Breeding Danios and Devarios

There are many ways to breed the Danionins. Bearing in mind, that they are notorious for eating their own eggs the various methods used, all involve keeping fish and eggs apart.

It has long been said, that the easiest egglayer to breed, is the Zebra Danio: Danio rerio. In research institutions the world over, they are bred in vast quantities. One reason for this is that they are capable of producing at least three generations per year. So, if you happen to be studying genetics then the Zebra Danio will give results quite quickly. I know of one research facility that has in excess of 30,000 Zebra fish at any one time. That's a lot of fish in a lot of tanks!

So what is the best way to bred Danionins? The short answer is that there is not a best way just a way that happens to work when you try it.

The first item on the agenda is to find out the differences between male and female. Generally, the males are the most colourful and are slimmer. Females when they produce roe, start to become fatter. Having sexed them, what next? Well as a rule, I always separate males and females and condition them in separate tanks. Plenty of good live foods – Daphnia, Bloodworm or Mosquito larvae are all excellent foods. After about two weeks, the breeding process is ready to commence. Most Danionins will spawn at what we consider quite low temperatures. Anywhere between 18 and 24°C is fine. A small tank 18 x 10 x 10 inches is set up with part fresh and part ‘stock’ tank water . The next thing is to decide how to stop eggs and fish being in contact. Many people used a layer of marbles over the base of the tank. The eggs then fall into the spaces between the marbles and the fish are unable to eat them. I favour a different approach. The basket pictured below, is place on the 'side straps' of an 18 x 10 x 10 inch tank. The water level in the tank is adjusted so that the fish have about 1 to 1½ inches to swim in. This ensures that they are unable to eat the eggs. The fish are then placed in the basket – I like to use a ratio of two males to one female. This gives a better chance of the eggs being fertilised. It is possible to spawn one male and one female – it's just that bit more hit and miss!

Usually, they will spawn within 24 hours and you will see the base of the tank, covered in small clear eggs. If they do not spawn immediately, leave them for a further 24hours. If they still have not spawned, then return them to their separate tanks for further conditioning. If the species inhabits fast flowing waters, it is sometimes an advantage to have a couple of air stones in the breeding tank to simulate the flow in a stream. Having got the eggs, what next? First thing is to remove fish and spawning basket. I do not usually remove any infertile eggs. There are always far too many fertile ones that it makes little difference. The eggs should hatch within 24 to 36 hours. At that stage, they will still have their yolk sacs and will rely on that for food for the next 24 hours or so. During this stage, the fry attach themselves to the tank sides and cling there. When they have absorbed the yolk sac, they become free swimming and then require feeding. The best food I have found is ZM Systems 'Infusoria grade food'. This is a high protein food and is in a very finely ground state. A little of this, dispersed in water makes and excellent food for the first few days. At this stage, it is a good idea to add a small bio sponge filter and a few snails. The snails do a good job in clearing up uneaten food. As the baby fish grow, they are then introduced to newly hatched brine shrimp – Artemia nauplii. I feed brine shrimp once a day and dried food another twice. I now like to start doing daily water changes. About 20 to 25% is carefully siphoned off from the base of the tank. Check to make sure you have not caught any fry before throwing the water away. Replace with fresh water at a similar temperature. As the fry grow, they can be introduced to other foods, frozen Cyclops, chopped tubifex worms and live Daphnia etc. At approximately half an inch, they should be moved to larger quarters. The Danionins are very prolific and it is not unusual to have a spawning of several hundred fish from two or three females.

Other methods can be used to save the eggs when spawning occurs. Floating woollen mops are effective , as are mops placed on the floor of the tank. Plastic mesh – sold in garden centres is excellent. The easiest egg layer to breed? Possibly but beware those that decide they are not going to oblige so easily.