WATER - proved GmbH plans and builds Recirculating Aquaculture Systems - for more than 10 years. 
Recirculating Aquaculture Systems (RAS) offer the possibility to produce fish and shrimp almost independent of location. 
Water parameters such as temperature, oxygen or pH-value can be kept in the optimal range for the respective fish or shrimp species throughout the year. In addition to consistently best growth and a high predictability of the production (and accordingly the marketing), this also enables the best possible utilization and use of resources.
In addition, the animals kept are protected from environmental influences and predators. By using mechanical and biological water treatment processes, only purified water leaves the system, thus limiting the environmental impact of production to an absolute minimum.

Tailormade aquaculture - not just a slogan for us, but the clear goal of our daily work.
Thus, we plan and adapt each of our systems specifically for the species kept, the respective location and its individual framework conditions.

What are the characteristics of a Recirculating Aquaculture System?

Best farming conditions, high system stability and low operating costs. Due to the continuous development of our concepts and products, we can offer you exactly that. The combination of proven and precisely selected standard components with our own "tailor-made" products result in excellent conditions for the operation of your aquaculture plant.

What species of fish can be produced in Recirculating Aquaculture Systems?

In principle, almost all fish species suitable for aquaculture can be produced in Recirculating Aquaculture Systems. This means that this question does not really arise. Much more important is the question of which market is to be served, i.e. which fish species can be sold on the market at a good price. Of course, the characteristics of the respective fish species also play a role, since the fish should naturally grow as quickly as possible and have a good feed conversion ratio. Even with an optimal design of a Recirculating Aquaculture System, the production of the fish is somewhat more expensive than in flow through systems or ponds. A detailed and extensive design of the system is therefore the first step in order to use capital as efficiently as possible later on.

The answer to the question of the right fish species can therefore not be answered in one sentence. Read more about fish species that can be produced excellently in Recirculating Aquaculture Systems here.

Click on the "+" below this text to read our assessment of the potential for different fish species.

Suitable species for production in Recirculating Aquaculture Systems

In the following, we would like to introduce you to different fish species suitable for production in Recirculating Aquaculture System and compare their advantages and disadvantages. 10 means good (or easy), 1 means bad (or particularly difficult). Our assessment refers to Central Europe. We will be happy to advise you on production in other parts of the world. Contact us here.

Rainbow trout

Trout in Recirculating Aquaculture Systems should be grown to a size of approximately 400 grams to 4 kg. Conditions are optimal in Recirculating Aquaculture Systems to achieve this weight in a relatively short time. Large fish can be processed similar to salmon and therefore offer a good sustainable alternative to the ever popular and well known Atlantic salmon.
Trout eggs can be purchased throughout the year.


Shrimp can be produced very well in Recirculating Aquaculture Systems. However, they require a certain salt content in the water compared to fish significantly more water volume / housing volume for the same production. Seedlings, so-called postlarvae, can be purchased or produced in-house, whereby in-house production can be very stable, but is associated with high costs. Especially in combination with an own seedling supply shrimps show their full potential in production. Shrimp is well known and appreciated in the market. The fresh, locally produced product is of better culinary quality than long-frozen imported goods - a great unique selling point!

Please also visit our page on shrimp systems.


Char, mostly hybrids of brook and lake char, so-called Alsatian char grow somewhat slower than trout, but often also achieve a higher market price. The optimum water temperature is around 15 °C, so char are particularly suitable for low inlet water temperatures.

Pike Perch

Pikeperch from aquaculture are now firmly established in the Central European production landscape. The fish is appreciated in the market and is known and widespread in almost all of Europe. However, there is a large amount of wild catch on the market and not only the seedling production is demanding. Also in grow out the pikeperch is and remains a difficult fish.


Tilapia is made for production in Recirculating Aquaculture Systems. The fish can be kept in relatively high densities and shows enormous growth performance. Its feed can be almost exclusively vegetable and the fillet quality is also excellent: white and without bones with a fine taste. The supply of fingerlings in Europe is not as good as salmonids, yet reliable. However, unfortunately, the fish is and remains quite difficult to market, so it does not score quite so well in the overall rating. 


It can be said without a doubt that everyone knows salmon and many love the fish. This is exactly what makes its production so interesting. The supply of fingerlings is stable, but the fish needs saltwater and the production cycle is long, which implies a relatively high risk. Many systems also show problems in grow out from a unit weight of one kilo. Especially in inland areas, we would therefore rather advise against salmon and focus on the production of large trout, so-called salmon trout.


Barramundi is a prized food fish in Asia and Australia, characterized by excellent product quality and rapid growth in high water temperatures. The seedling production of this fish is demanding. They live in freshwater but spawn in saltwater. However, there are quite a few hatcheries that are proficient in propagation and some that reliably ship fingerlings all over the world. So from the production side the conditions for this fish are very good. However, it is rather unknown in Central Europe, so strong marketing is necessary to sell the fish.


Sturgeon is a well-known fish, especially for the caviar. However, to speak of a single species of sturgeon is misleading, because many different species of sturgeon are produced in aquaculture. First and foremost is the Siberian sturgeon, followed by the Russian sturgeon. But also different hybrids, sterlet and white sturgeon are farmed in aquaculture in Europe. 
With sturgeon, the production of caviar will always be in the foreground. But the meat of sturgeon is also an excellent product. Unfortunately, the market for sturgeon meat in Central Europe is not very well developed. The fish can be produced in Recirculating Aquaculture Systems as well as in flow through systems and ponds. In practice, you often see a combination of different forms of production. Ask our experts which production method is best for you.


