Rainbowfishes (Melanotaeniidae) is a rather popular aquarium fish kind. It got the name due to the coloring which contains all rainbow dyes in the most unusual and unexpected combinations.
Nowadays there are 72 rainbowfish kinds known. All of them inhabit in Australia and neighboring islands.
Habitat in the wild
This group of fishes is relatively new in aquarium husbandry. It has become famous only since 1950s, at that most of the fish kinds have become available on sale only since 80-s.
The fish is almost not exported from the wild, to a large extent due to successful captive breeding and difficulties when transporting the fish from outlying regions. Besides in many of these regions some of the fish kinds are threaten with extinction.
The fish family got its name due to the dark stripe (melanos – means black, taenia – stripe), which stretches along the fish body and it is more or less visible regardless of the fish kind.
Rainbowfishes habitat includes waters of North Australia, New Zealand and Indonesia. These fishes act as a unique visiting card of Australia internal waters and its numerous neighboring islands.
At that about 50% of the fish family inhabit in the territory of Papua New Guinea, in River Mamberamo and Baliem.
Almost every year you can see new reports about discovering more new kinds of the rainbowfishes with unusual coloring. Natural habitats of the new fish kinds often intersect, however, at that there is no remote hybridization there: apparently, there must be some genetic barrier which prevents it.
Natural biotopes of fishes are quite diversified: these can be both shallow and fast flowing forest, mountain rivers and lakes or bogs, not only freshwater ones, but those with brackish water as well (up to 2-3 permille).
Water temperature in some waters during winter time may decrease up to 5-10°С, while in summer its value rises up to 35°С, while water temperature in other basins never gets lower than 22-23°С.
That’s why, it is desirable to be familiar with the conditions in which the fish you bought lives in the wild.
All rainbowfishes have elongated body rather flattened from sides and upward-pointing mouth with jaws having small coniform teeth.
As the fish grows its body shape changes rather significantly. This is especially true for the male fish, which become more deep bodied.
A distinctive feature peculiar to all fishes is that they have two dorsal fins very close together. The first fin is smaller, than the second one.
The fish size depending on its kind is in the range between 6 cm (2.4 in) (Iriatherina werneri) and 20 cm (7.9 in) (Melanotaenia vanheurni).
Body length of most of rainbowfishes is about 8 cm in average.
Difficulties in keeping
There are fish kinds that are easy to keep (Boesemani rainbow) as well as rare and demanding ones. As a rule, you can encounter undemanding and adapted species on sale.
Keeping in a tank
In the wild the fish dwells in quite different conditions and requirements to the tank conditions vary significantly for each kind.
Optimal tank water temperature for all rainbowfishes is considered to be 22-28°C (71-82°F) degrees.
The same is about tank water acidity and hardness which diverge greatly in various kinds of natural waters and they vary in the following range: for рН – from 4.0 to 7.0 and from 0 to 12 degrees for total water hardness.
Sometimes water hardness is up to 30 dGH high, which is due to large amount of dissolved salts that ingress into the water from the soil.
To keep and breed Rainbofishes in a tank there is no need for special water preparation. The only thing that matters, is the tank water quality in terms of toxic nitrogen compounds content in it. Excessive amount of the latter is not lethal for the fish, but it is highly unwanted.
Rainbow fish would do well in any tank not less than 100 liters (22 gallons) large for a group about 8-10 fish species. The larger is the tank, the better.
The fish demonstrates maximum of its coloring when it is kept in a spacious, elongated tank, which is thickly planted, but it also has some free space for the fish to swim as well.
Optimal tank conditions are the following: clean, transparent tank water with hardness from 7 to 25 dGH, рН 6,8-8,2 and temperature in the range of 22-30°С (average values are more preferable).
Since in the wild rainbowfishes prefer fast flowing waters, it will be reasonable to create some imitation of the water flow in a tank by means of a powerful water filter or a circulating pump.
As the fish prefers fresh water, it is desirable to renew ¼ of the tank water volume at least once a week (or more often).
It is recommended to buy grown up fish juveniles and not to look for bright colored adult fish species, unless it is very important for some reason.
Firstly, the juveniles adapt to new conditions easier. Secondly, adult fish species may bring some infections into your tank together with them.
Although, fish juveniles have less bright coloring, but it is more predictable. Usually, fishes are not imported, since local breeders provide them for sale.
Therefore, the fish you get is not enfeebled by the transportation process and it is also adapted to the water parameters in some specific region.
When putting rainbow into your tank you should keep in mind that the fish can jump well. When they play they often jump out of the water, so make sure that you have a proper cover for the tank.
You can decorate a tank with fishes using snags and long-leaved plants, which will be a shelter and a place to relax for the fish.
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Rainbowfishes are rather peaceful ones. They prefer company of their kind and they are good tank mates for most of tank fishes with only one exception, which is presented by slow and long finned fishes. Thay may nip their fins from time to time.
The more fishes are in the school, the less interest they show towards other fish kinds. They have enough things to do within the school. The situation is quite the opposite, if there are 2-4 rainbowfish species in a tank.
All rainbowfish kinds are schooling ones by nature and for this reason they prefer a company of their own, since there they feel much more comfortable. Therefore, it is desirable to have not less than 5-6 fish species in a group.
Since the fish males are much brighter and slimmer than the females, it is preferable to have more male fish species in a group.
