by David Schaeffer
If you’ve ever wanted to keep any of the mind-blowingly colorful killifish seen in aquarium books, you were probably put off by phrases like “delicate and fussy,” “short lifespan,” “requires soft, acid water” and “requires live foods.” While those things may be true for certain killies, blanket statements like these conceal the fact that a whole host of killies live for several years, will eat anything as long as it’s food, and will live in almost any water as long as it’s wet.
“Why don’t I see them for sale at pet shops?” you might ask. There are several reasons. In most cases, they are not prolific breeders on the scale of most commercially viable egglayers. They also tend to be “continuous breeders,” dropping a small number of eggs daily during their entire adult life. This obviously precludes raising the fry in large batches, the way you could do, say, with zebra danios. The killies that can produce hundreds of eggs in a given week tend be what are termed “annuals,” with eggs that can take many months (!) to hatch. The cost of raising them in commercial numbers would make them quite pricey by the time they reached the pet shop, and they are generally not found in large enough groups to make collecting commercially viable. Luckily, there is a large number of obsessed, er, I mean dedicated, hobbyists who breed these guys and are usually more than happy to help you get started.
A “killifish” can be defined as a fish of the order Cyprinodontiformes that lays eggs. There is at least one killie to fit every budget, tank size, and set of water conditions. They get their name from the old Dutch word “kill,” meaning “creek,” and many of them, especially the more colorful and desirable species, are to be found in small jungle creeks in Africa, Asia, and South America. However, the group as a whole is found on every continent with the exceptions of Australia and Antarctica. Their live-bearing cousins, the platies, mollies, guppies, swordtails, etc., are familiar to all aquarists and reflect the diversity that can be found in this order. Cyprinodontiform fish (in Latin, that means “toothed minnow-like,” for you trivia buffs out there) can be found in blackwater streams with a low pH and no measurable hardness, in brackish water, in pure seawater, in hot springs with a salinity well above that of the ocean, and even temporary water-holes that are dry for many months of the year. The group as a whole is extraordinarily adaptable, though each species will have its preferences.
Rivulus xiphidius
One of the best-kept secrets of killie-keeping is that while most other egglayers require some “tweaking” to get into spawning condition, most killies, if kept properly, are virtually guaranteed to spawn. If they’re in good health, you’ll find eggs sooner or later. For this reason, I recommend the easier killifish as a great introduction to breeding egglaying fish. In addition, the eggs are often rather large and develop slowly, allowing you to observe the development of the fish embryo. Talk about educational! Even better, the eggs are DURABLE. You’ll often see references in books to picking the eggs from spawning mops: it means exactly what it says. The eggs are tough enough to be picked up by human fingers without suffering harm. Their size and durability makes them easy to incubate separately from the adults, if you so desire.
Depending on the type of killifish, eggs can take from about two weeks to a staggering nine months or more to hatch (!) for some varieties. This is another one of the features that makes it unlikely that they will ever be a big commercial success, but it gives the aquarist plenty of time to prepare properly for the arrival of fry.
Their life in the tank can range from a year or so for some annuals to several years in the case of many non-annuals. As if to make up for the brief time they spend alive, however, annuals mature early (often being capable of breeding one month after hatching!) and nearly all are adorned with some of the most spectacular colors to be seen on a freshwater fish.
In terms of feeding, most varieties will adapt to flake or pelleted foods, but some trial and error may be in order. Frozen foods and live foods will enhance color and egg production.
Another one of the features that make killies great aquarium residents is that while most of the colorful forms come from tropical and subtropical areas, many of these still appreciate cooler temperatures. The jungle steams or savannah ponds where these species live are kept cool by evaporation, and this translates into fishes that do fine at room temperatures. I’ve found in my own tanks that Fundulopanchax gardneri, a colorful and hardy killie from western Africa, displays brighter colors and lives longer when kept in the upper 60’s °F. The only side effect of temps around 68°F. was lower egg production. Many species are also tolerant of water conditions very different from their native habitat. While the most colorful forms often come from soft, acidic water, a good percentage of these will do well, and even breed, in hard, alkaline water.
Fundulopanchax gardneri N'sukka
Killifish, as a general rule, do best in a species tank, without any roommates, although, again, each species will be a bit different. One generalization that I can make is that, as with almost any fish, good water quality is a must, especially when raising youngsters. Good biological filtration and frequent partial water changes are called for, but the payoff will be worth it.
The key, as with any other fish, is to research the individual requirements beforehand in a reliable reference source. Contact the American Killifish Association, one of your local aquarium clubs, or, as always, a good book.
Next time, I’ll be discussing one of the great beginner killies, Fundulopanchax gardneri, a stream and swamp dweller from western Africa.