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Water quality in aquaculture

Each organism living in water has factors influencing its comfort; it can be called the water quality. Critical for fresh-water fish breeding in aquaculture are water temperature, oxygen level and volume of other gases in the water, the level of pollution (hard particles and dissolved substances), pH level, microorganisms and pathogens.

A balance forms in natural water bodies (rivers, lakes, ponds) without assistance – the water quality complies with the needs of animals living in the water body; or, speaking more precisely – only the animals satisfied with the quality of water live in the said water body.

If a human decides to meddle with an already existing ecosystem or create a net one, the quality of water must be controlled and sustained artificially. The higher the population of the water body, the more drastic the reaction to the change of water quality is.

Oxygen in water

The dissolved oxygen is measured in milligram/litre (mg/l) or as a percent of the maximal possible level in that water temperature. Different fish species have different requirement for water quality.

Different fish species have different requirements regarding oxygen levels also. Fish can live in water with low oxygen levels, but their growth and development will be much slower or it might even stop.

The oxygen volume in water is affected by plants that absorb carbon dioxide and release oxygen during photosynthesis and by the wind that touches water. If needed, the water can be supplied with oxygen directly or with other air. That can be achieved using aerators or air diffusers. It is important to supply oxygen as small bubbles.

Click here to read more about aerators and water aeration in winter.

Other dissolved gasses

Carbon dioxide (CO2)

Carbon dioxide is another significant indicator of water quality. If there is too much CO2 in the water, the fish have problems excreting it from their organisms and haemoglobin in their blood loses its capability to transport oxygen, so the fish experience stress similar to suffocating. Plants consume CO2 but only when exposed to light.

Ammonia nitrogen

Even small volume of free ammonia in water is highly toxic and deadly to fish. Effective filters and biological water purification systems are vital for ensuring the water quality in intensive breeding systems with water recirculation. Effective filtering and active bacteria will maintain safe levels of nitrite concentration.

Click here to read more about filters for hard particles discharging ammonia.

pH level

The balance between the tocic NH3 and non-toxic NH4+ is regulated bu pH level of water. NH4+ <-> NH3 + H+
pH shows the number of hydrogen ions in aqueous solution, or in other words – it shows how acidic or alkaline the water is. A pH less than 7 is said to be acidic and solutions with a pH greater than 7 are basic or alkaline and pH 7 is neutral. Different fish species, organisms and plants have different requirements regarding pH level of water. In aquaculture pH level should usually be between 6.5 and 8.5.

Water quality is affected by the pH level so it should be controlled in aquaculture. In ponds the pH level will be affected by the proportion between the amount of water plants and fish. The more fish live in the water the more CO2 they excrete and the more acidic (pH level goes down) water gets and the other way around – the more plants, the more oxygen, the higher pH and more alkaline water. pH level will differ depending on the time of the day.

pH level can be measured with pH meters or indicators. pH meters are electric devices that show the pH result of a solution instantly on a readable display. Indicators are halochromic chemical compounds added in small amounts to a solution and change the colour depending on the pH level. The colour of the solution can then be compared to standard pH level colour palette to indicate the pH level of the water.

Water temperature

Water temperature is a significant indicator of water quality in aquaculture. The optional temperature differs by the fish species living in it. The temperature affects both the organism of the fish itself and the surrounding environment. Lower temperatures slow down the metabolism of fish and they don’t eat and don’t grow. Too high temperature will cause stress levels to rise. The higher the water temperature the less oxygen dissolves in the water and the more gasses containing nitrogen emit, which in turn decreases the quality of the water. If the water temperature is higher than the optional one for the certain fish species, feeding the fish should be avoided.

Hardness of water

Hardness of water is another indicator of water quality. Fish and planktons eaten by them favour calcium and magnesium compounds. Hardness of water is measurement of overall solubility of salts. Solubility is usually given in CaCO3 or CaO mg/l. 0.75 mg/l is considered to be soft, 0.76-150 mg/l is hard and over 300 mg/l is very hard water. Hard water rarely is harmful to fish.

Hard particles in water

Water quality also means that water has to be clear and not turbid. Turbidity is caused by small pieces of matter (hard particles) floating in the water, and when the fish filter the water through gills, the particles block the gills. The hard particles can be dust that lands in an open body of water, part of the ground of the water body or faeces and uneaten feed. Larger pieces such as leaves and fallen branches do not create a physical barrier, but when they drown they will emit carbon dioxide and nitrogen.

In basins and recirculation systems the hard particles are removed with the drum filters – fine rotating filter plates (that are similar to drums) through which the particles are separated from the flowing water. In open bodies of water though which flow other brooks, the larger physical objects (leaves) are removed using the rotating leaf screeners which work autonomously and take them out on the shore.

Click here to read more about filters for the small hard particles.

Click here to read more about leaf screeners.

Water disinfection

Water quality can’t be considered to be satisfactory if there are pathogens in the water. Preventive actions are the only way to fight diseases in open bodies of water. It includes avoiding contact with other bodies of water (don’t carry boats or fishing gear from on body of water to another), disinfecting the pond, for example, you can disinfect empty ponds using lime. When moving fish from one basin to another they can be passed through low concentration salt water.

For constant water disinfection devices of ultra-violet light can be used.

Tested and approved are ultra-violet light devices made by UltraAqua. Read more about them on http://www.ultraaqua.com/


Aquaponics is the combination of aquaculture (raising fish) and hydroponics (the soil-less growing of plants) that grows fish and plants together in one integrated system. Plants are fed by the water that fish live in. Both sides benefit from such arrangement – fish emit ammonia that are transformed into other nitrogen compounds by bacteria, and phosphorous compounds accumulate in water. Both nitrogen and phosphorous compounds are used by plants for growing. Plants grown in this system will be completely biological and the overall expenses will be lower than when growing plants and fish separately.

We can develop an aquaponics system using heat-preferring fish and using the solar energy.