Linn-Catalogue 2019-2020

OXYGEN-ENRICHMENT-SYSTEMS Increasing demands of fish quality, higher stocking densities, declining water sup- ply and the use of high quality, expensive feed necessitate more effective oxygen transfer methods than surface aerators alone. With surface aeration, it is only possible to achieve a maximum of 100 % saturation, and then with the expense of high energy costs. This is because oxygen is only present in air at a low concentra- tion (about 20%). This is the reason why the peak demand of oxygen in many operations cannot be covered any more with surface aerators. Due to this, a situation of lack of oxygen (at least temporarily) occurs. During pe- riods of low oxygen, feed is poorly dige- sted. The fish subsist, resulting in little or no growth, and poor health. Oxygen is a very important factor in fish farming. With abundant dissolved oxygen, fish growth is maintained, food conversion rate is op- timised and less faecal waste is generated. In addition, fish health improves, and they are less susceptible todisease. Thesebene- fits result in cost savings. A ‘fish stock formula’ can be found by referring to the technical literature. From this it is possible to calculate the fish stock in kilograms per litre of intake water. The most important factor when calculating stock capacity is available oxygen and oxygen consumption per kg of feed. A simple example will readily illustrate the importance of adequate oxygen levels. Example: a pond at 250 m altitude, sto- cked with 10 cm long rainbow trout, wa- ter temperature 10 °C and a daily feeding rate of 1.5 % of the bodyweight. With a dissolved oxygen saturation of 10 mg/l (= 90 % saturated) this formula calculates a production of 1.3 kg trout per litre intake water. If the dissolved oxygen concentra- tion can be increased to 11.1 mg/l (= 100 % saturated) the production will increase to 1.7 kg trout per litre intake water. This corresponds to an increase of 30%. This example illustrates the profound effect that oxygen has on the stock of a pond, and shows very clearly the poten- tial offered by the use of oxygen with ef- fective enrichment systems. Clearly, the decision to use pure oxygen in fish-farms is cost effective because the environment for the fish can be 100 % oxygen-satura- ted all year round. LINN Gerätebau has developed specialised oxygen-enrich- ment systems for this purpose. They are used directly in the pond, usually floating like an aerator. LINN systems offer high oxygen transfer rates with high dissolu- tion efficiency. Comprehensive information and techni- cal data on the different LINN systems ap- pear on the following pages. 17 LINN