Rainbowfish Identification | Melanotaenia

After nearly three months out due to ill-health, I was finally back on the road and heading up to see my good friends at the Kirkcaldy Aquarist Society. The purpose of this visit was to do a presentation on Rainbowfish Identification and it seemed to go down well with a very healthy attendance. Identifying Rainbowfish can often be very difficult even to the most experienced aquarist; just pop into your local fish store and have a look at the often drab colourless young fish you will encounter.

The common problems leading to this difficulty include: 1) Wrongly labelled fish, 2) Hybrids, 3) Lack of furnishing in dealers tanks, 4) Young sexually immature fish and 5) The number of similar species.
In my lecture I showed how Rainbowfish groups can be identified by shape as well as by colour. For example the Southerly “Nigrans” group all have certain characteristics such as a slender stream-lined body, typical of a riverine species, whilst the Southern “Australis” group are mostly high backed species with flowing dorsal and anal fins.
Melanotaenia splendida ” Coomalie Crater”, Part of the Southern “Australis” group.

During my lecture I concentrated on the southern lineage fish, Goldiei, Maccullochi, Australis and Nigrans. This group of fish have a closer relationship than you may think. They may inhabit the rivers of Australia, the Aru Islands and New Guinea and be separated by the sea, but 10,000 years ago during the last glacial lowering of our sea levels the Islands were all connected by what we call the Sahul shelf and formed the great continent of Sahul.

Many people believe that some of the Southern rivers of New Guinea and the Northern rivers of Australia flowed into a lake called Lake Carpentaria which was replaced by the Arafura sea and the Torres Strait as the sea levels rose but at one time these fish all inhabited the rivers that flowed into the same lake hence the close relationship.
The dotted lines show the former land bridge that connected Australia, the Aru Islands and New Guinea during the last ice age. Lake Carpentaria shown in white is believed by many to have drained west before emptying in to the Timor sea
The Goldiei Group
Melanotaenia picta was formerly known as M. sp “Aru II” until its recent taxonomic description

Found in Australia, the Aru Islands and the Island of New Guinea, the Goldiei group is large with species such as Melanotaenia trifasciata having many different colour forms based on geographical location. More study is needed and we may see these being split and new species being created. All the group show the same identifiable characteristics such as a dark mid lateral band and high arched back though this may vary in intensity with differing species. Species can vary in size from 7cm to 20cm.Goldiei group species can be recognised with its 2nd dorsal and anal fin hugging the body of the fish and both are more or less symmetrical in shape.

Melanotaenia trifasciata ” Habgood River” Part of the Southern Goldiei group.
Melanotaenia trifasciata “Goyder River”. A young specimen of around 9 months.
Melanotaenia goldiei.

The Australis Group
Found mainly on Australia apart from two New Guinea species, M. rubrostriata and M. parkinsoni, The Australis group much like the Goldiei group, contains species with many different forms based on geographical location. Most fish in this group are riverine species and attain lengths of between 6.5cm and 16cm. The Distribution of the Australian species in this group is by far the largest of any of the groups with species being found in the central and northern coast of eastern Australia, along the northern coastline, down into central Australia and out to the north western coast. Of the two New Guinea species M. Rubrostriata is the most widespread and can be found in most creeks from the Mighty Fly River catchment area in Papua New Guinea and westwards to Etna Bay in West Papua.

Melanotaenia rubrostriata, from the Kopi River, West Papua
Melanotaenia rubrostriata “Fly River” Papua New Guinea.
Melanotaenia parkinsoni, from the Kemp River, Papua New Guinea.
Melanotaenia splendida inornata, from the Coomalie Crater, Australia

The Maccullochi Group
A dwarf group of fish from the island of New Guinea with the exception of Melanotaenia maccullochi which can also be found in Northern Australia, highlighting the Sahul land bridge connection. This group seems to be becoming more available to the hobby with such fish as Melanotaenia ogilbyi being rediscovered and the stunning find that was Melanotaenia garylangei. One fish, Melanotaenia papua still regularly appears on import lists but sadly the fish always turns out to be M australis; Fish of this group grow between 6-8cm in length.

