The availability of oxygen is one of the most important water quality parameters in aquaculture, and in intensive culture systems oxygen is added to the water to reduce overall water requirement and ensure adequate oxygen availability.
It is important to maintain dissolved oxygen (DO) concentration at levels that are sufficient to support the metabolism of the fish, and maximize growth.
This issue was addressed in a paper presented by Christian Beuvard at the Aquaculture Europe
conference held in San Sebastián, Spain, last year. Beuvard, a PhD student, and his professor Helgi Thorarensen, from the Hólar Agricultural College (www.holar.is), Sauðárkrókur, Iceland, described a study that examined the long-term effects of DO concentration on feeding, growth and metabolism of Arctic charr (Salvelinus alpinus), and determined the concentration needed for optimum growth. Clearly, providing more oxygen than is actually required, simply increases costs.
Experiment set-up
Before the experiment commenced the fish were given 15 days to acclimate to the tanks and rearing conditions, water temperature of 9°C, salinity 15‰, and a 24-h continuous light regime. Arctic charr (67.4±9.7g) were reared at five different levels of oxygen saturation (61±0.9%, 79±0.9%, 98±0.7%, 122±1% and 143±0.9%). Each treatment was tested in four tanks.
Fish were fed dry pellets every day except Sundays. The fish were weighed and measured individually at the beginning of the experiment and then twice more until the experiment was terminated after 61 days. A weighed amount of feed was presented daily and uneaten pellets were collected in a feed trap and counted. This information was used to estimate the total feed intake of the fish. Feed conversion ratios (FCR) and specific growth rates (SGR) were calculated.
Oxygen consumption was measured by turning off the inflow of water into the tank for 30 minutes while measuring oxygen concentration in the water. Active metabolic rate (AMR) was measured in fish forced to swim by chasing them while oxygen consumption was measured.
Finding the optimum
The final size of the Arctic charr was not significantly affected by O2 saturation between 60 and 140%, indicating that the optimum concentration for growing this species is no higher than 60% saturation and is thus lower than for species such as Atlantic cod, spotted wolf-fish, sea bass, and Atlantic halibut.
Other studies have found the same trend where higher DO concentrations had no impact on growth. In contrast to growth performance, both active- and routine metabolic rates increased significantly with increasing oxygen saturation.
Beuvard suggests this has important consequences for the optimization of Arctic charr production, especially in Iceland where the total production in 2011 was about 3500 tonnes.
For more information email Christian Beuvard at: christian@mail.holar.is
– David Scarratt
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