IMPACT OF FISH FEED ON AIRLIFT PUMP PERFORMANCE

Airlift pumps are commonly used in aquaculture systems to pump water, mix water and maintain critical gas levels. In a production sablefish system, a significant decrease in airlift pumping rate was observed immediately after feeding. This decrease in flow could negatively impact water quality, system performance, and fish health. A three-part experiment was conducted to examine the impact of feed addition on airlift pumping rates. All tests were conducted in 2" PVC pipe with a submergence ratio of 69%. The first experiment tested diffuser injection and direct air injection airlift pumps in a high-density marine sablefish rearing system (75 kg/m³) fed 1.3% of body weight, three times a week. This feed was a fish-based brood feed (BioOregon, 48% crude protein, 20% crude lipids). A second experimental system was developed to assess the time response and concentration impacts of known additions of BioOregon on pumping rates in both fresh water and seawater but without fish. The last experiment was similar to the second experiment but a wide range of larval fish feeds, fish-based production feeds, and plant-based feeds were evaluated.

In the rearing system, feeding resulted in a 50% in pumping rate following feeding. The pumping rate gradually increased over the day (Figure 1). Repetitive feed additions (up to 10 mg/L) in seawater reduced the pumping rate by up to 80% for the diffuser but only 10% for direct air injection. Video footage revealed increasing bubble coalescence with the addition of feed. The decrease in pump flow is likely due to compounds leaching out of the feed that change bubble size. Further research is needed to understand what type of compounds are responsible for the decrease in pumping and how the water flowrate changes for a wider range of airflow rates.