Colourful and hardy. Peaceful and prolific. Rainbow fishes from northern and eastern Australia and New Guinea have experienced a deserved upsurge of popularity in recent years. This trend has undoubtedly been closely linked to the improved availability of a far greater number of species than before. Farm raised stocks of the Australian Rainbow, or Dwarf Rainbow (Melanotaenia maccullochi) and the Blue Rainbow (Melanotaenia lacustris) have been shipped out from Far East fish farms for many years. The beautiful Madagascar Rainbow (Bedotia geayi) has also been spasmodically available to the hobby for many years, often from eastern European breeders. The Celebes Rainbow (Telmatherina ladigesi) from Sulawesi is another delightful species which has been only occasionally offered to the fishkeeper until more recent times. Now these and other highly desirable species of Rainbow are almost routinely available from a number of commercial suppliers. One time the Rainbow fishes were considered to be members of the same family of Atherinidae. However, those in the genera Melanotaenia, Glossolepis, and Iriatherina, offered quite regularly to the modern hobby, are currently reclassified to the separate family of Melanotaeniidae. Less often seen Silversides of the genus Quirichthys remain classified in the family Alestidae. This explains why older references may cause some confusion with conflicting classifications being recorded.
Both Australia and New Guinea share a common dearth of interesting freshwater fish life. The adjacent Malay/Indonesian archipelago by contrast hosts an enormous range of freshwater fish species. This puzzling fact is perhaps explained by the existence of Weber’s line, a deepwater channel which isolated the two areas from each other and prevented the migration of freshwater fish. On the other hand, New Guinea and Australia were linked by a land bridge as little as 6000 years ago, enabling some species to have lived in both territories and survive into modern times. Rainbow fish are not exactly prized fauna in either land. In Australia they are valued mostly as bait fish by anglers, and in New Guinea they are dried and salted as food fish.
The main natural locations for Rainbow fish are remote and difficult to access. Restrictions on collecting fauna native to Australia are quite severe, and licensing is far from automatic. It is true to say that those species found on sale in aquarium shops in Australia will mostly have been imported from fish breeders in Singapore or Indonesia. Some species are found in wildly differing locations. For example, the Splendid rainbow (Melanotaenia splendida), can be found in bore holes in the arid central region of Australia. It may also be found in steamy jungle streams of New Guinea and a range of environments between the two extremes!
The genus Melanotaenia offers the fishkeeper a range of Rainbow fishes with little variation of body and finnage shape. The typical body form is a fish with a fairly deep “keel”, relatively smooth, flattish upper profile, with a double dorsal fin. The forward dorsal fin is about a third or less the size of the trailing second dorsal fin, almost giving an appearance of a single complete dorsal fin which has been damaged. The anal fin base extends from about midway along the lower body to terminate just short of the caudal peduncle. The mouth is set at the tip of a pointed snout. However, there may be a considerable change of the overall body shape as a specimen progresses from a juvenile to adulthood. Some species start out with a streamlined form but take on a very much deeper, stocky appearance with maturity. A good example of this is seen in the development of the New Guinea Rainbow (Glossolepis incisus). Horizontal line markings ornament the bodies of most species. Some of these will follow the lateral line prominently, often accompanied by further linear markings above and/or below. Others have a series of lines in differing colours, and positioned more randomly. Those species which are predominently spotted have the scale markings arranged in such a way that they continue to give the impression of horizontal lines.
A comparative newcomer to the hobby scene is the Peacock rainbowfish (Melanotaenia praecox). No sign of line markings on this very beautiful fish. The clear sky-blue body sparkles magnificently, with conspicuous scale definition providing the sole form of body markings. This blue metallic mirror effect is superbly complemented by the brilliant red which suffuses all finnage except the completely transparent pectoral fins. Unlike the majority of its close relatives this species shows attractive colours even as a juvenile. Although the Peacock rainbowfish made its debut to the hobby at quite high prices it has proved to be a free breeding species and will surely become relatively inexpensive in a short time. Already F.O.B. prices from Far East suppliers have dropped significantly. It is reasonable to assume that this lovely fish will become a front runner in the popularity ratings for ornamental tropical fish, destined to delight future generations of fishkeepers. A “classic” for sure!
