Introduction Production of shrimp started a while ago in a very extensive way. Wild postlarvae were stocked in ponds and natural production in the ponds provided for the nutrition of the shrimp. To increase the production per ha, stocking density was increasing and artificial feeds were developed to complement the natural production. As technology and feeds improved, production per ha increased, but also the limits to the system became clear. Shrimp differ in a lot to other farmed species: · Shrimp are benthic. They only use the bottom of a pond. Shrimp must find the feed by chemical attraction (olfactory sensors). Feeds should leach substances (often useful nutrients) to attract shrimp to the feed. Typically, shrimp feed pellets will stay in the water for 15 - 60 minutes before the shrimp consumes them. But they can lie in water for several hours before consumption and should remain water-stable during this time. During this time, feed pellets swell by taking up water and water-soluble nutrients leach out of the pellets. These nutrients are a loss. In semi-intensive farming, shrimp are typically fed 3-4 times/day. This worsens the problem enormously. Shrimp are external masticators, meaning that they chew their feed outside their mouth. They are selective feeders, nibbling on pellets and only consume more feed when palatability is OK: When shrimp start consuming feed, they will not ingest the feed at once. They will nibble on it, select the palatable pieces and throw away whatever they don’t like. The uneaten parts are left and will be digested on the pond bottom by bacteria. Shrimps are poor digesters. Their digesting system is rudimentary. A lot of nutrients pass their system without being assimilated. For example, the protein efficiency of shrimp is only 15-20 %. In nature, shrimps will consume a lot of pre-digested feed, like rotten fish and detritus. Whatever is not assimilated goes back to nature and is recycled. In ponds however, as density of production increased, these excess nutrients became pollutants, using oxygen and degrading into ammonia, hydrogen sulphide and methane, all toxic to shrimp. To get rid of those pollutants, water is exchanged and the pollutants are flushed out of the system. This way, the chance of recirculating them is lost and the feed will never be utilised at this maximum. This is the main reason why feed conversions in shrimp culture are horribly high and don’t show any progress during the last couple of years. Shrimps can consume detritus actively or passively. Soluble nutrients will dissolve in the pond water and feed the natural bloom of the pond: phytoplankton, which in turn will feed zooplankton. The shrimp will ingest some of this plankton again. This is what we call natural production of the pond. Crustaceans have some unique nutritional requirements such as phospholipids, cholesterol, Phosphate to Calcium ratio. Knowledge of shrimp nutrition has increased during the years, but application in business has been difficult. Semi-intensive farming is not the system that will maximise shrimp efficiency and different shrimp feed qualities have not show substantial differences in the production. Hence, shrimp producers tend to choose the cheapest feed. Feeding an animal means giving the animal the nutrients it needs. The first aim should be that the nutrients are actually ingested by the shrimp. As a result a lot of effort has been made to make water stable pellets, which can stay “intact” in water for several hours without falling apart. However, it is not because the pellets seem to be intact that they actually are. Pellets absorb water (plus the salt minerals with it) and water-soluble nutrients (vitamins, amino acids and peptides, ions) will leach out. To maximise nutrient re-utilisation, we have to reduce water exchange. This can be done is different ways: One main factor is aeration instead of water exchange. The nutrient recycling can be done in the same tank of in another tank or pond. What could be called biological treatment of the pollutants would be similar to what would happen in nature, meaning bacterial flocks and substrates for nitrification. Shrimps can passively ingest and digest some of those bacteria and would graze on the substrates to supplement feeds. Nutrient recycling is then a reality.