Aquaculture

Aquaculture is the production of aquatic animals under controlled conditions. Controlled conditions includes the protection against predators and diseases, the reproduction cycle, the type and amount of feed as well as the harvest of the cultivated organisms. The versatile spectrum of cultivated species includes plants and animals, such as fish, mollusks, crustaceans, worms and snails.

A typically cultured fish in aquaculture uses only a fraction of 20 – 30% of the supplied nitrogen for its own biomass gain. In average it losses about 5% during feeding, another 15 – 20% are faecal losses and the remaining 45 – 60% are excreted into the surrounding waters.

You might get the impression that aquaculture won’t be very efficient but compared to other farmed animals aquaculture organisms convert their supplied feed very efficiently. Nowadays, feed conversion ratios of 0.8 – 1.5 are common, which means that for the production of 1.0 kg fish on average between 0.8 – 1.5 kg feed are required.

According to the FAO (Food and Agriculture Organization of the United Nations) in 2010 only Denmark, Finland and Germany were performing aquaculture in the Baltic Sea Region. The total production of the three mentioned nations within the Baltic Sea Region was 9.383 tons in 2010, and Finland achieved more than 98% of the total production (9.269).

Denmark produced around 100 tons and Germany had just a minor fraction of about 14 tons. The German aquaculture production in the Baltic Sea Region has its focus on species, which are able to tolerate lower salinities, such as rainbow trout or perch.

Aquaculture affects its surrounding environment. The main effect to the environment occurs due to the uncontrolled transfer of nutrients, such as nitrogen and phosphorus, from open production systems.

Open production systems, such as net cages or flow through systems, interact directly with the surrounding environment and use the constant water flow to provide oxygenated water for the fish.

Nutrient excretions from the cultivated fish leads to eutrophication but it is important to consider that aquaculture production compared to other nutrient sources is only a very small fraction of all the nutrients transferred to the Baltic Sea Region.

Besides the nutrient transfer aquaculture might also bear pathogens, which can be transferred from cultured to wild organisms. Furthermore, escaped farm animals might interbreed with natural occurring individuals and thereby change the genetic variability of the naturally existing stocks.

Due to the depletion of several naturally occurring fish stocks, caused through e.g. overfishing or destruction of natural habitats, some time ago re-stocking activities started to re-introduce these species, namely fish species like salmon, sea trout, white fish or sturgeon. The current development of these stocks is good but so far most of these recovered stocks do not allow normal fishing activities.