Danios Fish
Among the most popular egglayers is the zebra danio (zebra fish) (Brachydanio rerio), a good example of the misleading character of popular names. Assuming that the zebra danio was named after the familiar four-legged animal, we would expect to see a fish with numerous vertical stripes, but such is not the case. The zebra has dark stripes running horizontally from the head and through the tail along the body, not at all like the striped "horse." It belongs to the Cyprinidae, the barb family.
The zebra has long been a pet of the aquarium, especially since it is so easily bred (with the help of a little imagination). Its breeding habits do present a problem, however, as you will see from the following description.
The zebra breeds at high speeds, scattering eggs as it travels the length of the aquarium and back in record time. The non-adhesive eggs fall as they may, wherever they happen to be dropped. In the average-size tank, at a water level of 8 inches, the zebras can make two round trips before the light eggs hit the bottom of the tank. Should the parents pass a few falling eggs on their return, they will quickly eat them as they go and then continue dropping, as though it were the most natural thing in the world. The aquarist must therefore find some system for the eggs to be trapped before the parents get a chance to catch them. Several methods have been devised, all being of equal value. One of the easiest to perform is as follows:
Place a long 20-gallon tank near a window; the sunlight will be beneficial for the propagation of algae and infusoria. Fill the tank with no more than 4 inches of water. Put in no sand or plants. Purchase some large marbles, the larger the better (those about an inch in diameter are about the best). Sterilize the marbles by boiling them in water for 20 minutes. After the marbles have cooled—do not cool them by dropping them in cold water as this will crack them—cover the entire bottom of the tank with them to a depth of about 1 inch. Let the tank stay in the direct sunlight for a few hours each day for three days. Then select the female that looks most promising and place her in the tank just prepared. It is easy to recognize the female by her full, rounded body in comparison with the slimness of the male. Also, you can determine the sex if you can spend time watching them by the fact that the males chase the females. You will see that the male fish show amorous attention to the females loaded with eggs and follow them very closely wherever they swim. If there is an empty female in the lot she will be noticed as a straggler. As soon as the female that you have placed in the new tank has become acquainted with her surroundings—it may take a day or two—place in with her three or four of the most active males, those that you have noticed have always been slim and fast. Do not choose a male straggler, as he will probably only eat the eggs instead of helping in their fertilization.
The reason for selecting three or four males is twofold. First, in case there should be any doubt, you want to be sure to have at least one male in the group; and second, assuming you are able to determine the sexes, it is best to have more than one male because if the female is well loaded she may drop more eggs than one male
can fertilize.
After spawning, the female will be slimmer than she was before, and all the fish should be removed to their previous home. The eggs will hatch in 56 hours at 75° F. At first the young will grow faster and stronger if fed entirely on live food, infusoria and then newly hatched brine shrimp. After three weeks to a month, depending on their size, they may be fed fine dry food alternately with microworms.
Since zebras get barely 2 inches long and the young grow rather slowly (an inch in six months), it is best to keep them away from the larger fish, especially the cichlids.
Newest of the Brachydanio species is Brachydanio frankei, the leopard danio, with a body that is speckled with tiny dots. They spawn just like the zebra danio and are just as hardy. There is still doubt with many as to whether or not these are hybrids, but Meinken in Germany has classified them as a valid species. Leopard danios will cross with other Brachydanio species.
All the danios may be bred alike. It may be interesting to note that this is the same way in which goldfish spawn.
