THE AKA BEGINNERS GUIDE
This guide is intended to provide basic information for newcomers to keeping killifish. The information provided here was derived largely from the AKA's Beginners Guide, by Alan C. Markis and Roger W. Langton. The latest edition of this booklet, edited by Edd Kray, is more complete than this online version and contains more photos. It is offered to all new members of the AKA for a nominal charge, or it is available thru our comprehensive on-line store. Click on Join AKA at the top of the page to access an online application.
Table of Contents
Selecting Killifishes
Fundulopanchax SA Annuals Epiplatys Nothobranchius Hybrids Quality
Plants and Aquascaping Lighting Aeration and Filtration Temperature
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Feeding Killifish
Brine Shrimp Daphnia Mosquito Larvae Tubifex Worms Black Worms White Worms Fruit Flies Beef Heart Paste Foods Dry Foods
Microworms Vinegar Eels Infusoria Grindal Worms |
Breeding Killifish Plant Spawners
Harvesting Eggs, Incubation and Fry The Water Incubation Method The Vaporizing Method The Permanent Set-Up Method The Peat Moss Method
Harvesting Eggs, Incubation and Fry |
Selecting Killifishes
Pet shops, with some exceptions, do not carry many killifishes. They may occasionally have Aphyosemion australe, Fundulopanchax gardneri, or Fundulopanchax sjoestedti (Blue Gularis) and once in a while other species may be found. The best source of killies is the Fish and Egg Listing (F&EL) found in the Business Newsletter of the AKA. The BNL is sent to all members of the AKA each month. For more unusual or rare species, the New and Rare Species Committee of the AKA is a good source. Finally, if you become acquainted with other killie enthusiasts, or if you can join a local killie group (see the Affiliate Clubs link at the top of the page), this is an excellent source of both fish and advice. It can be difficult for beginners to know exactly what fish to purchase because killifish are generally referred to (especially amongst enthusiasts) by their scientific names and some familiarity is needed to know what fish these names represent. As you read about the various species in publications like the Journal of the American Killifish Association (JAKA) and a variety of books that are available, you will develop a sense for the fish. When the time comes to choose your first killies, do so with care. Needless to say, choose healthy fish, but be careful also to choose fish that are correctly identified. Many species and strains of killifish look very similar and killies sold in pet stores are frequently misidentified. Furthermore, many killifish are maintained as known locality strains. For example Nothobranchius rachovii Beira '91, a very beautiful fish, represents a particular strain of this species identified by the locality and the year in which it was collected. It is strongly felt, in the killie hobby, that such strains not be crossed with others, even when they appear to be the same fish. Such crossings can produce hybrids, which may be sterile, or at least are fish that nature never produced. The remainder of this section will briefly discuss some of the genera of killifish, and some of the species found within them, with a particular emphasis on those that are suitable for beginners.Aphyosemion
This is one of the most popular of the killifish genera among hobbyists, and it contains a large number of species that are maintained in the hobby. These species hail from west Africa, many are beautiful and relatively easy to maintain and breed. Most are spawned on floating mops (see below). One of the most commonly seen and a suitable beginner's fish, is Aphyosemion australe, one the few killies that does have a common name, the Lyretail. This species spawns in floating mops. It comes in three color strains. The Chocolate is the natural form, while the Gold and the Orange were developed in aquarium populations. Other species in this genus that are suitable for beginners are A. calliurum, A. ahli, and A. bivittatum. Aphyosemions with the same species name are often identified as coming from specific populations or locations. Different populations may or may not be genetically identical.Fundulopanchax
This genus contains several very colorful species that are suitable for beginners. These include the popular Fp. gardneri, Fp. filamentosus, and the emblem fish of the AKA, Fp. sjoestedti. Many of the strains of Fp. gardneri are relatively easy to maintain and breed as is Fp. filamentosus. Fp. sjoestedti is a little more challenging, although it can be hard to resist its charms. All of these species come in several strains. Some Fp. gardneri are top spawners, while Fp. gardneri nigerianus and Fp. gardneri garderni are switch (top/bottom) spawners. The other two species mentioned are bottom spawners.South American Annuals