Approximately 12 – 16 species of Rainbow fish are frequently available to the fishkeeper. Some of these are almost routinely available, while other may be more occasionally seen. Wild caught fish from Indonesian supply sources provide some fine and interesting species, but domestic breeding is expanding to provide the market with a more constantly reliable supply. Unfortunately there are a number of hybrids originating from some commercial breeding sources. Even in the wild hybridization takes place. These hybrids are undoubtedly handsome fish, and it is of little consequence to the aquarium keeper that they are not pure bred species. But for the serious fish breeder the acquisition of “uncontaminated” stock of a known pure lineage is important.
There seems to be no seasonal influence affecting the breeding cycles of Rainbow fish, as they are seen to spawn throughout the year. They prefer to have a well planted aquarium with thickets of fine leaved plants where the females will deposit a small number of eggs on an almost daily basis. Breeding males develop a broad metallic stripe of colour running from just before the dorsal fin, over the head, and down to the tip of the snout. The eggs are adhesive, attaching to the plants by means of a filamentous thread. They take quite some time to develop and hatch, ranging from one to almost two weeks for the process to complete. Some species have light sensitive eggs and maintaining low light levels is necessary to achieve success. Newly hatched fry are able to take very fine dry foods right away. Growth rates are generally not fast and a good feeding regime is essential to achieve the best possible progress. However, sexual maturity is often attained after just one year. Soft water conditions are not recommended for breeding purposes as these species prefer a medium hardness with a neutral to slightly alkaline pH. Water temperature of around 25 degrees C. is fine – one or two degrees above or below will present no problem. Live foods, or defrosted frozen “fresh” foods, are recommended to form an important part of the overall feeding regime when conditioning the fish to prepare them for breeding. For less specific maintenance a good nutritious diet will suffice, but an interesting variety of foods will always produce the reward of a better looking fish. Remember that in their natural environment rainbow fishes eat aquatic insects, crustaceans, and algae. Such fare even occasionally offered to captive fish will provide a special treat.
As community fish the various rainbows are ideal. They have a peaceful temperament, showing tolerance towards even comparatively tiny companions – providing they are larger than mouth-size, of course! Anything small enough is at slight risk of being snapped up but not typically so by rainbow fish. They are not generally boisterous fish, tending to move gently about the aquarium. Plant eating is not a known vice either. They do not dig or defend territories. The reflective nature of their bodies is capable of radiating a spectrum of colour from many species. Some front lighting is necessary to achieve the best colour rendition. It is interesting to note that fully mature specimens are rarely taken from wild collections. This fact coupled with the early sexual maturity of the young fish suggests that predation prevents reasonable numbers of the species reaching full maturity, limiting their expected lives to an estimated range of one to four years in the wild. In aquarium culture a lifespan up to eight years is not unknown.
The lovely little Threadfin Rainbowfish (Iriatherina werneri) is almost in stark contrast to the Melanotaenia species. The outstanding feature is the extensions to the anal and dorsal fins of the mature males. These extensions to the first few rays of the fins trail back in a graceful array to terminate in line with the finely tipped ends of the deeply forked caudal fin. The body of the male frequently shines metallic blues, greens, and a coppery iridescence, while the fin extensions of the dorsal, anal, and caudal fins may vary from sooty-black to carmine-red. The female lacks these embellishments of both fancy finnage and pretty colours. This species also carries the paired dorsal finnage, but this feature and the body form being a streamlined torpedo shape is quite different to that of the genus Melanotaenia . A well planted aquarium is the preferred environment for this elegant fish. An acidic pH for breeding is required by the Threadfin rainbow. In nature they are found inhabiting densly weedy areas in the shallows of swamp land, where the eggs are deposited, taking about 12 – 15 days to hatch.
