Killifishes are most diverse in the tropical part Americas and Africa, especially in shallow or seasonal waters where other fishes are lacking. There are also killifishes in Asia, and the temperate parts of North America, Mediterranean Europe and the Middle East. Identifying species is not easy, and only a superficial review is made here. Many books have been published on keeping killifish in aquaria, but these tend to concentrate on the African and Asian species. For the European and American species you may need to refer to books on native fish faunas. There are also a number of killifish associations, some of whom have web pages. There are many advantages to belong to these associations beyond access to information, including the opportunity to get specimens of killifish not otherwise traded in commercially. One great feature of keeping killifish is that many species lay eggs which, if wrapped in damp moss or cotton wool, can be mailed around the world! In many cases it is also possible to catch specimens of native killifish yourself, but check your local fishing laws before hand. Some species are rare and protected in the wild. These should never be collected.
The most widely traded brackish water killifish is the Florida-flag killifish Jordanella floridae. This is a medium sized killifish, growing to about 6 cms (2.5 inches) in length, and rather deep and stocky. These fish occur in a wide variety of waters, not just brackish, so some care should be taken to allow the fish to adapt to the conditions of the aquarium. Otherwise they are active and hardy. As well as flake and small invertebrates, these fish should be provided with algae and other vegetable matter. Like many killifish, nibbling at algal growths ("aufwuchs") is an important source of food in the wild. Keep these killifish in a planted tank, but not too densely stocked since the males can be territorial. This is a subtropical fish and can tolerate temperatures up to about 20-degrees C (68-degrees Farenheit). A specific gravity of 1.002 to 1.005 is sufficient, and hardy varieties of Vallisneria and Sagittaria are similar enough to the natural plants of their native biotope. The closely related Yucatan pupfish Jordanella (Garmanella) pulchra needs similar conditions, but with more heat, between 22-28 C (72-82 F).
The American killifish of the genus Cyprinodon are more characteristic of salt water. While some occur in brackish and esturarine waters, others are found in inland waters made saline by mineral-rich streams or high rates of evaporation. Some of these fishes can be found in waters up to six times more salty than sea water. In general provide these fish with hard, alkaline water (pH 7.5 to 8) well buffered with coral sand or crushed shells placed in the filter. Most require plenty of warmth and a rich growth of algae on which to graze: a temperature of above 25 C (77 F) is essential as is bright light. Provide some cover for the fish with floating plants or rockwork. Avoid using materials, like driftwood, that might lower the pH.
Another American killifish found in a variety of waters are those of the genus Fundulus. These fish have been widely studied by zoologists because of their remarkable ability to adapt to different water conditions from freshwater right through to hypersaline water more salty than the sea. Fundulus heteroclinus is perhaps the best known. These fish are substantially larger than Jordanella or Cyprinodon, reaching as much as 15 cms (6 inches) in some cases. In shape they are streamline and rather like minnows without the upturned mouths of many other killifsh. They are quite predatory, taking small insects and crustaceans mainly but will eat small fish and eggs if they can. Otherwise they are peaceful and should be mixed with other quite fish. In the wild they are commonly found with fish such as mollies Poecilia and Mollienisia. These make ideal companions in captivity, since they are of similar size and temperament but prefer the upper part of the tank, while Fundulus tend to swim close to the bottom. Being subtropical fish these fish do not need quite so much heat as tropicals, around 20 C (70 F) being adequate, perhaps dropping by a few degrees in winter.
The European and Middle Eastern genus Aphanius is rarely traded but in many ways parallels the North American Cyprinodon in habits and maintenence. Some species of Aphanius are extremely colourful. An example is the lovely Aphanius mento in which the males are blue-black in colour with brilliant light blue spots. These fish should be snapped up when seen! In most cases the males are territorial and the fish should be kept in a large tank, around 80 cms (36 inches) long.
The Asian killifish of the genus Aplocheilus are among the commonest killifsh traded, usually known as "panchax" after an old generic name of one of the species. they are found in a variety of waters and will adapt well to slightly brackish water with a specific gravity of up to 1.005. These are fairly large killifish, up to 10 cms (4 inches) in length. They are distinctly predatory, and can easily eat fish of male guppy size. Kept in a well planted tank they mix well with fish too big to eat, such as glassfish (Chanda spp.), chromides (Etroplus spp.), and small spiny eels (Mastacembalus spp.) which all live in the same habitat.