There a several popular genera and species amongst the South American annuals. Nematolebias whitei is an excellent beginner's fish, easily bred and cared for in the aquarium. It is a truly elegant fish and its spawning behavior is fascinating. Perhaps its only disadvantage is that, like many other annuals, the beginner has to wait for some months between first spawning and first hatch.Epiplatys
Species in this genus are surface fish, feeding on insects that fall into the water. They prefer to lay their eggs at the top of floating mops or plants. They are hardy, many are of good size, and many are easily bred and maintained in aquaria. Good examples, and good choices for beginners are E. sexfasciatus and E. fasciolatus. The genus also contains some challenging species. For example, the diminutive E. annulatus, although strikingly beautiful, would not be a good beginner's choice.Nothobranchius
These East African annuals are among the most beautiful tropical fresh water fish in the world. N. rachovii is often referred to as the most beautiful fresh water species in the world, and deservedly so. Colors are brilliant in almost all species within this genus. Among these species, N. guentheri and N. korthausae are excellent beginner's fish. If you decide to try these fish, you should be aware that they are susceptible to the protozoal disease, velvet, and they should be maintained in water containing 1/2 to 1 teaspoonful of salt per gallon. Otherwise they do well in a variety of water conditions, including somewhat hard, alkaline water. Again, breeding them requires patience as the eggs require a prolonged dry period, although N. korthausae is among those with relatively short dry periods. There are many other interesting genera, including the North American native killies, including the Desert Pupfish and the Florida Flagfish, Jordenella floridae, the genera Rivulus, Rachovia, Austrofundulus, and on and on. Many of these are discussed elsewhere on this site.Hybrids
As discussed already, it is easy to hybridize some of the killies species. It is the policy of the American Killifish Association to discourage hybridization except for scientific and research purposes. The organization believes that the fishes should remain as they are in nature and that hobbyists should not intentionally change color patterns, form, or identity. Every member of the AKA is urged to maintain this policy.Quality
Everyone is urged to maintain the highest standards in his fish keeping by maintaining optimum environmental standards for his or her fish and by only passing on fish to other hobbyists that meet the highest standards of good health and color. Good luck with your hobby and may you have many years of success and enjoyment with killies. If you are not yet a member of the AKA, we look forward to having you join and meeting you.General Maintenance
Housing
In general, killies are kept in small aquaria, often as small as 2.5 gallons. For breeding, in particular, small tanks are preferred. Besides allowing closer observation of the fish, small tanks allow the aquarist to separate pairs and trios of different species. Most killie enthusiasts soon acquire several species, and we may as well mention here that, for the purposes of breeding, it is essential that different species, and even different strains, be kept strictly separate. Closely related species can breed and produce hybrids, but serious killie keepers strive to maintain different species in the "pure" state. Furthermore, hybrids may be infertile. Obviously, tank size must match fish size and larger fish, like Fundulopanchax sjoestedti (the Blue Gularis) require 5 or 10 gallon tanks. Larger aquaria, for example 10 or 15 gallon, or even larger, are used also for raising young fish.
As will be discussed later in this document, fry are often hatched in smaller containers, such as plastic "shoe boxes" or other storage boxes. In a typical fishroom for killifish, therefore, you will usually see tanks and containers in a wide variety of sizes. How these are arranged is a matter of personal taste, but killie fishrooms often have racks of tanks with small breeding tanks on top and larger rearing tanks below. One advantage of a fishroom is that the whole room, rather than individual tanks, can be heated. The fishroom shown here is that of Norbert Dadaniak in Germany. You can click on the image to see it at larger size. Use the Back button to return to this page.
