An Introduction to Killifishes

The following article has been kindly provided by Richard Cox who is the editor of the British Killifish Association monthly journal. To learn more about the Association go to the club section at the top of the home page or alternatively click on the link at the end of this article which will take you to the BKA website.

This is an introduction to keeping killifishes aimed at the complete beginner. It will be phrased in simple language without the use of technical terms unless they are fully explained in the text.

It is not a definitive composition but purely the author’s own findings based on over thirty years of keeping these beautiful and somewhat challenging fishes. That is not to say they are difficult to keep and breed. Far from it but certain species are quite a challenge until the conditions required are mastered.

Firstly let us discuss what we mean by killifishes. They comprise a group of fishes of the family Cyprinodontidae and are commonly known as the egg laying tooth carps. They are found within the equatorial belts throughout the world and in practically all regions except Australasia. For the purposes of this article, in simple terms, they are divided into three distinct groups: the annuals, semi annuals and non-annuals. The annuals live in the wild for, usually, a single season in temporary ponds and swamp areas. With the onset of the annual rains they hatch from eggs deposited in the mud by the parent fishes. They then grow very quickly, maturing and breeding before the waters again dry. Semi-annuals live in areas which sometimes dry out but at other times retain water throughout the dry season. The non-annuals live in permanent bodies of water and, in some cases, will live for anything up to five years.

The types within the same groupings vary dramatically from continent to continent. The annuals of Africa, mainly a genus named Nothobranchius, vary in shape size and colour from the annual Cynolebias of South America. Such differences are to be found in other genera throughout the world. At the moment the classification of killies is undergoing many changes so I won’t dwell on this aspect in this article, as it will only tend to confuse. I can foresee, with the benefit of DNA testing, many more changes. To the beginner this is all very confusing but I can assure you that it is all very necessary. The naming of fishes is conducted in accordance with strict rules as laid down by an international body called the International Commission of Zoological Nomenclature. All scientists and taxonomists conform to the rules and decisions of the commission whose rulings are final and indisputable.

Thus you have order in this aspect of naming all creatures found on this planet of ours. Can you imagine the confusion if every other person discovering a new, or believed new, species went his or her own way? We, as hobbyists, are not bound by the rules or decisions and can call a fish by whatever name we choose but again, what a mess we would finish up in. There would be one fish being called several names by several people, fish being crossed and hybrids being produced. The point of this? Do be very careful to use the correct name for whatever species you handle and so do your bit to ensure that whilst in your hands the species stands a chance to survive pure.

Aquarium Requirements
In the wild a lot of these fishes are territorial by nature, the male defending his area against intrusion by other males. They mate with whichever females they can tempt into their territory but of course some species shoal and will not satisfactorily reproduce unless kept in similar conditions. In the main however, they can be kept in pairs or one male with two or three females. Accordingly they may be kept in relatively small tanks compared with other fish of a similar size. A tank measuring 12" x 8" x 8" will house a pair or trio of killies, in fact up to six of the smaller species can be kept in a tank of this size. Obviously a smaller tank can be used with very good results but from the beginner’s point of view it would be safer to use the larger tank thus lessening the risk of fouling and causing disease.

As a general guide species of up to two inches will be happy in a tank of the above size, species of up to four inches, in a tank size of 18" x 10" x 10" and the larger species such as Aphyosemion sjoestedti, should be housed in a tank of 24" x 12" x 12". Not everyone will agree with these sizes but if you want good size and good quality fishes (and who doesn’t?) the larger tanks usually produce larger specimens.

