Stay in control of oxygen fluctuations

In fish farming, large fluctuations in the oxygen content of water have a negative impact on the well-being of the fish and consequently on its growth. High water temperatures or rich vegetation in the water are important alarming factors to observe, especially in summer periods.  

Oxygen saturation for economic growth 

The oxygen content of water is affected by many different parameters, in particular temperature, day-night variations, air pressure, feeding, size of fish and stress levels. Economic growth rates are only possible when these variations are taken into consideration. 

Trout for instance generally require a relatively high level of oxygen supply as they consume between 0.3 and 0.5 kg of oxygen for every 1 kg of feed to be digested. In traditional trout farming, for the needs of the trout to be adequately met, the recommendation is to keep the oxygen saturation level at 100 % as it enters the fishpond and that it should still be at least 70 % at the outlet.  

100 % oxygen saturation means that the water contains approx. 14 mg of oxygen per litre at 2 °C and only approx. 9 mg at 20 °C. In practice, the saturation level at the inlet is often different, especially if the farm is run on surface water, for instance due to high summer temperatures or to rich vegetation. 

 

Impact of oxygen on FCR and growth 

The negative consequences of fluctuating oxygen levels on feed conversion call for oxygen control. A low oxygen content without oxygen enrichment leads to an unsatisfactory FCR, while oxygenation results in a good FCR and faster growth. In a trial run in summer, a traditional trout farm taking its inlet water from a stream with ample vegetation was divided into one section with and one without oxygenation. Using a 24-hour oxygen-measuring device with one probe in the inflow and another probe in the outflow, readings of the oxygen content were taken every 10 minutes.  

Oxygen levels in the trial 

The oxygen saturation level in the inlet to the farm fluctuated very much. At night, it showed out to be even lower than the minimum of what it should be in the outflow for the needs of the trout to be adequately met. In the section with no oxygenation the outlet water was very unsatisfactory throughout most of the trial period, especially at nighttime. In the section with oxygenation, the outflow values were balanced out by enriching the water with oxygen. It was clearly demonstrated that the outflow values could be kept at an optimal level by oxygenating the water from 4pm to 8am (16:00-08:00). 

FCR and growth – trial results 

In the section of the fish farm with no oxygenation, the FCR in the trial period was 1.04; the daily growth was 0.80 %. In the section with oxygenation, in contrast, the FCR was 0.86 and the daily growth was 1.30 %.  The fish in the section with oxygen regulation needed 19 % more oxygen. This meant that 30 % more feed could be given, which in turn led to increased growth. This is a clear indication of how important the oxygen supply is in terms of commercial production.