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Water-saving fish farms

Fish farming is strongly dependent on the natural environment. Indeed, the water used for farming is taken from nature and subsequently returned. A pilot trout farm capable of reducing water requirements by 90% was set up at the INRA Experimental Fish Farm in Monts d'Arrée (Peima), in collaboration with the INRA SAS (Agricultural Soil and Spatialisation of Water Systems) and SCRIBE (Fish Physiology, Biodiversity and the Environment) Joint Research Units. This system may be of potential value to European fish farming that is less environmentally-dependent in the future.

Installation d'un pilote d'élevage de truites en circuit recirculé à la PEIMA (Pisciculture Expérimentale Inra des Monts d'Arrée), INRA Le Drennec 29450 SIZUN.. © INRA, MAITRE Christophe
Updated on 06/10/2013
Published on 10/12/2011

In a standard, open-circuit fish farming system, the water supply is taken from the natural aquatic environment, crosses through the rearing ponds and is then returned to the environment. This type of fish farming raises several problems linked to the large quantities of water used. The high throughputs of waste water and the considerable dilution of matter to be treated means it is technically difficult to purify the water from such farms. A large proportion of soluble wastes, such as the ammonia and phosphorus produced by the fish in rearing ponds, is thus emitted into the natural environment. The extraction of water from rivers also poses problems regarding the free circulation of migrating salmonids (salmon, brown trout, etc.) at certain periods. Finally, open-circuit farming systems remain highly dependent on the quality or availability of water, which may be deficient during a drought. The rearing of salmonids (salmon, trout, whitefish, etc.) in farms is indeed subject to stringent environmental constraints laid down in European Directives (EU Water Framework Directive 2010-2015 and LEMA).

In order to comply with this regulatory framework and offer an alternative to open-circuit fish farming, INRA has developed a system for salmonid farming based on the recirculation of water, the aim being to control interactions between farmed fish and the aquatic ecosystem.


Farming high-quality fish at lower economic and environmental costs

In this experimental system, 90% of the water is recycled by means of a system that involves re-injection of the water, after treatment, into the rearing ponds. In this way, only 10% of the amount of water necessary is extracted from the natural environment. Before the water leaving the ponds is pumped back into the circuit, it is filtered to treat the toxic substances produced by the animals: solid waste (matter in suspension) is eliminated by mechanical filtration, ammonia is transformed into nitrate by biological filtration and dissolved CO2 is evacuated via an air injection system. The low flow rate of waste water from the circuit facilitates the treatment of waste before it is emitted into the natural environment.

The aim of the pilot plant set up at the INRA Experimental Fish Farm in Monts d'Arée is to define the conditions for the viability and equilibrium of this production system, assessed using several criteria: reduction in water needs and waste, maintenance of zootechnical performance, fish welfare, fish flesh quality and the preservation of production potential.

Successful early results

The early results showed that in operating mode, the pilot was able to maintain a permanent stock of 2 tonnes of fish, equivalent to an annual production of 7 tonnes of salmonids, thus exceeding the initial target by 20%. The amount of "new" water required to achieve this yield was only 7 m3 per kilo of fish produced, versus 100 m3 under an open system. The quality of the water in the circuit was always compatible with the rearing of salmonids.

Zootechnical performance was compared with that of rainbow trout reared in a standard, open-circuit system. The results were more than encouraging. Indeed, they showed that not only was the zootechnical performance of the animals not degraded, but it was improved. After 10 months of operation, fish produced under the recirculated system were 30% fatter than those from the open-circuit system. Finally, from the health point of view, no bacterial or parasitic diseases occurred during trial.

Scientific contact(s):

  • Laurent Labbé Pisciculture expérimentale Inra des Monts d’Arrée (Peima) 29450 SIZUN

Research to be pursued

Numerous points still need to be clarified, and particularly the impact of this new rearing system on the physiological functions of fish, the quality of their flesh and their welfare. Problems with acclimatization to the environment, behaviour and responses to stress may indeed occur because of the increased number of fish in the ponds.

These analyses will focus in particular on:

  • fish health, behaviour, morphology and growth as a function of the different aquatic parameters modulated by the recirculated rearing system,
  • the characteristics and reproductive performance of fish, such as age at puberty, gamete quality and embryonic development,
  • the impact of rearing conditions on carcass quality and flesh quality.

Finally, an environmental analysis will be made of the system using tools such as Life Cycle Analysis (LCA).