The Celebes rainbowfish (Telmatherina ladigesi) has been known to the hobby for more than 50 years. Coming from remote areas of the Indonesian island of Sulawesi (formerly Celebes) this fish had a reputation for being difficult to acclimatise to aquarium conditions, reacting very badly to even quite slight changes in water chemistry. This hardly seems to be the case today when the stock available to the aquarium hobby is almost exclusively commercially bred. The claimed sensitivity to water conditions may have been largely bred out (?). Hard water with a neutral pH is the aim when setting up a breeding tank for the Celebes rainbow. Soft water will not be suitable. Some plants affording a degree of cover will be appreciated, with floating plants in addition if available. When the male displays to the female his true beauty can be seen. The ornamental fins are spread widely, with elongated filaments splayed like fine fingers from both anal and dorsal fins. A golden edging to the lower body and dorsal area extends into the upper and lower edges of the forked caudal fin. The tip ends of the tail are emphasised with white flashes. The leading fin of the paired dorsal finnage spreads like a little fan. Burnished golden tips to the pectoral fins and an electric-blue flash of colour running from midway along the lateral line down to the caudal peduncle, complete the display. The female is similarly coloured, if more muted, and she lacks the fancy finnage extensions. This is a shy fish and needs a peaceful tank without any hassle in order to flourish and breed.
Home for the Madagascar rainbowfish (Bedotia geayi) is far removed geographically from the previously mentioned species. This is a fish of quiet beauty. It is almost unknown for it to be anything other than entirely placid. A perfect community fish. The outstanding features are the brassy metallic areas which shine out from its flanks, and bright red areas, the bottom of which are edged with ebony-black, decorating the caudal fin of the male. A red edging underlined with black reflects this feature in the anal and dorsal fins of the mature male. Flashes of bright gold also sparkle from these two fins. Like all the other Rainbowfish this species also carries the double dorsal fin. Slightly alkaline water is preferred. This is one of those species of tropical fish which may be kept in a single species tank where they usually breed continuously without eating their eggs or molesting their fry. Commercial supplies of this beautiful fish were once quite restricted, mostly coming out of eastern Europe. But the supply situation has changed quite radically over the past few years with good supplies now coming out of the Far East, particularly from Indonesia. A strongly coloured “giant” strain has appeared in very recent times and is surely destined to replace its smaller ancestor in time (?).
Strictly speaking my last species is not correctly a Rainbowfish, but is so often associated with them and in many ways similar maybe it is not out of place within this article. This is the Strawman (Quirichthys stramineus), a Hardyhead or Silverside embraced by the family Atherinidae. The paired dorsal fins feature again. The body scintillates shimmering green scales, but it is the finnage which is so distinctive, especially and predictably in the male. Only the pectoral fins are clear and quite devoid of any colouring. The forward fin of the paired dorsal is dark at its base but radiates out to its edges with a bright golden flare. The larger posterior dorsal fin is a charcoal colour with rays reflecting golden glints culminating in a fully golden trailing edge tipped with white. The caudal fin is fully edged with gold, and displays the same glints of metallic gold as the dorsal fin. The anal fin and ventral fins also have the golden edging but the fin rays are strongly represented with gold. It is found both in running streams and still lake waters in Australia. Care and breeding habits are similar to those detailed for the “real” Rainbowfish described above. The water for breeding stock should not be too hard, however, and a neutral pH value is best aimed for.
I hope this modest overview of these quietly mannered fish will make you look more closely at them when seen in your supplier’s stock tanks. Some will display pleasing colours even as juveniles, but others may need time to slowly blossom forth in their full glory in your care. With their many attributes and few drawbacks the Rainbow fish could be on anyones shopping list.