Plants and Aquascaping
Planted tanks are pleasing to view, and plants help to utilize organic wastes produced by the fish and, to some degree, in oxygenating the water. However, many killie keepers avoid the use of plants in breeding tanks, and even in rearing tanks. Plants can make the collection of eggs, described later, difficult. Furthermore, bottom spawners may spawn in the gravel substrate, which is may be undesirable. On the other hand, one technique for spawning the "plant spawners" involves the use of a permanently planted tank and some breeders spawn bottom spawners over gravel. A common compromise is to use bare breeding tanks, and planted rearing tanks. What plants to use is a matter of choice for the aquarist but, because killies often do best in tanks with relatively low lighting levels, plants tolerant of low light conditions are best. These include the cryptocorynes, Java moss, and Java fern. If gravel is used as a substrate it usually should be of a type that will not harden the water. A quartz sand or fine gravel favored by aquatic plant enthusiasts is #3 blasting sand, available at many hardware stores.Lighting
Many killies, such as the Aphyosemions, come from forest streams that are protected from direct sunlight, and prefer subdued lighting. In brightly lit aquaria, plants may provide some shading for killies that prefer low light conditions. Many killies appear at their best when light falls from above and to the front of the tank. Because of this, many killie enthusiasts illuminate their tanks, especially breeding tanks, by ceiling lights, with fixtures over only those tanks where more intense lighting is required.Aeration and Filtration
Small aquaria, such as are often used for housing killies, are more easily polluted than large aquaria. The relatively small volume of water easily accumulates waste products, generating ammonia and nitrites, which are extremely toxic to fish. Most killie keepers, at least in the United States, therefore utilize some form of aeration and filtration. Air driven filters provide a home for aerobic nitrifying bacteria, which break down the harmful ammonia and nitrite to nitrate, a much less toxic end product. Various types of filters can be used, but for small tanks the most popular are simple box filters, containing filter "wool", or sponge filters. Both provide a large surface area for bacteria to colonize and filter particulate matter from the water. Sponge filters have the advantage of not entrapping fry, a potential problem with box filters. In larger aquaria where a substrate is being used, under-gravel filters may also be used.Temperature
Ideal water temperatures vary depending on the species, but for most killifish the temperature should be in the range of 72-75 °F. Conventional aquarium heaters may be used, but because serious killie keepers have several or many tanks, it is common for the whole room to be heated. Another advantage of this approach is that tank covers do not have to accommodate heater cables. Many killies are great jumpers and will exit the tank, and this life, through such small openings. The killie fancier, therefore, must ensure that tank covers are closely fitted.Water Conditions
It is impossible to generalize about the water conditions required by killies. Some, such as A. cameronense come from soft, acid waters, while others come from harder, alkaline waters, and others from brackish waters. Some killies must have particular water conditions. Others, such as Nothobranchius species, can tolerate a range of water conditions. Naturally, no fish should be subjected to sudden changes in pH and hardness.pH
The pH of water, or a solution, is a measure of the concentration of hydrogen ions (H+) expressed on a negative logarithmic scale. Pure water is neutral, having a pH of 7.0. Acidic water has a pH less than 7.0 due to an increased hydrogen ion concentration, while alkaline water has a pH greater than 7.0. In both cases the change in pH is due to dissolved substances in the water. It is useful to have some means of testing the pH of the aquarium water. This may be done with test kits using indicator solutions, with pH papers, or most conveniently with an electronic pH meter. Small hand-held, battery powered pH meters are now available for relatively modest cost. Fish should never be exposed to sudden changes in pH. Thus, fish being newly introduced are usually acclimated by slowly mixing the water of the new environment with the "old" water. The pH of water may be changed using weak acids, such as sodium biphosphate (NaH2PO4) or weak bases, such as sodium bicarbonate (NaHCO3, or baking soda). It is easy to change pH excessively using these chemicals, and the pH change produced may not be stable. A better way to reduce pH is to filter the water through peat moss. The peat moss is best boiled and rinsed then placed in a box filter between layers of filter wool. After a day or two the water will be amber and somewhat more acid. To increase pH it is best to include some form of calcium carbonate in the tank, such as a lime sand or gravel. Carbon dioxide (CO2) released as a waste product by the fish dissolves in water to produce carbonic acid, which will react with calcium carbonate to produce soluble calcium bicarbonate. The latter provides buffering capacity, helping to stabilize the pH of the water in the aquarium.Water Hardness