The Asian bumblebee gobies Brachygobius are probably the most widely seen non-marine gobies in aquarium stores. It is a pity that so many are doomed to short lives, being rather difficult fish to keep well.
To keep bumblebee gobies well, three important rules must be observed. First, keep them alone. These are small fish which are likely to be bullied or even eaten by bigger fish. Secondly, provide lots of live or frozen foods. They will rarely take flake. Bloodworms, Daphnia, brine shrimp, and Mysis are all ideal staples which can be obtained cheaply frozen or caught live. Finally, keep the water well filtered with a strong but not turbulent current.
Bumblebee gobies will adapt to a range of salinties, depending on the species. Since they are so difficult to tell apart, a middle range set of values is probably best. Try a water temperature of around 27 C (80F), a pH of 7.5 and a specific gravity of 1.005. Keep the water hard using either chemical buffers or by incorporating shells or coral sand into the filter.
The best sort of aquarium for bumblebee gobies is of moderate size but thickly planted with either salt tolerant plants or plastic plants. Useful plants include Java Fern Microsorium pteropus, giant hygrophila "Nomaphila stricta", and onion plants Crinum thaianum. Allow these plants to form a thick tangle, which will help the gobies to feel comfortable. Driftwood and blackwater extract can be used (provided the filter is buffered to keep the pH high) to lend the water the peaty, dark quality characteristic of their swampy habitat. Decorate the bottom with large snail shells, such as those from apple snails Ampullaria.
Although bumblebees are best kept alone, in a good sized tank they can be mixed with other small fish. Ideal companions would be pipefishes, which also need live food.
There are a number of species of bumblebee goby, found from fresh to marine conditions. Three are imported regularly. The key diagnostic features are the "fin ray" counts and colouration, although the latter varies somewhat. Listed below are the three species most likely to be seen in tropical fish shops:
Brachygobius aggregatus is more restricted in range to the islands around the Phillipines and Borneo. It is found in fresh, brackish and salt water. The anal fin has one spine and six rays. In colouration it is basically yellow with four thick black bands, although the bands are not complete over the belly. The first dorsal fin is black. The second dorsal and the anal are transparent. This species should not be kept without salt in the water (a specific gravity from 1.005 to 1.010 recommended). It will even adapt to marine conditions.
Brachygobius doriae is a widely distributed fish found in fresh and brackish water. The anal fin has one spine and seven rays. Unlike Brachygobius doriae both the second dorsal and the anal fins are dark save for pale patches at the base. This species adapts best to freshwater, providing the pH and hardness are relatively high. This may be the same fish as the very similar Brachygobius nunus.
Brachygobius xanthozona is from Indonesia and Borneo and is found in fresh and brackish water. Similar to the previous species except that the anal fin has one spine and eight rays. Both of the dorsal fins and the anal fin are black except for small transparent triangular patches at the base of the second dorsal and anal fins.To spawn these fishes they must be provide with some sort of cave or burrow (a small flower pot is ideal). The fish form pairs, and are markedy territorial. During the breeding phase, the males become much paler in colour, the black bands weakening considerably and may vanish altogether. The female is very round when filled with eggs. The addition of cooler, fresh water often triggers spawning. The female lays the eggs inside the cave and then leaves the male to guard the eggs and raise the brood. The fry swim in the open water at first and will need tiny live food (infusoria) at first, graduating on to newly hatched brine shrimps. After a few days the fry settle down onto the bottom and swim rather less.
Another goby frequently seen is the violet goby Gobioides broussonnetii, a large eel-like goby from south-east United States through to northern Brazil. This fish needs a soft substrate to burrow into as well as a large tank. They appear to be territorial and are best kept singly except in a very big tank (over 180 cms, 6 feet, in length). While most gobies feed in midwater, these fish take foods from the bottom as well, such as worms, river shrimp, and mosquito larvae. Fairly salty water is required (specific gravity around 1.008).
