I was waiting for a bus and had time to kill. That’s how it all began twenty years ago. I wandered into a pet store and became fascinated with the colorful fish on display. From then on, I was hooked by the aquarium hobby. I’ve kept freshwater tanks, marine tanks, brackish tanks, cichlid tanks and planted tanks since then. However, during twenty years I’ve never bred any fish. This always seemed like something that required too much time, space, or difficulty. I was almost ashamed to admit that after so long in the hobby, I’ve never seen a fish’s eggs or learned how to hatch brine shrimp.
Well, I finally managed to get the space and a few extra tanks in place last December. Participating in our aquarium club’s BAP program seemed like a good New Year’s resolution (and certainly more fun than the usual resolutions). All I had to do was pick a fish to start with. The following BAP report tells the rest.
BREEDERS AWARD PROGRAM (BAP) REPORT
Genus Name: Danio (danio = probably a native name)
Species Name: frankei (after someone named Frank)
Common Name: leopard danio
The danios are one of the most common aquarium fishes. These small fish are great for a community tank and are not fussy about either food or water conditions. All danios are schooling fish and because they are in constant motion, a school of them makes an impressive sight. In addition to being hardy, inexpensive, and easy to keep, they are also prolific egglayers. What could be a better choice for a first time breeding attempt?
The Leopard danio is a relatively new species of danio. It was originally described by Hermann Meinken in 1963 (ii). However, no type locality is known (iii) and this places the scientific naming process in jeopardy. Some authorities assert that this fish is a native of Thailand while others believe it a mutation bred from the common zebrafish or zebra danio (D. rerio) by someone in Czechoslovakia (v). Kerr (iii) describes D. frankei as a “somewhat mysterious variety whose taxonomic position is questioned” which “came to America from Germany by way of Russia”. Although several books list D. frankei as a distinct species (iv, v, vi) the origins and scientific classification of this fish remain unclear. Riehl and Baensch suggest that this fish be considered a morph of D. rerio, until proven otherwise, since D. frankei can be crossed with D. rerio.
Regardless of the scientific classification, the leopard danio is easily distinguished from the zebra danio by its color pattern. Leopard danios have a brassy gold coloration covered with a large number of small irregularly shaped, dark-blue or black spots. This is very different than the four horizontal stripes which identify the zebra danio. All danios possess two pairs of barbels. However, these are next to impossible to see because during the day they are held close to the face. Only at night are these barbels held away from the body, presumably to aid the fish in maneuvering. The maximum size for leopard danios is about 5cm to 6cm with the females being longer and much plumper than the males. In the aquarium, these fish swim actively and continuously just below the surface. A good aquarium cover is required to keep these fish from accidentally landing on the floor. Any food small enough to be ingested is readily accepted.
The leopard danios I acquired were a long-finned variety which were purchased approximately 15 months prior to my breeding them. These fish were kept in a 100-liter planted community tank with a variety of small barbs, loaches, and livebearers. The long graceful fins of these fish were easily nipped by other tank mates and show quality fish can’t be raised in a community tank. After this length of time, the fish were about 4 cm long and the females were easily distinguished from the males by the fullness and width of their bellies.
A 20-liter tank was cleaned and filled with aged tap water (pH 8.3, hardness 190 ppm CaCO3) to a depth of about 19 cm. A spawning grate was made by cutting a piece of plastic “egg-crate” lighting diffuser to the size of the tank’s bottom. The ½” square openings were further reduced by wrapping the egg-crate inside a plastic mesh (similar to an onion bag). The spawning trap is an essential piece of equipment because danios are avid egg-eaters. Determined danios will even try to struggle through the plastic mesh wrapped around the egg-crate and I’ve found fish stuck inside the mesh after spawning. Another commonly mentioned way of protecting the eggs is to use a layer of marbles. However, it takes a lot of marbles to cover the bottom of a 20-liter tank, and the plastic egg-crate is cheaper and easier to handle. A sponge filter, a couple of plastic plants, and a cover completed the spawning tank set-up. No heater was used and the tank temperature varied between 21C to 23C.
The danio’s habit of swimming near the surface makes them one of the easiest fish in the hobby to net. A single female and two males were easily scooped out of the community tank and placed directly into the breeding tank. No attempt was made to condition these fish by separating the sexes or feeding them a special diet. This transfer was made in the evening so the fish would have the night to settle down in their new tank before the expected morning spawning. However, the fish did not seem at all stressed by the transfer from the planted community tank into the almost bare breeding tank and within 15 minutes the males were pursuing the female.