Water hardness refers to the amount of calcium and magnesium salts, chiefly chlorides and sulfates, in solution. Hardness is measured in Degrees of Hardness (dGH) or as parts per million (ppm). It is common to see two types of hardness discussed, permanent hardness (calcium and magnesium salts other than bicarbonate) and temporary, or "carbonate" hardness (calcium and magnesium bicarbonate). The latter is a measure of the buffering capacity of the water, as previously discussed. Hardness can be measured using titration methods, and kits are available to measure both of these forms of hardness. However, for most purposes the conductivity of the water, as measure of total dissolved salts, is adequate. Small battery powered conductivity meters, which measure total dissolved salts in ppm, are available for this purpose. In most cases, the hardness of water is not as critical as pH. Water of 120-160 ppm is satisfactory for most killies, although there are some species that do best in very soft water, and some that do best in hard water. Water that is considered too hard can be diluted with rain water or artificially purified water. The latter can be produced using ion exchange resins or RO units. Ion exchange resins exchange sodium ions for calcium and magnesium. RO units remove calcium and magnesium ions through a process of filtration. Good RO water, therefore, is similar to distilled water. In recent years small, reasonably priced RO units have become available for use in the aquarium hobby and are seen in many fishrooms. Fish moved from hard water to soft should always be slowly acclimatized.Feeding Killifish
A varied and balanced diet is a practical necessity to achieve any degree of success with killifish, particularly in breeding them. Many killifish do really well only if supplied with livefood. Others do well on frozen foods and some, on dry foods. At any rate, exclusive use of a single food should be avoided, as this practice is likely to lead to nutritional imbalances and deficiencies. You will find useful information on foods on other sites, such as the Krib.Feeding Adult Killifish
Brine Shrimp
This food is a staple of many killie fishrooms. In some areas live adult brine shrimp can be purchased. These are a good nutritional source and are eagerly taken by most killies. As they live in strong salt water, they are less likely to carry parasites and bacteria harmful to freshwater fish. Frozen brine shrimp are widely available and widely used. They are readily accepted by most fish but, as with any non-live food, care must be taken not to overfeed.Daphnia
This little crustacean is one of the most widely used live foods. Daphnia can be cultured artificially, at least in limited quantities, but most aquarists collect them from pools and ponds. A drawback to use of daphnia collected in this way is the danger of collecting other organisms potentially dangerous to aquarium fish. Daphnia are said to act as a laxative for fish and, like other foods, daphnia should not be fed exclusively.Mosquito Larvae
This is an excellent live food for killies, although available only seasonally. They may be collected from standing water and ponds, either by swiftly passing a net through the water near the surface, or by collecting the egg "rafts", which can be allowed to hatch in a container of water in the fishroom. Many aquarists recommend culture of mosquito larvae by leaving out a container of water, which is allowed to become green with algae. The egg rafts or larvae are then collected under controlled conditions. Care must be taken to avoid allowing the larvae to complete the life cycle and become mosquitoes. That is a good way to make yourself unpopular with the neighbors and should be avoided because of the mosquito borne West Nile virus. As with the collection of other live foods, there is a risk of introducing fish enemies with the food.Tubifex Worms
Tubifex worms are small worms that live in filthy places, such as sewage run-offs and the like. They can be collected from such sites, or purchased from some stores. Tubifex are an excellent food for killifish, but they carry the reputation of transmitting a variety of diseases. This risk may be reduced somewhat by holding the worms for a time in a shallow tray through which cold water runs. In this way evacuated matter and detritus from dead worms are washed away.Blackworms
Blackworms are similar to, but distinct from, tubifex worms and are also an excellent food. They can be purchased, either from a store, or directly from companies that grow them for profit. Some of these producers are associated with fish farming operations. Others are dedicated purely to growing blackworms. Those associated with fish farms may be more likely to transmit fish diseases. Like Tubifex, blackworms carry a reputation for transmitting diseases. However, some breeders swear by them. Blackworms may be maintained for some time under running, cold water or refrigerated in dishes with enough water to barely cover them.White Worms
White worms (Enchytrae) are another excellent live food for killies. Possibly they too can carry parasites or pathogenic bacteria but, because they are cultured, this is less likely than it is for tubifex and blackworms. It is said that white worms are fatty, and that they should not be fed exclusively for that reason. There are many methods for culturing white worms. Starter cultures can be obtained from other hobbyists and they are often listed in the Fish and Egg Listing of the AKA's Business Newsletter. Typically, these worms are cultured in a mixture of potting soil and peat moss, usually about 50:50. However, some hobbyists use garden soil, leaf mold, etc. It is best to sterilize the substrate before starting the culture. One way to do this is to place the mixture in a plastic bag and heat it in a microwave for a few minutes. After cooling the substrate is placed in a box, allowed to cool, sprinkled with water until thoroughly damp, and the starter added. The worms may be fed baby cereal or boiled oatmeal, but the most commonly used food is break soaked in milk or in yeast water (a milky suspension of yeast in water). These worms do not like high temperatures, the ideal being about 50 °F. Worms may be collected by picking them out, if the culture is a good one, or by placing some of the substrate in a strainer over a container of water. A light bulb is positioned over the strainer, which drives the worms through the strainer and into the water. The worms can be washed, then fed to your killies.Fruit Flies
