Chapter 2: The 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. This is the basic principle of recirculation.

Sturgeon stocks are threatened worldwide by extinction. Various factors have led to a dramatic drop in populations during the last two decades. Since aquaculture can make a considerable contribution towards saving wild sturgeon and satisfying demand for “black caviar”, Aquatir Ltd decided in 2005 to build a modern recirculation system for farming sturgeon.

Chapter Two: The recirculation system step by step (continued)

Mechanical filtration

Mechanical filtration of the outlet water from the fish tanks has proven to be the only practical solution for removal of the organic waste products. Today almost all recirculated fish farms filter the outlet water from the tanks in a so called microscreen fitted with a filter cloth of typically 40 to 100 microns. The drumfilter is by far the most commonly used type of microscreen, and the design ensures the gentle removal of particles.

The vision for the future of European freshwater aquaculture – and the research and innovation needed to supports its key strategies - will be the focus of the first of a series of thematic workshops organised by the EU Aquainnova initiative. The workshop will be held in Warsaw, Poland at Sofitel hotel, from June 15-16, 2011.

Chapter Two: The recirculation system step by step(continued)

Chapter Three: Fish species in recirculation

A recirculation system is a costly affair to build and to operate, 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 of the production is to sell the fish at a high price and at the same time to keep the production cost at the lowest possible level.

Chapter Four: Project 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.

The possibility to protect oneself against financial losses through an insurance policy is not new and is practised in almost every area of life. Many aquaculture companies choose to do without this risk insurance however because they feel the requirements are too high, the procedure too complicated or the premiums too expensive. But taking out insurance in the aquaculture sector can definitely be worthwhile and should be a part of risk management.

Chapter Five: Running a recirculation system

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, and the task of managing the water and maintaining its quality has become just as important, if not more so, than the job of looking after the fish.

Chapter Six: Waste 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. The biological processes in the system will to a certain extent reduce the amount of organic compounds, because of simple biological degradation or mineralisation within the system. However, a significant load of organic sludge from the farm will still have to be dealt with.

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