When making efforts to attract female, the males try to show the best of them. Their coloring becomes brighter and more saturated and their movements are fast and graceful.
School prefers to swim in upper water layers, where the fish eagerly feeds on insects that fell into the water, which compose the main part of the fish diet.
Feeding is not a problem – they eat all types of aquarium fish food, both live and artificial ones. The fish prefers taking food from the water surface or in the depth, it rather seldom feeds from the tank bottom.
It is recommended to add plant food components into the fish diet, otherwise the fish may start to damage new leaves of some tank plants. Hungry fish can nip new soft leaves of aquarium plants, though not all of the fish kinds do this.
You should keep in mind that rainbowfishes are rather gluttonous, that’s why you have to control the food dosage. Because the fish doesn’t know when to stop and it can easily eat non-stop and fatal outcome is quite possible in this case.
Rainbowishes grow quite well when being fed with any type of live food. But you shouldn’t include fat food such as tubifex into their diet. Eating such food the fish get fat very fast and they lose their reproductive capacity.
Optimal Ranbowfish diet should include both live and artificial food. The diet based only on artificial food has also demonstrated good results.
The fish has rather pronounced sexual dimorphism. The male fish, as a rule, is larger and has brighter coloring than that of the female fish; also the fish body is noticeably higher, especially that of reproductive male fish species.
When the forepart of the fish dorsal fin is folded, it reaches the beginning of the dorsal end. The edge of dorsal and anal fin ends of the female fish species is usually more rounded, than that of the male ones.
The color palette of most kinds of females is shifted towards gray-brown colors.
At an early age it is quite challenging to define the fish sex. To avoid the situation when you have lots of unattractive female fish species in a tank, instead of bright colored male ones, the best option is to get the fish juveniles at the stage when their first signs of sexual dimorphism start to show.
If you can’t see these signs, it’s better to get a bit larger number of the fish than it is required. Later you can leave proper number of the fish in a tank depending on their coloring and sex.
Rainbowfish becomes reproductive at the age of 8-12 month old. As for the fish sexual dimorphism, it begins to show from about the age of six month.
For rainbowfishes breeding it is enough to have a tank 50-60 cm long. The determinal factor here is only the number of breeders put for spawning into the tank simultaneously.
As for the spawning substrate, you can use several bushes of small leaved aquarium plants (Java moss) and put them along the walls or in the corner of the spawning tank.
Tank water parameters don’t have any crucial significance, but it is rather preferable that the water is soft close to the neutral pH value.
The number of male fish species in the group of fish put for spawning should be slightly bigger, than that of the females.
It’d be rather helpful to keep the breeders separately before spawning, since this shortens the spawning time and allows obtaining the largest possible amount of eggs in 2-3 day period.
Diversified diet and high feeding during this period as well as frequent renews of sufficient amount of tank water will also stimulate the spawning process.
Rainbowfishes spawn in portions. Every day during one or two weeks the female fish lays from 5 to 50 eggs on the plant substrate or caprone threads, then there is a break that lasts for couple of weeks.
The breeding group consisting of two females and three male fish species can lay from 200 to 300 eggs in a week.
Eggs on the plant substrate are rather small at the beginning, but soon they will swell and grow to be up to almost 1.5 mm in diameter. Total number of the eggs is defined by the time during which the breeders stay in the spawning tank (from 2-3 to 7-8 days), their condition and number.
The eggs stick to the substrate by means of filamentary shoots. Since the breeders are capable of eating their eggs, they should be moved together with the substrate into another tank filled with water having the same parameters for further incubation.
The temperature in the incubator should be maintained constant ( ± 1°C), besides moderate aeration is also required. It is possible to add a small amount of some fungicidal agent into the water, for example, methylene blue.
Due to the fish size and sensitivity its embryos are quite susceptible to many kinds of organic and inorganic compounds dissolved in the water.
That’s why one of the most important conditions of successful breeding is high water quality.
Eggs of the most rainbowfishes don’t develop at daylight. For this reason, lighting in the spawning tank should be dim.
All rainbowfishes have one interesting peculiarity. Unlike other fishes, their larval stage occurs in the eggs. And when juveniles hatch from the eggs, they are already able to feed and swim actively.
Usually about 7-10 days pass from the day of laying eggs till the time when the juveniles hatch. You can keep the adult fishes in the spawning tank till the first juveniles appear. Rainbowfishes don’t eat their eggs, but the chances are high that they may start eating the juveniles.
Newborn juveniles gather is large groups near the tank water surface, where the lighting is more intensive.
The fish juveniles are rather small sized. As a start food for them it’s better to use artificial food for aquarium fish juveniles, later it can be brine shrimp nauplii.
At that, growing the juveniles by feeding them with artificial food quite often has better results, then in case of natural microplankton diet. The thing is, that at early stages juveniles are more demanding, than grown up juveniles and adult fish, and they often refuse to eat at all if you give them nauplii of some other kind.
The fish juveniles grow unevenly, that’s why you should sort them from time to time. Otherwise, larger fish species may eat their smaller fellows.
For the same reason, it’s not a good idea to keep juveniles of different ages in one tank.
Paul Townsend is a founder and author of Meethepet.com. He’s been fond of aquarium husbandry since his early childhood.
His favorite aquariums are biotopes (Amazon River), Echinodorus and Angelfish. However, through the years he’s had experience of keeping almost all types of freshwater fish and shrimps.