Two fruit fly (Drosophila) mutants, vestigial wing and flightless, make excellent food for killies. By virtue of the mutations they bear, they cannot fly. They can crawl, though, so it is advisable to feed just enough that the fish will eat them immediately. These flies are usually cultured in some sort of bottle into which a fruit fly medium, with a sprinkle of dry yeast, has been placed. The bottle is plugged with a piece of plastic sponge, or some such thing, after the flies are added. After some days larvae will appear, which then pupate, and eventually adult flies will emerge, at which stage they can be fed to the fish. Fruit fly medium can be cooked, but this is a time consuming and messy business. Instant medium can be obtained from biological suppliers such as Carolina Biological, and is much easier to use. A starter culture of flies can be purchased from similar sources, or obtained from other hobbyists. Starter cultures, again, are often listed in the F&EL.Beef Heart and Paste Foods
Beef heart, trimmed of fibrous tissue and fat, can be frozen, then grated to produce "worm-like" pieces. Many hobbyists use beef heart as the basis for a prepared food containing vegetable matter, vitamins and other additives. Others prepare similar paste foods based on shrimp and fish. These are fed as small pieces or gratings. Care must be taken to feed only as much as will be eaten immediately, as remnants of this type of food can quickly foul the water. Here is a recipe for a (non-beef heart based) paste food. Recipes can also be found on the Krib.Dry Foods
Many quality dry foods are available in the hobby today. Killies have a reputation of being reluctant to eat dry foods. However, some will eat them readily, and others can be trained to do so. The advantage of commercial dry foods is that they contain a balance of nutrients, including vitamins.Foods for Newly-Hatched Killifish Fry
Newly-Hatched Brine Shrimp
Virtually every breeder of killifish uses newly hatched brine shrimp (nauplii of Artemia) as a food for fry. Many killie fry can eat them as a first food, and even small fry can eat them after a few days on infusoria. Artemia eggs are available commercially, from aquarium stores and other suppliers. Essentially, the aquarist hatches these eggs by incubating them in a salt solution (6-8 tablespoonfuls per gallon). A number of methods have been described. One method is to hatch the eggs in a tray, using a light to attract the newly hatched shrimp. Others hatch the fry in jars, aerating the salt solution. A popular variation today is to use inverted clear plastic soda bottles (2 liter), from which the bottom has been cut. A piece of tubing is glued into a hole drilled in the cap and used to aerate the solution. The inverted bottle can be held in some sort of frame, often one holding two bottles. A useful advance in hatching brine shrimp, especially those of lower grade, is dechorionation, in which the "shells" of the eggs are removed before hatching. Again, methods vary, but the one described here is used by a number of aquarists. A cup of cool water is placed in an inverted soda bottle hatchery (as described above) and one teaspoonful of brine shrimp eggs is added. This is allowed to bubble gently for about an hour. One cup of concentrated bleach (such as Chlorox) is added and the solution bubbled vigorously for 6 minutes. During this time the suspension of eggs will turn from brown to orange. The suspension of eggs is then run off the hatchery and strained through an ordinary white handkerchief. The eggs are rinsed thoroughly with cool water, then returned to the hatchery, in which the salt solution for hatching has been placed. This suspension is bubbled at a moderate rate. The eggs will hatch after 24-36 hours, depending on temperature. Temperatures of 72 to 80 °F are suitable. The hatched shrimp are collected by straining through a handkerchief. The advantage of this method is that very high hatch rates are almost always achieved, even with brine shrimp eggs that give only modest hatches without dechorionation.Microworms
Microworms are another excellent first food for killifish fry. Starter cultures are often listed in the F&EL. To culture them, baby cereal is added to a suitable plastic container (say a one pint translucent container of the type often used to sell food). Water is added to make a paste. A little dry yeast is sprinkled onto the paste and the starter added. After some days microworms can be seen crawling up the sides of the container. They can be scraped off with a finger or a small stick and fed directly to the fry. After some time the culture will begin to sour, at which time a new one should be started.Vinegar Eels
These tiny worms are also an excellent starting food for fry. They have the advantage of staying suspended in the water, where they can live indefinitely. They are easy to culture, but more difficult to collect that microworms. To culture a large jar, such as a one gallon pickle jar, is almost filled with a 50:50 mixture of cider vinegar and water. A small piece of apple is added, and the stared culture added. After some days thousands of tiny worms can be seen suspended in the vinegar. These cultures will go on for many months with little or no attention. To feed, the worms must be strained through a fine material such as filter paper and rinsed several times to remove the vinegar, which would otherwise acidify the hatch water.Infusoria
