The genus Mogurnda Gill (1863) is a small group of benthic fishes inhabiting a variety of freshwater environments in Australia and New Guinea. The group contains at least six Australian representatives and about 20 species have thus far been recorded from New Guinea. Nearly half the New Guinea species are endemic to Lake Kutubu, Papua New Guinea. The remaining species are widely distributed throughout most of the mainland, but appear to be absent on the Vogelkop Peninsula at the western extremity of the island.
The Mogurnda genus is placed in the family Eleotridae, whose members are found around the world in tropical and temperate waters. Gudgeons can often be distinguished from other fishes by their elongated cylindrical shape. There is little chance of confusion between other species of gudgeons. Mogurnda can usually be recognised by their conspicuous red spots on a bluish background along their sides, often with a series of five to ten lighter or yellowish short vertical bars. Males, females and juveniles are similarly coloured. Most fins have red spots towards the fin base with a yellow outer band. They have a moderately large mouth for their size. The genus name is based on the Aboriginal word "mogurnd", which is a word some Aborigines use to identify this fish.
Australian species appear to be closely related judging from similarities in general morphology, colour patterns, and preliminary electrophoretic data. Colour patterns are useful for distinguishing species to a certain degree, but there is wide variation depending on habitat, behavioural moods and time of day. There is a distinct lack of unique features to aid species separation. Species are best distinguished by a combination of features including colouration, fin ray, scale, and vertebral counts. Geographic distribution is very helpful for identification purposes as there is usually only one species per locality. They are otherwise difficult to distinguish.
The Mogurnda genus in Australia was reviewed by Allen and Jenkins in 1999. They recognised three distinct species which had previously been included under Mogurnda mogurnda. The Finke Mogurndas have reverted to the earliest specific name which was applied by Zeitz to specimens from the Finke River: Mogurnda larapintae (Zeitz 1896). The Mogurnda populations in the Frew River and Whistleduck Creek in the Northern Territory are under taxonomic review and may be closest to Mogurnda larapintae, Mogurnda mogurnda or could be a distinct undescribed species. Genetic evidence suggests that there may be several more species in Australia than presently recognised. Therefore it is essential to take a responsible attitude to the problem of species identity, and ensure that aquarium populations of the different forms are kept pure, by not cross-breeding different geographical varieties.
New Guinea Mogurnda
Mogurnda aiwasoensis Allen & Renyaan, 1996
Habitat & Ecology
In general, water temperatures occupied by the Mogurnda species range from 15-36°C; pH 3.9-8.3; Conductivity 6 to 202 µS/cm. Fish from regions in southern Australia appear to survive at water temperatures as low as 10°C during winter. This range reflects the wide distribution of the Mogurnda species.
Very little is known about the breeding biology of Mogurnda in their natural environment. Most information is mainly based on aquarium observations. In their natural environment spawning usually occurs during the warmer period of the year (Spring-Summer) when water temperatures are around 19-34°C and food is abundant, which is often associated with rainfall/flood events. Juveniles typically inhabit the surface of pools during the day and shift inshore near structures as they grow. Larger individuals (20 mm+) take up benthic residence like adults, but commonly inhabit shallower habitat. Males reach maturity at a length of 45 mm, while females reach maturity at 49 mm. Young fish are more elongate than adults and become stouter as they grow.
Mogurnda are carnivorous and feed mainly on aquatic insects and microcrustaceans, but also consumes worms, tadpoles, shrimp and small fish (including their own species) as well as Gambusia holbrooki. They are also known to consume algae, pollen and miscellaneous forms of organic matter. Traces of oligochaetes, gastropods, teleosts, terrestrial plant material and terrestrial animals have been found in their stomachs. Mogurnda feed opportunistically in benthic and sometimes in the midwater zones of waterbodies.
