Oryzias woworae is probably the easiest ricefish species from Sulawesi to obtain in Europe. It is also the only species that has managed to become widely popular among aquarists and, at least in Germany, is now part of the standard offerings of almost every aquarium shop. However, in these days one often no longer finds the original form, but rather a much darker variant with more black or violet tones. In fact, one could say that the population of this species in the aquarium hobby is currently so secure that breeders specializing in ricefish no longer need to concern themselves with it. Nevertheless, I would like to write a few words about keeping and breeding this species, because it can be an excellent "beginner species" for some novices to gain their first experience with Sulawesi ricefish – precisely because it is so widespread and yet relatively easy to keep!
Like its two sister species, Oryzias asinua and Oryzias wolasi, which are considerably more difficult to breed, Oryzias woworae, being a very small species, is suitable even for aquariums with a side length of 60 centimeters. The aquarium setup can be customized to the keeper's taste, as long as the minimum requirements regarding temperature and water chemistry are met. Here, too, a certain degree of domestication is evident: the specimens available in pet stores today are significantly more adaptable than the first introduced animals, so there is practically nothing preventing successful breeding. I bred this species in pure tap water, which specifically means that the pH value was 7.5 and the water had a medium hardness of 10 °dGH. The temperature fluctuated between 22 and 25 °C; I did not measure any other water parameters.
The choice of food should be appropriate to the size of the fish: artemia nauplii, daphnia, fine flake food, and even small mosquito larvae are all suitable. The sexes are quite easy to distinguish: males appear significantly more colorful, while females are somewhat plumper and generally rounder.
The simplest way to breed Oryzias woworae is to place a spawning mop, similar to those used for breeding rainbowfish or killifish, into the aquarium. This artificial spawning substrate, consisting of synthetic wool with a float at the top, is usually readily accepted. The females transfer their eggs to the mop shortly after fertilization. After two weeks, the mop can be transferred to a small hatching tank, where the fry hatch after approximately two to three weeks, depending on the temperature. They are very easy to raise on fine dry food or on protozoa such as Spirostomum sp.
Older animals sometimes show distinct signs of aging. Some specimens become thin, while in others, the skin appears to become wrinkled. Still others develop an increasingly curved back. These changes are generally not pathological, and the animals can live with them for a very long time. Since such changes can also be observed in the closely related species O. asinua, they are probably not due to a lack of natural selection during the domestication process. Whether such signs of aging also occur in the wild is, to my knowledge, unknown. However, it must also be considered that very few specimens in the wild reach a comparable age to those in aquariums!
Gunnar Loibl