Most killies in the wild are found in shallow water so the depth of the tank is not important. A depth of six inches is adequate but a closely fitting lid and I do mean closely, is essential. Killies are excellent jumpers and if you leave a gap in the lid I promise you that they will find it and finish up on the floor! A lot has been talked and written about water conditions for killies. Yes, certainly there are those species that do demand certain conditions and they will not survive or breed unless they are made available to them. However, at this stage of our experience we would do well to avoid such fish as it would be neither fair to the fish or its keeper. You know experience is a great thing and it cannot be bought. It is something learned from life with time and practice, certainly keeping killifish is no exception. In the wild, for the most part, killies are found in soft, slightly acid water. However, experience has shown that they can be kept quite satisfactorily in whatever conditions are provided, within reasonable limits. The most important thing to remember is to acclimatise species to your conditions very gradually. I know only too well that there is always the desire to get a new fish into a tank as soon as possible but this could be the death of them. Not perhaps today or even tomorrow but they could die a few days later all because of a sudden change in water chemistry. This is something that should always be taken into consideration when making water changes with any fish in your care. Do it gradually and prolong its life and your enjoyment of the fish in question. Sudden changes of water conditions can cause gill injury or death due to shock, so please take care. Provided you follow this advice most killies will accept hard alkaline water but I don’t for one minute pretend that all will breed in such conditions. You may well find that you will have to soften and acidify hard alkaline water before some species will breed but again, some species such as the Epiplatys genus, will breed in almost any conditions. So in relation to water make up your mind what you are able to provide and stick to it. Don’t tackle the more difficult species until you have mastered the easier forms. Personally, I have always used aged rainwater to which peat has been added for a short time. A word of warning here, always boil peat before using it, thus removing a lot of the brown stain which leaches into the water in too great a quantity if not boiled. The water, when ready for use, should be tinged slightly brown. In order to prevent disease I also add a teaspoonful of cooking salt per gallon of water. I have always done this and have never suffered any major outbreak of disease

The question of tank decoration is a matter of individual choice. Killies can be kept in a bare tank with a nylon wool mop as an egg-spawning site. To make a mop take a book of between six to eight inches, wrap around about thirty turns of the nylon/wool, cut at the bottom edge, tie around the folded top and there you have it, a perfectly acceptable spawning mop. The colour? Well I would say stick to colours found in their natural environment, such as brown or greens, but I’m not convinced that it makes an awful lot of difference. If you wish the mop to float then tie a cork or similar object to it. I won’t tell you what to do to make it sink! However, you may prefer to keep your charges in planted tanks, in which case always be careful to select the right plants for the right conditions. Plants needing soft acidic conditions will soon die in alkaline conditions and vice versa.

For years I kept my fishes in bare tanks with either mops or Java moss as a spawning medium but have also kept them in planted tanks which I have come to prefer. I find that most killies breed perfectly well without my interference and will continually produce a stream of youngsters if well fed. They also display better colouring in a more natural environment. However, this is a matter of personal choice as already indicated.

When dealing with annuals and semi-annuals the requirements are somewhat different. In the case of annuals only one male per tank will be possible, as males tend to be very aggressive towards each other. They are better kept in a bare tank with just some cover for the females to hide in as males can be very aggressive towards the females and tend to continually ‘drive’ the females to spawn. As they are such hard drivers try to provide at least two females, if not more, to each male. However, do watch them closely for any signs of damage to the female and if so remove her for a rest. As a spawning medium I suggest boiled peat, although it does have the disadvantage of making the eggs difficult to find. Place the peat in a margarine tub, (or butter for those without a ticker problem!) cut a hole in the lid sufficiently large to enable the fish to enter thus helping to keep the peat in the tub. Silver sand can also be used. I’ve tried this but found that it does tend to foul quite quickly and I got the impression that some of the eggs were eaten, they being easier for the fish to find. However, I could be wrong.With semi-annuals either method will usually brings results. They will spawn in either mops or peat fibre or both. So, bare or planted tanks can be used provided that, in the case of planted tanks, the spawning medium can be removed to collect the eggs for ‘dry’ storage (of more later).

On the question of temperature, killies prefer a much lower range than the average tropicals. In fact if they are kept at too high a temperature they will soon let you know that they do not like it. Aim for a temperature of between 20º and 24ºC. (68º and 74ºF.). Only in a few species does it require a higher or lower temperature to be used.

In the wild killies eat mainly terrestrial insects, aquatic insects larvae and crustaceans. Accordingly, they do better on live foods but most will eat dry foods provided they are supplemented by live foods or high protein food such as minced beef heart. Favourites with killie keepers are Grindal worms, white worms and tubifex worms – although I personally do not recommend tubifex worms as I feel that they tend to foul small tanks quickly – wingless fruit flies, Daphnia, Cyclops and bloodworms. The latter are particularly good and are eaten with gusto by most killies. Good quality flake food can be given but do so sparingly. Remember you are usually feeding only a pair or trio of fish as opposed to the usual tank full! Many other foods can be used and are readily taken. In respect of other foods it is a question of suck it and see. If anything given is uneaten then do remove it to prevent fouling the water. This of course is applicable to all foods given; never leave uneaten food for any length of time.

