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 reproduction, and therefore to high metabolic costs. 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. In some parameters, peaks (nitrite, nitrate, ammonia) and drops (oxygen) may occur as a result of feeding and stressful events. For this reason, it is important to maintain safe margins and stay well away from the limits of the tolerated range. The monitoring frequencies mentioned in the table are indicative and depend on how stable the system is and how well it is managed.
| Parameter [monitoring frequency] | Values |
| Water temperature [continuous; daily] | 26–28.5 ºC; usually 28–28.5 ºC |
| 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 (0.02 mg/L);Nitrites: very strict: less than 0.1 ppm (0.1 mg/L);Nitrates: less than 50 ppm (<50 mg/L) |
| Dissolved oxygen [continuous; daily] | >6 ppm (6 mg/L); >7 mg/L is recommended to compensate for potential drops |
| Light/darkness (hours) | 14/10 |
| 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 vibrations, it is important to ensure that areas where animals are housed or handled are free from vibrations — for example, not located near water pumps. Other than that, much remains unknown about the sensitivitySensitivity Awareness of sensations. This includes the response to touch, pressure, varying temperature (heat, cold), light, and awareness of muscle tension (proprioception). Excessive stimulation of the nociceptors causes a sensation of pain. Chemicals can also cause sensory effects. of fish to laboratory noise. Therefore, it is advisable not to produce too many unexpected noises in the laboratory. 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 incoming water and the water supply in the laboratory should not pass through copper or galvanised pipes, nor come into contact with metal objects. The same applies to chlorine: it is important that chlorinated water is filtered first.