An Asian goby often seen is the knight goby, Stigmatogobius sadanundio. This is found throughout South East Asia. Although it needs little salt (specific gravity of 1.001 to 1.005 is fine), it cannot adapt to soft, freshwater. Of moderate size, 8 cms (3.5 inches) it is peaceful and can be combined with fishes that stay in the middle and upper part of the tank. May take flake, but crustacea, worms and chopped mollusc meat should be a regular part of the diet. Also relishes algae.
Glassfish are small perch-like fish which are found in salt and brackish water around the coastline of tropical Asia and Australia. A number of the Australian species have become strictly freshwater fish, but are otherwise similar in needs to the brackish water species. They all need a quiet, well filetered aquarium and regular feedings of live food. They are a group of fish which appear not to do well on flake foods, even if they seem to eat them readily. Possibly some neccessary nutrient is missing. Many have exquisite transparent bodies within which every bone can be seen. In good condition they are among the greatest jewels of the aquarium.
Maintain in a planted aquarium, but with open spaces in which the fish can swim. A specific gravity of 1.002 to 1.010 is sufficient for most species, but by and large they will adapt to most conditions. An alkaline pH is important, as is a high degree of hardness. These fish need warmth, around 25 C (75 F) outside of breeding.
The common glassfish Chanda ranga is a small, compressed fish up to 8 cms (3 inches) long. It is found in India and Sri Lanka, where it inhabits a variety of coastal waters. Consequently it adapts well to a variety of conditions, provided the water isn't too fresh. Being rather timid, they prefer to be in good sized schools of around ten or more individuals. If kept in smaller numbers they can be very shy and refuse to feed. When healthy, the males develop bluey-white edges to the anal and dorsal fins. Keep the tank well planted if possible, using any hardy plants such as those recommended for bumblebee gobies. Common glassfish are quite easy to spawn when in good condition. The trigger is an increase in temperature to 28 C (84 F) together with sunlight, especially in the morning. Raising the fry is much more difficult. The eggs are scattered among plants and ignored by the parents; it is probably best to remove the adults and use an antifungicide in the tank. Feed the fry on infusoria at first.
Larger than the common glassfish is Wolff's glassfish,Chanda wolffi, which can reach 20 cms (8 inches). It is not as commonly traded, probably because it gradually becomes less transparent as it matures. Otherwise it is a handsome fish, but as yet not spawned in captivity. This is partially due to the rarity with which schools of mature specimens are kept. Being big fish, allow them a roomy aquarium.
The most delicate glassfish is also the most desireable. This is the filament glassfish Gymnochanda filentosa, similar in size and habit to the common glassfish but with the males possessing greatly extended anal and dorsal fin rays. Not as frequently spawned as the common glassfish.
The most commonly species traded are from Africa, where they are exported occasionally along with oddball gobies, dwarf cichlids and so on. None of the pipefish seem to be imported with any regularity and are well worth looking out for.
Mircophis smithi is a large species, up to 20 cms (8 inches) long and fairly robust provided it is well fed. It is able to eat guppy fry as well as crustacea. Keep in small groups of six to ten individuals in a well planted tank. The salinity need not be high (a specific gravity of 1.002 to 1.005 is adequate). A pH over 7 and at least moderate hardness is essential, as is good aeration of the water. These fish do not like turbulence, though.
Like seahorses, the males receive the eggs from the female. Although they lack a pouch, the eggs adhere to a region of the male's belly around which some swelling at least partiall covers the eggs. After hatching the male plays no part in protecting the fry, in fact he may well eat them. Freshwater pipefish are rarely bred in captivity, but since seahorses are spawned frequently, they would certainly make a suitable fish for the advanced hobbyist.
Livebearers do not form lasting pairs; after mating the male immediately seeks out new females. For this reason it is generally considered best to either the fish in single sex tanks except for mating, or else to ensure females outnumber by two to one or more. Otherwise the persistent attentions of the males stress the pregnant females and can cause miscarriages.
Besides the mollies discussed in part 3 of this FAQ, there are many livebearers worth keeping in the brackish water aquarium. However, the majority of livebearers offered belong to four species:
Fancy Mollies (Poecilia or Mollienisia hybrids)
These have been discussed previously. Most of the artificial varieties have very mixed lineages. They also tend to be quite delicate and short lived compared with wild (or at least feral!) varieties. An exception is the black molly, which is very robust, and will thrive in either brackish or marine waters.
