish and production must be efficient in order to make a profit. Selecting the right species to produce and constructing a well functioning system are therefore of high importance. Essentially, the aim is to sell the fish at a high price and at the same time keep the production cost at the lowest possible level.
· Food and Agriculture Organization of the United NationsThe recirculation system, step by step
In a recirculation system it is necessary to treat the water continuously to remove the waste products excreted by the fish, and to add oxygen to keep the fish alive and well. A recirculation system is in fact quite simple. From the outlet of the fish tanks the water flows to a mechanical filter and further on to a biological filter before it is aerated and stripped of carbon dioxide and returned to the fish tanks.
· Food and Agriculture Organization of the United NationsIntroduction to recirculation aquaculture
Recirculation aquaculture is essentially a technology for farming fish or other aquatic organisms by reusing the water in the production. The technology is based on the use of mechanical and biological filters, and the method can in principle be used for any species grown in aquaculture such as fish, shrimps, clams, etc. Recirculation technology is however primarily used in fish farming, and this guide is aimed at people working in this field of aquaculture.
· Food and Agriculture Organization of the United Nations