Keeping & Caring
Good water quality, correct feeding, and adequate space are the main requirements which must be considered if Mogurnda species are to remain healthy and fertile. Water chemistry is not a major factor providing it falls within the tolerance limits of the fish. Treated domestic water is suitable provided extremes of pH and hardness levels are avoided. They appear to be comfortable if kept in water with a pH range between 6.8 to 7.5, and a general water hardness of up to 150 ppm. An effective biological filtration system is required to provide beneficial water conditions. For general maintenance in captivity they will accept good quality flake and bite-size pellet foods, although when attempting to breed these fish, a supplement of live or frozen foods such as daphnia, mosquito larvae or bloodworms to keep the fish in condition is a good idea.
In captivity, Mogurnda will regularly breed throughout the year if given appropriate conditions. Pair breeding is probably the preferred method for breeding them in captivity. When selecting a breeding pair, a female in condition to spawn will show a well-rounded abdomen with more intense colouration. Breeding aquaria should not be less than 50-L in size, and are probably best left completely bare with a small internal sponge or canister filter. A medium-size rock, small terracotta pot, driftwood piece, or a similar hard surface item should be provided for egg placement. Often the sides of the aquarium will be chosen. Pre-spawning activity in captivity has been observed at temperatures above 20°C, but a temperature range of 26-28°C would be more desirable for breeding. An artificial photoperiod of 12 hours light: 12 hours of darkness, or just normal daylength light, should be sufficient.
Spawning preparations by the male involves the careful cleaning of the selected site by removing all extraneous material. The female will visit and inspected the site on numerous occasions until she is satisfied with it. Once approving of the prepared site, she will placed herself in a horizontal position with her abdomen lying at an angle of about 45 degrees, so as to lay her eggs. The male will follow and with his head pointed in the opposite direction to hers, and his abdomen at right angles to the prepared site; will place his genital papilla immediately above that of the female and fertilise the eggs. The eggs are laid in rows, each having a sticky base by means of which they adhered to the spawning site. Immediately after spawning, the male will normally drive the female away, so at this time it is best to remove the female.
Females will spawn from 200 to 1300 elliptical transparent eggs measuring 2.0-3.8 mm in length and 1.0-1.3 mm in width. About 300 eggs is the average for young fish held under aquarium conditions. They can be laid in a single batch on a solid substrate, sometimes very close to the water surface on the underside of floating vegetation. Eggs adhere to the surface of the spawning site in a circular cluster via a sticky basal mass at one end. Spawning will be repeated over several weeks if the eggs are removed for separate hatching. However, removing the male prior to eyeing of the eggs will often lead to hatching failure.
Once spawning has been completed, the male will place himself perpendicularly above the eggs, frequently changing his position. He will begin fanning the eggs by oscillating his pectoral and caudal fins until they hatch, which can take between 3 to 8 days (148 hours at 26°C) depending on temperature. Within 3 days you should be able to observe the eyes of the fry as they hang by their tails encased in the oblong eggs. Before hatching, if you are lucky, you might actually see the bent body of the baby fish inside the egg roll over.
Newly hatched larvae are about 3.5 - 4.00 mm, with limited swimming ability. Feeding commences after the yolk is fully absorbed. Soon after hatching, the fry will start swimming and the male will stop taking care of them, so the male should be removed. The fry can be fed brine shrimp nauplii once they become free-swimming (about 48-72 hours) and grow quite rapidly if fed plenty of live food. It is important that the feed size increases as the fry grow until they are large enough to take regular aquarium foods. It can be advantageous to mix the sizes for a few weeks, especially if there is size variation within the fry. In two months they should grow to about 25 mm, in four months some coloured spots (very similar to their parents) will appear on the body. In another five to six months, at a size of 45 to 50 mm, they should be fully coloured fish. Young fish are more elongate than adults and become stouter as they grow.
Mogurnda species are attractive fishes which demand little, if any, specialised care but which contribute hours of fascinating observations. They deserve much more attention from aquarists than they have so far received. Gudgeons as a group offer the beginner and experienced hobbyist alike, a real challenge. There are a number of species in Australia, some still unidentified scientifically, that have yet to be successfully spawned and raised. They are not bred commercially and are rarely seen in aquarium shops. Some species are only available to the intrepid collector who is willing to go out and collect. Collecting is only the first step, the second and perhaps the most challenging part, is maintaining and breeding the fish once they have been moved from their natural habitat.
Adrian R. Tappin