Guppies (Poecilia reticulata)
Also know as Lebistes reticulatus. While many books might suggest this to be a hardy beginners fish, like the molly it has been heavily inbred to produce the fancy varieties many aquarists desire. As a result it is usually short lived and quite delicate, prone to white spot and rarely reaching the sorts of sizes seen in the wild. Broods are often smaller than normal. On the other hand, wild guppies (or domestic but not fancy varieties) are surprisingly durable.Guppies are not really brackish water fish, but will adapt well to lightly salted water and can be mixed with other quiet fish (a specific gravity up to 1.005). They appreciate bright, clear water with a definite current. Keep the pH above 7 and ensure the water is moderately hard. They will do well on flake but occasional feedings of mosquito larvae and bloodworms are very useful for conditioning fish for breeding.
Platies (Xiphophorus maculatus)
Platies are popular fish because of their small size and easy disposition. The common name, platy, stems from the old generic name for this fish, Platypoecilius. Like the guppy they are not strictly brackish water fish but will adapt to lightly salted water well (specific gravity up to 1.005). They need algae in their diet, either through regular feedings of 'vegetarian flake' or by encouraging algae growth in the aquarium.
Besides these four species, there are many species less often seen that make good aquarium inhabitants. Gambusia holbrooki is found throughout the southern USA and is cloesly related to Gambusia affinis which is restricted to Texas. Both are known as mosquitofishes. They are rather like guppies in habits but are more frequently found in brackish waters. They have been introduced throughout the tropics and subtropics where they can be found in a variety of waters. The females of both species look a lot like female guppies, being larger than the males (to 8cms, 3 inches) and quite plain yellow, green or silver. The males lack the gaudy tails of male guppies, but are similarly quite small, no more than 3 cms (1 inch) in length.Swordtails (Xiphophorus helleri)
Swordtails are bigger than platies, to which they are closely related. They can hybridise, so are best kept apart. Swordtails are more active and boisterous than many other livebearers, although are only of moderate size, 7 to 10 cms (2.5 to 3.5 inches). Males can be aggressive.
There is also a livebearer of quite different nature. The pike livebearer Belenesox belizianus is a highly predatory fish found in brackish waters through much of coastal Central America. Females are substantially larger than males, reaching 20 cms (8 inches) compared with the smaller males no more than 12 cms (5 inches) long. It relishes large invertebrates like river shrimp and worms, but small fish form the basis of its diet. It can be trained to take small dead fish, such as the frozen lancefish sold for other predatory fish. This may take some doing. Tying the small pieces of fish to cotton thread and dangling it enticingly in front of the fish may help. Hungry females have been know to eat the smaller males. Besides good feeding, planting with large robust plants can help the fish settle in. However, if kept with other big fish it is peaceful enough.
Most halfbeaks feed on surface insects, especially mosquitoes. They also enjoy bloodworms. With luck they will also take tiny pieces of prawn. Flake is rarely eaten.
Dermogenys pusilius is known as the wrestling halfbeak on account of the energetic fights males engage in. For this reason it is best to keep only one male in small tanks. The wrestling halfbeak comes from South East Asia and lives in a variety of waters, but appreciates lightly salted water. Like livebearers, the males have a modified anal fin for fertilizing the females. Once fertilized the female has a gestation period of up to two months. About 30 fry emerge.A specific gravity of up to 1.005 is adequate. Provide plenty of heat, at least 18 C (64 F).
Nomorhamphus liemi, the Celebes halfbeak does not need salt and should not be kept in a brackish water aquarium.
Xenentodon cancilia is not really a halfbeak but a type of marine gar. It is a large fish, up to 30 cms (12 inches). Both jaws are extended into long, needle-like jaws lined with sharp teeth. This fish is a predator. It is also quite timid, and should be kept in a school. It can be combined with bottom living fish well.
Since this fish is rather large, keep in a good sized aquarium at least 100 cms (3 feet long). Plant well to help the fish feel secure. Only a little salt is needed (a specific gravity up to 1.002).