leopards in your tank



Leopardfish Phalloceros caudimaculatus (Hensel, 1868)

This active, little livebearer was the first fish that I kept other than goldfish. In 1954, a friend and I caught a few specimens from a pond in the grounds of the local Doctor's residence, in Kent Town. Along with the goldfish and the aquatic Cassula species that I grew in an old concrete pond, Leopardfish began my adventure in aquaculture. They were raised in a well-planted, old, glass, battery-case and thrived - outdoors. The water reached daily temperatures over 35oC in the summer and dropped appreciably at night. The winter minimum temperature was near 4oC. A few fish always survived winter and numbers grew quickly each summer.

They took crushed food granules and thrived on algae, constantly mouthing the algal coat on the walls of the case. They eventually ended up in the pond and, like the goldfish, became food for marauding gulls. For sentimental reasons, I would like to keep some again but, unfortunately, this species has become a feral nuisance in parts of Australia and it is not sold in many Pet Shops. Phalloceros caudimaculatus has been introduced to dams and creeks as a mosquito control species (a role for which this species is unsuited) or by people releasing their former pets into the waterways.

Phalloceros caudimaculatus pair; female above, male below.  Note the long gonopodium on the male and the deeper body of the female.


The Leopardfish or Speckled Caudy, Phalloceros caudimaculatus (Hensel 1868), is a tiny, pelagic, non-migratory, livebearer (family Poeciliidae) and is similar in size and shape to the related Gambusia holbrooki, the Plague Minnow or Mosquitofish, but differs in colour and patterning. The body colour is silver, often tinted in yellow, and the males are distinctively speckled with irregular, black spots and blotches. Females  are less conspicuously spotted than the males and are much larger, growing to 4 cm and males to 2.5 cm in length. They are native to eastern South America between Brazil and Uruguay, in tropical streams, estuaries and still ponds with dense aquatic vegetation. In their tropical, native homes the water temperature ranges 20C 24C. Water conditions vary widely, from freshwater to brackish, with pH range: 7.0 8.0 and dH range: 9 - 19.

Leopardfish are hardy and tolerate a wide range of environmental conditions. They mainly eat plant material and sediment, extracting the micro-organisms that live there. Contrary to popular belief, they do not consume a substantial number of mosquito larvae and have little value in mosquito control. In South Australia, the River Murray Rainbowfish (Melanotaenia fluviatilis) is best used to control mosquitoes in dams.

Leopardfish are typical livebearers, giving birth to live young in broods of up to 80-100 offspring. That makes them prolific if conditions are right and a rapidly breeding pest species in our waterways.

Leopardfish can be an interesting aquarium subject if care is given to prevent release them into Australian waters. They are easy to keep and breed, can be kept in unheated aquaria (indoors) and adapt to a wide range of water conditions. They are best kept in a tank with a fine, gravel substrate and well-planted with Vallesnaria sp. and other aquatic plants, with some surface plant cover and with slow water movement. The water conditions are best if kept at 20C 22C, pH 7.4 - 7.6, in hard water to which a little salt (sodium chloride) has been added.

I have not kept these fish with other species and, unless they are fin-nippers, I think that they would be safe with fishes of a similar size such as Rice Fish, Zebra Danios or White Cloud Minnows in an unheated, indoor aquarium or with other livebearers in a tropical aquarium. They are active fish and forage by mouthing the tank surfaces, the substrate and plants in much the same manner as Guppies and Mollies. Feed them flake foods rich in green matter such as Spirulina Flakes or finely chopped blanched lettuce leaves. Frequent, partial water changes should be on a fortnightly basis, changing 20-25% of the water with fresh water adjusted to remove chloramines and chlorine.


In many places around the world, Leopardfish have been introduced into freshwater streams, ponds and swamps in the mistaken belief that they are a suitable species for the control of mosquitoes. In Western Australia they inhabit the swamps and drains of Perth metropolitan area. Phalloceros caudimaculatus is also reported from New South Wales where it is a pest species. In its Western Australian occurrences it is reported to compete with introduced Gambusia holbrooki and has replaced that species as a feral pest in some locations. Be very careful NOT to remove small fry at each water change and risk introducing them to our water ways.

If you acquire some Leopardfish please do not put them into dams and waterways but keep them securely inside your tank.

Put a Leopard in your tank and keep it there

The following advice comes from the Western Australian Department of Fisheries

"What You Can Do

To avoid the introduction of pests and diseases to our environment, aquarium fish, plants and animals should not be used for aquaculture purposes. They should be held in indoor aquarium tanks and never be released into any waterway or the ocean.

  • Do not allow any of your aquarium species, including fish, snails, amphibians, crustaceans and aquarium weed (algae), to be released, or to escape into any (local) aquatic environment.
  • Do not use the known invasive aquarium weed Caulerpa taxifolia as an aquarium weed species.
  • Unwanted live aquarium species may be returned to the aquarium dealer from where they were originally purchased.
  • Alternatively to dispose of aquarium fish, put fish and aquarium water into a plastic bag and into the fridge. When the fish stops moving, put the bag into the freezer overnight (endorsed by RSPCA WA Inc).
  • Other unwanted aquarium species and weed may be disposed of by placing them in the freezer for 24 hours.
  • Due to the associated risks, the Department of Fisheries does not support the stocking of ponds or dams with ornamental species and would suggest that native species are considered as a preferred alternative in these situations." Western Australian Department of Fisheries

Aquarium plants can be weeds, too, and introduced species ruin our native environment.  Read about aquatic, weed species.

An Educational Application in Keeping Leopardfish

Leopardfish make an ideal projects for schools. Keep them in at least a tank 60 cms long, 30 cms wide and 35 cms high (deep) that will hold 55 litres of water and weigh about 65 - 70 kgs when set up with rocks, gravel and water.  Set up with a fine, gravel substrate, an internal filter (read fishkeeping notes) and densely planted with some leaf-cover at the surface. A tank of this size can house several pairs plus a few extra females (it is best to have more females than males to avoid one female being chased by mating males).

Suggested activities:-

  1. learning to set up an aquarium and to care for a living creature. This project takes several months and involves establishing the tank and maintaining it and observing the fish.  Focus on establishing a correct habitat (use that word) and feeding routine. Older students could keep records of water conditions, monitoring temperature, measuring pH and total ammonia/ammonium and nitrite levels using test strips and NOT chemical tests.
  2. the monitoring of ammonia/ammonium and nitrite levels could serve as an introduction to the nitrogen cycle.
  3. teaching fish anatomy by observation (no dissections).
  4. observing a species in terms of habitat (where it lives), niche (what it does there) and reproduction.
  5. introducing the notion of "food chain"- plants are producer organisms and fish are consumer organisms. The concepts of niche and food-chain are connected and can be used to teach the notion of ecological interconnections in the "chain of life".
  6. teaching sex education- the biology of Leopardfish introduces "live-bearing" species that are not placental mammals.
  7.  introducing the topic of feral species and introduced pests (animals in the wrong habitat and niche). Consider the risks in using introduced species in ponds and dams.
  8. sample local waterways for pest species.
  9. pest eradication projects; contact Fisheries Departments and participate in pest control activities.
  10. population studies- growth rates; distribution.
  11. consider escape mechanisms, such as deliberate release, flooding and over flow from ponds, dams and streams, and how to prevent them.
  12. selective breeding- try to breed selecting for "all black" males or an increase in yellow colouring on the body. More than one tank will be needed.

Notes on Setting up Aquaria and Keeping Fish

Aquatic, weed species


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