Guide to Recirculation Aquaculture

Recirculation aquaculture is essentially a technology for farming fish or other aquatic organisms by re-using 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.

New Series

Guide to Recirculation Aquaculture

The Guide to Recirculation Aquaculture is the result of a collaboration between EUROFISH, Thomas Moth-Poulsen, FAO Fisheries Officer for Central and Eastern Europe, and Jacob Bregnballe, Akva Group, who authored the book.

The stringent environmental restrictions to minimize pollution from hatcheries and aquaculture plants in northern European countries have sparked the rapid technological development of recirculation systems. However, recirculation also secures a higher and more stable aquaculture production with less diseases and better ways to control the parameters that influence growth. State-of-the-art of the recirculation methods use far less water than conventional flow-through farms and sophisticated filtering technologies are used to treat the the water. Recirculation systems thereby offer two immediate advantages: cost effectiveness and reduced environmental impact. However, running these systems calls for additional skills and training and the hope is that the Guide to Recirculation Aquaculture will provide readers with some useful insights into the workings of recirculation systems.

The Guide will be serialised over the next issues of the Eurofish Magazine. It is also available as a hard copy from the shop on the EUROFISH webite, for EUR35.

Table of Contents

Chapter 1: Introduction to recirculation aquaculture

Chapter 2: The recirculation system step by step

Chapter 3: Fish species in recirculation

Chapter 4: Project planning and implementation

Chapter 5: Running a recirculation system.

Chapter 6: Waste water treatment

Chapter 7: Disease

Chapter 8: Case story examples

- Salmon smolt production in Chile

- Turbot farming in China.

- Model trout farms in Denmark

- Recirculation and re-stocking

- Mega farms

References & Appendix

Recirculation is growing rapidly in many areas of the fish farming sector, and systems are deployed in production units that vary from huge plants generating many tonnes of fish per year for consumption to small sophisticated systems used for re-stocking or to save endangered species.


Degree of recirculation can vary

Recirculation can be carried out at different intensities depending on how much water is recirculated or re-used. Some farms are super intensive farming systems installed inside a closed insulated building using as little as 200 litres of new water per kilo of fish produced, whereas other systems are traditional outdoor farms that have been re-built into recirculated systems using around 3 cubic m of new water per kilo of fish produced. A traditional flow-through system for trout will typically use around 30 cubic m per kilo of fish produced.

Seen from an environmental point of view, the limited amount of water used in recirculation is of course beneficial as water has become a limited resource in many regions. Also, the limited use of water makes it much easier and cheaper to remove the nutrients excreted from the fish as the volume of discharged water is much lower than that discharged from a traditional fish farm. Recirculation aquaculture can therefore be considered the most environmentally friendly way of producing fish at a commercially viable level.

Most interesting though, is the fact that the limited use of water gives a huge benefit to the production inside the fish farm. Traditional fish farming is totally depending on external conditions such as the water temperature of the river, cleanliness of the water, oxygen levels, or weed and leaves drifting downstream and blocking the inlet screens etc. In a recirculated system these external factors are eliminated either completely or partly depending on the degree of recirculation and the construction of the plant.
Recirculation enables the fish farmer to completely control all the parameters in the production, and the skilfulness of the farmer to operate the recirculation system itself becomes just as important as his ability to take care of the fish.



Fish grow better when conditions are stable

Controlling parameters such as water temperature, oxygen levels, or daylight for that matter, gives stable and optimal conditions for the fish, which again gives less stress and better growth. These stable conditions result in a steady and foreseeable growth pattern that enables the farmer to precisely predict when the fish will have reached a certain stage or size. The major advantage of this feature is that a precise production plan can be drawn up and that the exact time the fish will be ready for sale can be predicted. This favours the overall management of the farm and strengthens the ability to market the fish in a competitive way.

There are many more advantages of using recirculation technology in fish farming, and this guide will deal with these aspects in the following chapters. However, one major aspect to be mentioned right away is that of diseases. The impact of pathogens is lowered considerably in a recirculation system as invasive diseases from the outside environment are minimised by the limited use of water. Normally water from fish farming is taken from a river, a lake or the sea, which naturally increases the risk of dragging in diseases. Due to the limited use of water in recirculation the water is mainly taken from a borehole, drainage system or spring where the risk of diseases is minimal. In fact, many recirculation systems do not have any problems with diseases whatsoever, and the use of medicine is therefore reduced significantly for the benefit of the production and the surrounding environment.


Some farms are super intensive farming systems installed inside a closed insulated building using as little as 200 litres of new water per kilo of fish produced.
Traditional outdoor farms that have been re-built into recirculated systems use around 3 cubic m of new water per kilo of fish produced.

Recirculation systems call for new skills

Aquaculture is not for everyone; it requires knowledge, good husbandry, persistence and sometimes nerves of steel. Shifting from traditional fish farming into recirculation does make many things easier, however at the same time it requires new and greater skills. To be successful in this quite advanced type of aquaculture calls for training and education for which purpose this guide has been written.