Whitefish are promising candidates for aquaculture in terms of their species diversity. Their product quality is excellent and with the right breeding lines very good production results can be achieved. However, the fish is still a newcomer to intensive aquaculture and its market is also regionally limited. In these markets, however, coregons have an enormous sales potential, not only because wild catches are relatively low due to the reduction of nutrient inputs in natural waters. 

Kreislauftechnik zur Modernisierung von Durchlaufanlagen

Recirculation technology also plays an important role in the modernization of flow through systems for trout, other salmonids and sturgeon. Components from Recirculating Aquaculture Systems increase the efficiency of existing systems. Read more in the flow through systems section or contact us directly.

What do I need to operate a Recirculating Aquaculture System?

Although Recirculating Aquaculture Systems (RAS) use very little water compared to flow through systems, they still need some. Depending on how efficiently the system is to be operated in terms of water use, i.e. how extensive the technical equipment is designed, an exchange of 100 to 1,000 liters of water per kilogram of feed used must be expected. This amount of water is supplied to the system and leaves it mainly as backwash water and overflow water, a small part evaporates. 

When comparing suppliers, you will always come across another indication of water exchange, namely "percent of system volume". These figures sound impressive in some cases, but unfortunately say absolutely nothing about the quality and performance of the system. Only the figure "liters per kg of feed", as we use it, makes it possible to compare intensity and performance. Low water exchange in comparison to the system volume can also mean that the system is hardly stocked or is fed only very little. 


In addition to water, an insulated building is needed in most cases, which must be heated or cooled according to the temperature requirements of the fish species. If the environmental conditions suit the fish species well, no building may be necessary. However, in this case it must be prevented that animals or other uninvited visitors can enter the system. 
Depending on the type of fish to be produced, it may make sense to process the fish in-house. Especially for fish species like trout or char, which can be processed to a variety of products, it makes sense to keep the added value in the own business.


Not to be forgotten and not to be underestimated is the staff. Operating a Recirculating Aquaculture System requires personnel who are competent in handling the animals and the technology. Remember that you need an alarm service for the system, despite all the technology and safety equipment, qualified personnel must be on the system within 15 minutes in case of emergency.

RAS Components

Each Recirculating Aquaculture System consists of various components, the optimal design and interaction of which is crucial for successful long-term operation. 

Tanks and raceways WATER proved

The detailed design of the tanks or raceways is unfortunately often underestimated.
Flow conditions adapted to the fish species are just as important as simultaneously functional tank hydraulics for optimal oxygen distribution within the tank as well as for fast and complete removal of existing solids into the mechanical cleaning system. In addition, the rearing units must be easy to control, easy to manage and easy to harvest. Furthermore, systems for automated stock handling, fish feeding or even emergency oxygen supply have to be integrated in some cases.
Besides the technical design, already the conception and composition of the tank sizes and the number of tanks is extremely crucial for the later management of the system.
Accordingly, one of the first steps of our design is the layout and calculation of an exact production and management plan of your system.

Mechanical filtration

"Particle-bound solids can be removed easily, dissolved solids only with effort." - If you let this statement sink in a bit, it is clear how important intelligent and fast solids removal is. Not only is it important to select and use a reliable drum filter, but it is also important not to unnecessarily crush the solids on their way out of the tanks and into the drum filter. 
Once filtered out of the water, we can reduce the storage volume of the backwash water through our solutions for further thickening and treatment. 
Read more about mechanical filtration options and our sludge thickening solutions here.

Biological filtration WATER proved

Fish excrete ammonium into the water via the gills as an end product of their protein metabolism. Biological filters convert the ammonium into nitrate, which is tolerated in higher concentrations than the ammonium in the water. This step of biological filtration is called nitrification, it usually takes place in moving bed filters in aquaculture. WATER - proved has developed a filter concept characterized by high degradation efficiencies, low energy requirements and a small footprint. Read more here.

In addition to nitrification, a second biological filter can be used, denitrification. If fresh water use in a system is so low that nitrate concentrations (as a rule of thumb, one can assume < 600 l/kg feed in grow out) rise above a critical level, denitrification filters are used to break down the nitrate into atmospheric nitrogen. Denitrification systems are complex because they operate in the absence of oxygen (completely contrary to all other processes in fish farming) and require an external carbon source to degrade nitrate. Moreover, the denitrifying bacteria show a strong growth, so that clogging in the filter must be avoided. Our denitrification plants run largely automated and are characterized by high stability as well as low maintenance.

Read more about the denitrifications of WATER - proved here.


To reduce the bacterial count of the holding water, to prevent the spread of fish pathogens (such as bacteria and parasites) and thus to maintain stable production conditions, we equip our Recirculating Aquaculture Systems with internal, continuous disinfection. 
A balanced microfauna is essential for any system. Therefore, all our disinfection systems, whether UV or ozone, are individually controllable and adaptable to the respective requirements. 
Read more about disinfection options here.

Degassing WATER proved

The CO2 exhaled by the fish initially dissolves in the water. In order to guarantee low CO2 levels nevertheless, this is effectively removed from the holding water by means of our customized degassing system.
Lower CO2 levels significantly improve the well-being as well as the feed intake and utilization of the fish kept, which is why the precise design and conception of this part of the system plays a key role.
Our degassing systems are particularly efficient when combined with our moving bed filters, whose special design prevents nitrogen from entering the water. 

Oxygenation WATER proved

The input of oxygen is always linked to the input of energy. The higher the water pressure, the more oxygen can be dissolved. To enable water circulation in the system, the water is already lifted. We take advantage of this energy already introduced into the water to effectively dissolve oxygen in the water. Due to the system control programmed and designed by us, only as much oxygen is dissolved in the water as is needed by the fish. 
In addition to the regular oxygenation system, an emergency oxygenation system is always available for emergencies. Read more about our oxygenation systems here.