Spawning in danios is an example of phototrophic behavior. This means that spawning is initiated by the morning light. For this reason, it is recommended that the breeding tank be located where it is exposed to a definite day/night cycle. Leaving the lights on constantly for 24 hours is not recommended for fish with this type of behavior. In my basement fish room a small window lets in natural light and all of the aquarium lights are on timers.
When spawning occurs, the male presses closely against the female and eggs and milt (sperm) are released simultaneously. The eggs are not adhesive and slowly fall to the bottom of the tank. However, the adults are eager egg-eaters and will rapidly devour any eggs they can find. My spawning must have occurred in the early morning because clear round eggs, of approximately one mm in diameter, were already present when I checked them the next morning. The adults were removed along with the spawning grate and plastic plants. It was difficult to count the number of eggs because they were hard to see.
Danio eggs are supposed to hatch within either 24 hours ( iii, viii) or two to three days (v). However, my eggs didn’t seem to be do anything except turn opaque. I thought I had lost the whole batch to fungus. However, the white opaqueness was just normal development and six days after spawning I noticed the first fry clinging to the sides of the tank. The long incubation time must have been due to the cooler temperature of the unheated tank.
The newly hatched fry were black and about four to five mm long. However, they were extremely slender and looked only slightly thicker than a hair. Feeding such small fry was a major concern. Several pieces of floating Cabomba from a community tank were added so the fry could feed on micro-organisms living near the surface of the leaves. An infusoria culture was also started by placing a few old lettuce leaves in a container of water. Although none of the organisms used as food were visible to the naked eye, examination under a microscope (50X magnification) easily revealed the presence of a variety of infusoria and nematodes. However, the number of organisms, even in the infusoria culture seemed small. A more abundant source of microscopic food was eventually obtained by growing a culture of Paramecium. The fry were feed an ounce of infusoria or paramecium three to four times per day, using a glass turkey baster, for the first three weeks. Then the fry were large enough to swallow live baby brine shrimp. The baby brine shrimp diet was continued until the fry were seven weeks old and could eat finely crushed flake food. By this time the fry had grown to between 1.2 cm and 2 cm in length. Their scales had a silvery sheen and the leopard-like spots were just becoming apparent. After eight weeks the fry were transferred from the 20-liter tank into an 80-liter tank. A total of 21 fish were present. All the fish exceeded 2.5 cm in length by the time they reached the age of three months. The fish are expected to be fully mature after 18 weeks.
Danios are supposed to be able to lay up to several hundred eggs. Although, the number of eggs couldn’t be counted, I doubt that there were more than three dozen laid by my fish. The small number of eggs might have been due to number of reasons. First, Ward (iv) states that D. frankei “is not very prolific, probably due to reduced fertility in the males” and claims that “it is still not an easy fish to breed”. A more likely explanation would be that the adults ate a large number of the eggs before they could fall to safety. Losses due to fungus and the lack of a good microscopic fry food during the first week or two may also have occurred.
Better results could probably be obtained by separating the males and females for a couple of weeks before breeding since I suspect that these fish spawn on an almost daily basis in the community tank. Fewer eggs would also be eaten if the water level in the breeding tank was greatly reduced. Zebra danios will spawn in as little as one to two inches of water (i, ii) and so leopard danios can probably be treated similarly.
Well, I finally did it! It really wasn’t that hard since several club members helped me out by answering my many questions (Thanks!). The excitement of seeing eggs for the first time and the even bigger thrill of seeing newly hatched fry makes me wonder why I waited so long. Also, I can now grow Paramecium, hatch brine shrimp, and have my first five points in the BAP program. I even made $10.00 selling ten leopard danio fry in our March auction. So, if there are any new (or old) hobbyists reading this who haven’t gotten around to trying breeding fish, I hope that you will give it a try. It was fun.
i) Axelrod, H.R. and Schultz, L.P., 1990, Handbook of Tropical Aquarium Fishes, T.F.H. Publications.
ii) Riel, R. and Baensch, H. A., 1994, Aquarium Atlas, vol. 1, 4th edition, Tetra Press.
iii) Kerr, F. J., March 1978, Aquarium News, 4-5
iv) Ward, B., 1989, The Aquarium Fish Survival Manual, New Burlington Books, Quill Publishing Ltd., London.
v) Van Ramshorst, J.D., ed., 1991, The Complete Aquarium Encyclopedia of Tropical Freshwater Fish, Bookmart Ltd., Leicester, UK.
vi) Cust, G. and Cox, G., Tropical Aquarium Fishes Freshwater and Marine, Lamplight Publishing.
vii) Meyer et. al., 1993, Proc. Roy. Soc. Lond. 252, 231-236.
viii) Andrews, C., 1986, A Fishkeepers Guide to Fish Breeding, Tetra Press.?