Infusoria is the collective name given to a host of tiny organisms that live in naturally conditioned water. Green water, for example, contains such creatures. For feeding newly hatched fry that are too tiny to take the foods described above, green water may be cultured, or cultures of paramecium may be maintained. Paramecium starter cultures may be obtained from biological suppliers, or again through the F&EL. To maintain a culture, a large jar, such as a one gallon pickle jar, is nearly filled with chlorine free water (tap water allowed to stand to remove chlorine), and a few dry peas and a sprinkle of baby cereal added. After a couple of days the water will become cloudy due to bacterial growth. The paramecium starter is then added. Over several days the paramecium will increase in number. They can be seen as tiny white "splinters" suspended in the water. The culture is fed a few dry peas every week or two. To feed to fry, some are drawn off with a baster and added to the fry hatchery. Paramecium cultures often smell quite bad for the first week or so. After that they become less objectionable. This author prefers not to use a culture until the "bad" smell, which is due to bacterial growth, has passed. Other hobbyists use corn husks to culture paramecium.Grindal Worms
Grindal worms are an excellent food for young fish, that is for partially grown fry. They are cultured in a similar manner to white worms, but prefer higher temperatures, about 70 °F being ideal. To culture them, prepare a bed of 50:50 potting soil and peat moss (sterilized by microwaving and allowing to cool). The mixture is thoroughly dampened with water until it is not quite wet. The starter is added and the worms are fed with a sprinkle of baby cereal daily. A piece of glass is laid on the surface of the culture and the box closed with a lid. As the culture develops the worms congregate on the glass sheet, and can be scraped off with a finger to feed. An alternative method for culturing grindal worms is to use plastic foam ("sponge") as the substrate. A suitable type is the "egg crate" foam often sold as mattress pad. A piece of this material is placed in a plastic food storage box, and water added such that the foam is damp at the surface. The starter culture is added and the culture fed with a sprinkle of baby cereal. The lid is placed on the box. Ideally, the inner surface of the lid will just touch the surface of the foam. The culture is fed lightly each day. After some days, worms will be seen congregating on the lid, where they can be collected for feeding to the fish. The advantage of this method is that there is no soil contamination and the cultures do not become invaded by house mites, which are a common problem in conventional grindal worm cultures, as well as white worm cultures.Breeding Killifish
In nature, killifish have adapted to biotopes in which other fish often cannot survive. In particular, many species can survive in areas where the water in ponds dries up during the dry season. In the aquarium environment, therefore, the hobbyist sometimes has to mimic these conditions in order to breed particular species. Some species of killifish lay their eggs in floating plants near the surface of the water, some prefer to spawn in deeper water, some do either or both; other killies spawn in the bottom substrate, some even diving deep into the substrate, disappearing from sight. The period and conditions required for development of the eggs also varies greatly. Some develop in water, others require a period of partial drying. Some require only a week or so to develop, others require more than a year and a half. One consistent factor in the spawning behavior of killies is that they generally lay only small quantities of eggs daily. Based on spawning behavior, killies have been categorized into three groups: plant spawners (top and bottom, including switch spawners); soil spawners; and soil divers.I. Plant Spawners
The plant spawners lay their eggs on floating or submerged plant thickets. They include many genera, such as Aphyosemion (most), many Fundulopanchax, Aphanius, Aplocheilus, Epiplatys, Pachypanchax, Fundulus (most) and Rivulus (except for Rivulus stellifer). In the aquarium there are several techniques that can be used to spawn these fish.The Mop Method
The most popular method of breeding plant spawners is the use of mops constructed from nylon or 100% acrylic yarn. The fish deposit their eggs on the strands of yarn. Organic yarns, such as wool or cotton, should not be used as they deteriorate in the water. The color of the mop does not seem to be very important, although some killie breeders claim that their fish prefer certain colors. Dark colors, particularly dark green, are often used. In all cases it is necessary to boil the mop before use. Construction of mops is not difficult. A cork, approximately 1.5 " diameter and 3/4 - 1 inch thick, is used for floating mops. A narrow groove is cut around the entire circumference of the cork. Next, the yarn is wrapped 30-50 times around a rigid piece of cardboard, or a book, of suitable size. The width of the wrapping should approximately equal the circumference of the cork. Several strands of yarn are then cut and threaded beneath the wrapped strands at one end. The whole thing is then slipped off and tied to the cork, adjusting the distribution of the strands uniformly around its circumference. Finally the strands are cut opposite the cork such that each strand hangs individually. This type of mop is generally better, and easier to search, than mops made by tying a bunch of strands into a knot at one end. For bottom spawning killies, mops are made by simply tying at one end, without the cork. When thoroughly wet, these mops sink to the bottom of the breeding tank. For breeding the mop is placed in a tank housing the breeders. The breeding tank is usually devoid of substrate, as many killies would choose to lay their eggs in the substrate. As many species of killifish will lay their eggs in either a floating or a bottom mop, one or each, or a long mop whose strands reach and lay on the bottom of the aquarium, may be used.