Melanotaenia sexlineata
Melanotaenia ogilbyi
Melanotaenia maccullochi

The Nigrans Group
Fish of this group can only be found in Australia. M. nigrans, M. gracilis and M. exquisita originate from the far north while M. pygmea can only be found in two small tributaries of the Prince Regent River in North Western Australia. These fish have a stream lined elongated body typical of a stream dwelling fish.

Melanotaenia nigrans, from Pago creek, Australia

Melanotaenia pygmea from Prince Regent creek, Australia

Hybridisation
Hybridisation is very common within Melanotaeniids in captivity,this is most likely down to their young evolutionary history. Rainbowfish hybrids are commonly offered in our pet stores under such names as “Pigeon Blood”, “Marci” & “Yellow Pyjamas” to name a few. Fry from a community of mixed Rainbowfishes should not be saved and should never be raised and sold or passed on to other enthusiasts. Gudgeons like Tateurndina ocellicauda are a good addition to prey on new born fry. Geographical variety’s such as Melanotaenia trifasciata “Goyder River” and Melanotaenia trifasciata “Cato River” for example should also be kept separate as these could one day be separated into different species.
A typical hybridised Rainbowfish.

Hybrid Rainbowfish can also become very large and aggressive and a term is applied to such fish called “Hybrid vigour”. The aggressiveness is down to the increased vigour and health and resistance to disease these fish display and bullying can become out of control within the community set up. Hybrids in my opinion have no place in the hobby.

Male Tateurndina ocellicauda often predate upon Rainbowfish fry

Written by: Alex Carslaw | Editor: Chris Englezou
Picture creditsAlex Carslaw | Wallace Tao |George Funkner | Mark Shaw | Leo O’Reilly | Matt Chilton |Dave Crossett

Alex Carslaw is without doubt the U.K’s most dedicated Rainbowfish enthusiast – award-winning in fact and he has made it his passion to become a significant contributor to the field in hope of preserving both their keeping in the aquarium hobby and in many cases stabilizing a future for several species of these graceful, diverse and unbelievably underappreciated fish. Alex has been keeping and breeding fish for just over 30 years and his passion for Rainbowfish began with a consigment of the stunning Melanotaenia boesemani which he encountered when working for a Glasgow importer of tropical fish. Alex is a great believer in the power of social media and has used this platform to create a worldwide network of Rainbowfish enthusiasts through his Facebook group and personal website. Alex’s work, whether his hours upon hours investing time & money into his fish, or researching, learning and teaching others about the wonderful Rainbowfish of the world, helps to keep raising awareness for many Rainbowfish which are in urgent need of protection. Some of these species originate from single lakes in what are now ‘developing areas’ and hence being destroyed, polluted or filled with invasive species which are outcompeting or even predating upon these pressurized populations. For some of these fish, their propagation within the aquarium hobby is their only chance to remain on earth.

Alex Carslaw

Alex Carslaw is without doubt the U.K's most dedicated Rainbowfish enthusiast - award-winning in fact and he has made it his passion to become a significant contributor to the field in hope of preserving both their keeping in the aquarium hobby and in many cases stabilizing a future for several species of these graceful, diverse and unbelievably underappreciated fish. Alex has been keeping and breeding fish for just over 30 years and his passion for Rainbowfish began with a consigment of the stunning Melanotaenia boesemani which he encountered when working for a Glasgow importer of tropical fish. Alex is a great believer in the power of social media and has used this platform to create a worldwide network of Rainbowfish enthusiasts through his Facebook group and personal website. Alex's work, whether his hours upon hours investing time & money into his fish, or researching, learning and teaching others about the wonderful Rainbowfish of the world, helps to keep raising awareness for many Rainbowfish which are in urgent need of protection. Some of these species originate from single lakes in what are now 'developing areas' and hence being destroyed, polluted or filled with invasive species which are outcompeting or even predating upon these pressurized populations. For some of these fish, their propagation within the aquarium hobby is their only chance to remain on earth.

One thought on “Rainbowfish Identification | Melanotaenia

  • 2nd April 2017 at 10:17 pm
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    Loved reading this Alex.

    Reply

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