Non annual species can be dealt with in two ways. Firstly they can be left well alone in a well planted tank and, provided cover is available for fry, they will usually come to no harm left with the parent fish. Secondly, the eggs are collected from the spawning mops and incubated in small containers. Most hatch between 10 and 30 days after spawning depending on the temperature at which they are kept. The lower the temperature the longer will be the hatching period and vice versa. On hatching very small fry will need infusoria as a first food. These are the small microscopic animals occurring naturally in water. A culture can be made using something like a bruised lettuce leaf in a jar of aquarium water. After a few days the tiny creatures will be seen with the aid of a hand magnifier and can be poured into the hatching container. Most fry will readily take newly hatch brine shrimp nauplii but do be careful with these as they soon die if uneaten and will very quickly foul the container and your fry will die. Most killie keepers use 500gm size margarine tubs as hatching containers so you can see that it will not take much to foul these. If too large a container is used the fry will find it difficult to locate their food and will thus starve and die. In most species growth is moderately slow but sure and a lot will live for three to five years. As they increase in size move them on to larger containers until by the time they are about half an inch long they can be transferred to an 18" tank. With semi-annuals I find the best method is to collect the eggs. Don’t worry about handling them as they can withstand considerable pressure. If they break when you pick them up then they were infertile anyway. Store the eggs on moist peat at the required temperature. By moist I mean more wet than that described for annuals. Add water to the peat until it can be seen just under the surface between the particles but not sopping wet if you understand. Just place the eggs on this so that you can watch their development with a hand magnifier. The fry inside the egg will usually let you now when they are ready to hatch. As a general rule when you can clearly see the fry’s eye, fully formed, it is ready to hatch. Return the eggs to water and they should hatch between four to ten hours. More often than not some will hatch within minutes of being returned to water. Others may not hatch and will require to be re-stored for a further period. Some of the semi-annual species can be very difficult to induce to hatch. Although the eye can be clearly seen and the fry look fully developed, the egg just sits in the water looking back at you! I remember a strain of Fundulopanchax amieti that positively refused to hatch no matter what I did. I never did solve the puzzle of what I had to do to breed this one! Feeding semi-annual fry is much the same as non annuals. Usually the fry are much larger and take brine shrimp nauplii and microworms followed quite quickly by Grindal worms as a first food. The fry grow quite quickly so the food requirements are that much more. Only experience will show you how much to give.

The eggs of most annual species have to be stored in ‘dry’ peat for anything from six weeks to nine months depending on the species involved. Now what do we mean by ‘dry’? Well by dry I mean damp. Aim for the same dampness as newly opened tobacco. Remove the peat from the spawning container using a very fine mesh net to hold it. Gently squeeze out all the surplus water. You will not harm the eggs; they can withstand tremendous pressure when you consider some are as small as a pinhead.

When all the surplus water has been removed place the peat and eggs into a plastic bag and mark it with the date and species name. Then store the bag for the appropriate period at a temperature of about 25º to 26ºC (77º to 79ºF.). A high shelf in a fish house or an airing cupboard will be suitable. On returning the eggs to water, having ascertained that they are ready to hatch by checking the eggs for the fry’s eyes, be sure to add salt to the water. A lot of annuals are prone to velvet disease and this will help to prevent it. This disease manifests itself as very fine peppery white specks on the side of the fish and with fry you just do not see it. Some very small annual fry will require infusoria but most will take brine shrimps immediately. They eat well and grow at a fantastic rate. With annual species you must pay very particular to the hatching container. It must be kept clean at all times and any uneaten food should be removed. It is also advisable to put a couple of small aquatic snails in the hatching container.

Just a word here about the phenomenon known as diapause. This is a natural device, which triggers or inhibits the growth of the embryo within the eggs of annual species. In any batch of eggs there will always be some ready to hatch whilst others have only developed to resting stages. So having returned the eggs to water, after you are satisfied that there are no more fry hatching, re-dry the peat and re-store for a further period, usually another month. Re-wetting can then be tried. I have known fry to hatch after each of four separate wettings. This is nature’s way of ensuring the survival of the species should the first rains fail and the pool dry after the fry have hatched. Thus, even though rains may fail completely for a season or two, viable eggs will still be in the mud at the bottom of the pond.

There is nothing mysterious about killifish, they are no more difficult to keep and breed than any other tropical species. The average aquatic dealer cannot obtain stocks and when they do the price is usually high. However, within the British Killifish Association there are usually a hundred plus species available and details of how to find us are within this web site.

Well there you have it. I have tried to give a full as possible general introduction to killie keeping. I sincerely hope that some of you will venture into the world of killies and enjoy this aspect of fish keeping.

British Killifish Association

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