The Aquaria

For the fish to lay eggs they need to be kept happy and healthy – their overall well-being is therefore a top priority to us.

Our fish are housed in purpose-built aquaria. Water flows continuously to maintain oxygen levels and is filtered through a series of sand and biological filter systems and is treated with UV light to kill possible germs. Water quality is monitored daily. The systems are supported by full-time technical staff who run the facility and breeding programmes to the highest scientific and ethical standards.

Zebrafish are a shoaling species, therefore breeding fish are kept in social groups of about 20-40 individuals of both sexes.

They are fed twice daily on a mixture of dry flake food and live brine shrimp to keep them in peak health.

Eggs are obtained by natural matings, and are collected no more frequently than once a week.


The adult fish are kept on a fixed light/dark cycle (14 hours light, 10 hours dark). When the lights come on at 8 o'clock in the morning they get excited. The males chase the females and stimulate them to lay eggs. The males release sperm into the water as the females release their eggs; the eggs are fertilized in the water and then sink to the bottom of the tank.

Normally the adults will eat the eggs to recycle the nutrients lost in producing them. To prevent the eggs being eaten we put a mesh-covered container below the fish. The eggs fall between the holes and out of the adult fish's reach. Depending on what kind of experiment we are doing we can collect the fish in one of two ways:

Pairing – We might want to know the genetic make-up (the genotype) of two fish and so we put a single male and female into a small tank with a mesh bottom; When the lights come on the fish mate and the eggs of each pair can be collected separately. We can also use this method to interbreed two different fish lines.

Marbling – Alternatively if we want to have lots of eggs of one kind we can put a mesh bottom container in the fish’s normal tank. We put marbles over the mesh, as the fish seem to be stimulated by them!

The aquaria are inspected regularly by the Home Office. There are strict guidelines for the care and use of fish in research, which we adhere to tightly.

If you would like to know more about the ethics and regulations regarding animal research please visit the Understanding Animal Research website.