To safeguard your next generation of fish, you need to be especially attentive during the hatching of the eggs and for the critical first few days after the fry emerge. The hatching period depends not only on the species, but also on the water temperature. In most cases, the fry hatch within a couple of days, although there are exceptions, such as with annual killifish.
At first, you may not even notice the first fry to hatch, because they are not free-swimming immediately. Instead, they rest on the floor of the breeding tank or among the plants, using up the remains of their yolk sacs from the eggs. This sac, which you can see on the underside of the body, provides the fry with nutrients.
Feeding fry
Once the young fish start to become free-swimming, they need to find food for themselves. You can supply them with various types of proprietary foods to help meet their nutritional requirements at this stage. Choose a food specifically intended for the type of fish you are rearing, to ensure that the particles are of an appropriate size to suit the fry. Livebearers’ offspring are generally quite large compared with the fry of egg-layers, so can generally eat larger pieces of food. Anabantoids are among the smallest fry and they must be given food small enough for them to cope with or they will starve in the critical early days after they become free-swimming. In some cases, however, the actual body size of the fry does not correlate closely to the size of the mouth.
Growing food
If obtaining commercial fry foods is difficult, or as a supplementary source of food, you can grow your own cultures very easily. You should set these up in advance of the anticipated spawning in order to be prepared. The first food fry consume are known as infusoria -tiny microbes that develop in a jar of water. Include some vegetable matter in the jar, preferably organically grown, to avoid the risk of chemical contamination. The protozoa and other microbes forming the infusoria do not survive well in heated water, so must be cultured outside the tank then added subsequently. Making an infusoria culture
- Leave a jar of ordinary tap water without a lid for a day, then add a lettuce leaf or a small amount of straw.
- Place it in bright light, on a window sill for example. The water will turn cloudy within a few days, indicating that the microbes are developing.
- To feed the fry, suck up some of the water and place it close to the fish in their aquarium. Young fish cannot swim far, so direct their food within easy reach at first.
- Feed them small amounts on a regular basis. Set this up on a drip flow if you have to be out for long periods.
Brine shrimp
For feeding larger fry, small crustaceans called brine shrimp (Artemia salina) are often used. These are available as eggs, which you combine with salt water according to the accompanying instructions, in order to make them hatch for a fresh supply of fry food.
The hatching rate may vary, and it will improve your yield if you aerate the water initially; this should help the eggs’ thick outer casing to become saturated, which is essential if they are to hatch. At a temperature of about 25°C (77°F), hatching should occur within a day or two. Set up several cultures, each spaced two or three days apart, to ensure you will have a constant supply.
The young that hatch, called nauplii, are the larval form in the life cycle of the brine shrimp. You need to establish enough cultures to provide food for roughly seven to 10 days, after which the fish can be transferred onto powdered flake or similar foods.
You can carefully siphon out the brine shrimp which have hatched as they will be in the main body of the water, whereas the indigestible shells and unhatched eggs will remain on the bottom. Sieve the nauplii and dunk them in dechlorinated fresh water, to remove the inevitable salty residue, before offering them to the fish.
Other rearing foods
Another food that is valuable for rearing purposes are microworms. These are cultured in a similar way to whiteworm, with cultures being set up sequentially. It takes 10-14 days for a culture to provide a harvestable quantity of microworms.
In an emergency, you can use finely sieved egg yolk as an alternative. Push the yolk through muslin to produce miniscule particles suitable for the fry. Only use this food with caution, however, because too much will pollute the water.
Housing the fry
Before long, presuming that you have successfully reared a large number of fry, you will need to split them up and transfer them into other tanks. If they become overcrowded, this will stunt their growth and lead to a rapid build-up of pollutants in the tank which will make them more vulnerable to illness.
It is advisable to separate the fish into batches partly based on their size, otherwise fast-growing individuals of cannibalistic species such as piranhas (Serrasalmus species) will start to feed on their smaller fellows. Some losses will be inevitable, however, even with the best care. You should also weed out any obviously deformed individuals – with badly formed tails, for example -and destroy these humanely. In the wild, these would inevitably fall victim to predators.
With species that do provide parental care for their offspring, it obviously adds greatly to the interest of breeding them if you can observe this behaviour at close quarters. As well as the breeding tank, remember that you will also need to set up alternative accommodation for when the time comes for you to separate the adult fish from their brood.
