Physical factors in the environment

Monitoring water and filter quality is of vital importance to ensure that the animals do not have to function at the limits of their adaptive capacity. Zebrafish will tolerate a wide range temperatures. However, exposure to temperatures at either end of the range will impact all kinds of physiological functions, because the energy expended to survive extreme conditions cannot be allocated towards other processes. This can lead to increased disease susceptibility and lower reproductive rates, so the metabolic cost of extreme conditions is high. Zebrafish are able to function under various physical conditions. The range of relevant physical parameters is shown in the table below. The laboratory should strive to attain optimal values for these physical parameters. Feeding and stressful events can create peaks (nitrite, nitrate, ammonia) and troughs (oxygen) in the values of some of these parameters. For this reason, it is important to maintain safe margins and stay well away from the limits of the tolerated range. The monitoring frequency listed in the table is but a guideline and depends on the degree to which the system is stable and how well it is managed.

Parameter [monitoringfrequency]


Water temperature [continuous; daily]

26-28.5 degrees Celsius; usually 28-28.5 degrees Celsius

pH value of the water [continuous; daily]

Recommended pH: 7-8; certainly not below 6 or above 8

Water hardness [monthly]

50-150 mg/L CaCO3

Water conductivity [daily]

250-600 μS/cm

Salinity [daily]

0.25-0.75 (ppt Knudsen)

Ammonia; nitrites; nitrates [daily; weekly]

Ammonia:<0.02 ppm (0.02mg/L); nitrites: very strict: less than 0.1 ppm (0.1mg/L); nitrates: less than 50 ppm (<50 mg/L)

Dissolved oxygen [continuous; daily]

>6 ppm (6 mg/l); >7 mg/L is recommended to offset oxygen troughs

Light/darkness (hours)


Stocking density

Depending on the water system (replenishment rate): 1-5 adult fish/L; a low fish density leads to aggression

Tank dimensions

A key requirement for efficient gas exchange is a large water surface; a height of 25 cm is enough

Light intensity (lux)

54-324 lux at the water surface

Because fish are sensitive to vibration, make sure that the animals are housed or handled in areas that are free of vibration, away from equipment such as water pumps. Other than that, much remains unknown about the sensitivity of fish to laboratory noise. It is therefore wise to keep the level of unexpected noise in the laboratory down. It is also important to provide even lighting and not place tanks close to light sources that are (too) bright during the dark period of the LD cycle (“at night”). Lastly, white backgrounds and bright colors should be avoided; most of today’s fish facilities prefer and use grey and green tones. 

Since zebrafish are prey animals, sudden movements above or next to the tank will startle them. 

Zebrafish are extremely sensitive to heavy metals. Therefore, the input water and the water supply in the laboratory may not pass through copper or galvanized pipes and may not contact metal objects. The same goes for chlorine: it is important that chlorinated water is first passed through a filter.