Aquaculture has expanded to become a significant global industry and a reliable supply of food, as our oceans has become overfished. From just 7% of all seafood consumed in 1974 to over 44% now, the aquaculture business now provides the majority of the seafood.
Water quality monitoring and dissolved oxygen (DO) testing are crucial for aquaculture sector, which is expected to grow to billions in value over the next years. Aquaculture businesses must maintain accurate DO levels in their aquatic ecosystems, if they want to produce healthy, consumer-safe, and market-ready seafood—or face dire consequences.
What is the value of Dissolved Oxygen in Aquaculture?
The necessity of oxygen for terrestrial life is well known, but it also has a significant impact on aquatic ecosystems. Although, fish don't have lungs, they nonetheless need a little amount of oxygen to breathe and do other basic tasks. They obtain the dissolved oxygen, or DO, found in the water surrounding them, which is essential for their survival.
Aquatic plants, kelp, and algae that live at lower depths have adapted to use a tiny quantity of sunlight, to carry out photosynthesis at greater depths, in contrast to plants that float on the water's surface that release oxygen into the atmosphere. These organisms in deep waters release oxygen into the water. At the water's surface, it is also dispersed into the water from the atmosphere.
Importance of Dissolved oxygen for aquatic life and aquaculture
The amount of oxygen in the ocean and other natural water sources is normally measured in parts per million, and is significantly less than that in the atmosphere. The majority of fish only need DO concentrations of five ppm or more to survive. However, bigger fish require more oxygen than smaller fish, and the quantity and variety of plants and animals present can affect DO levels within a single aquatic ecosystem.
For instance, 3 mg/l of DO is the ideal quantity for shrimp culture. For intensive aquaculture, values higher than 5 mg/l are advised.
Although five ppm may not seem like much, DO depletion can have very negative impacts. Lack of oxygen resources makes fish more susceptible to illness and infection, less effective at converting food into energy, and less able to grow properly. They will eventually perish if oxygen levels drop below a particular point.
High DO levels in water
Very high levels of DO are typically the result of extensive plant photosynthesis. Fertilizer runoff frequently leads to significant uncontrolled plant growth, particularly algal bloom, which can be harmful to aquaculture.
Low DO levels in water
Low DO levels in water have a wide range of causes. In aquaculture, overcrowding or overfeeding fish in a tank or enclosure submerged underwater is the most frequent source of low DO. More fish and more food inevitably means that more oxygen is required every day, since fish need oxygen to convert the food they eat into fuel. DO levels will plummet if oxygen isn't being enough replaced by organisms, which photosynthesize or at the water's surface. To maintain acceptable DO levels for greater fish populations, many aquaculture facilities may introduce photosynthesizing aquatic organisms into a farming setting.
Effects of zooplanktons on dissolved oxygen (DO)
Zooplankton booms and phytoplankton crashes are two additional frequent causes of low DO levels.
While, zooplanktons are respiring organisms that primarily depend on phytoplankton and are known to proliferate quickly during phytoplankton blooms, phytoplankton is a photosynthesizing species that produces oxygen.
An abundance of zooplankton can reduce the quantity of DO accessible to other organisms, in the same aquatic habitat by devouring phytoplankton and using it to respire and turn food into energy.
Some natural phenomena can also result in phytoplankton crashes!
For instance, persistent cloud cover or other impediments might prevent sunlight and wind from reaching an area, which can kill off certain phytoplankton species and cause DO levels to drop.
The pH can also have an impact on DO levels!
The amount of DO that water can carry and transmit can alter depending on how the pH value is changed. Do frequent pH readings to check whether the two metrics are related, as you try to determine the cause of fluctuations in DO.
Identifying fish that are affected by low DO levels
Fish that are affected by low DO levels may appear lethargic and spend more time slurping air, at the water's surface or in front of an aerator. They might also show signs of losing their appetite. Larger fish will experience oxygen depletion before smaller fish and other creatures in the same habitat, because they need more oxygen to thrive. They might also exhibit signs of low oxygen levels more quickly.
Checking the level of DO
Fish keepers and aqua culturists should routinely check the DO levels in their tanks, using portable or inline DO controllers, transmitters, or analyzers. Monitoring fluctuations in DO levels allows you to spot when levels are at risky lows, and make necessary changes to your aquatic habitat to boost the oxygen content.
Raising the DO in water
There are many things you may take to increase DO levels in your aquatic environment, if your water quality sensor shows low DO levels. They consist of:
· increasing oxygen production by introducing photosynthesizing organisms into the environment,
· artificial aeration equipment being used more frequently or vigorously to aerate the water,
· spraying water on your enclosure or tank's surface to promote surface-level oxygen diffusion,
· limiting intake to lower oxygen consumption,
· removing aerobically decomposing animals, plants, and other dead matter,
· introducing new water with a higher DO content to replace the water in your surroundings.
If you regularly check the DO levels, you ought to be able to make any necessary adjustments, without having to resort to more drastic procedures like replacing the water.
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