Wild Mollies in New Zealand
by David Cooper
of New Zealand
New Zealand, being a temperate country, at least weather wise, is not prone to having
feral populations of tropical fish. (Although the same cannot be said of cool water
However there is at least one exception, the Green Sailfin Molly, Poecilia latipinna.
These were introduced in to a thermal swamp in the Central Plateau of the North Island by
persons unknown at least 30 years ago. This population is relatively unknown, except among
fisheries scientists and some aquarists. They are confined to a relatively small area of
warm water and predators are kept away by that same warmth. They are not considered a
threat to the environment and so apart from an occasional aquarium society out for a jaunt
they have been left undisturbed.
These fish have acquired the status of an "urban legend" among keepers of
tropical fish in NZ and even though I have been aware of them for at least 20 years and
been heavily involved in the aquarium industry in NZ, I have never actually seen one. In
my new job as manager of the NZ National Aquaculture Centre I am responsible for building
a collection of live fishes that tell the "NZ fish story" and as there were
other fish in the area that I needed, a trip was soon organised.
In the company of my friends Paul Woodard and Mike Harvey, both ex presidents of the NZ
Native Freshwater Fish Association and armed to the teeth with every net and trap known to
man we set off in mid January 2004.
The thermal swamp where Green Sailfin
Mike has been to this spot before, which was just as well as we would never have found
it alone. To say that there are plenty of Mollies present is a gross understatement. I
have never seen so many fish in one spot before, not even Gambusia, which we thought they
were at first. Using 5 Gee Minnow Traps we caught approx a thousand fish, most of which we
A beautiful Green Sailfin Molly, Poecilia
The fish ranged in size from very small to approx 40mm and there were no sick or
deformed fish caught. The water as pH 7.6, KH 17, GH 11, PO4 1ppm and the temperature was
about 26 C although this was just a guess as somebody (me) forgot to take the thermometer!
The water is only about 200 to 300mm deep and the bottom is soft mud that appeared to
be very deep. Poor access and a healthy fear prevented us testing the substrate's depth.
The only aquatic plant present was Raupo (Typha orientalis) and there were great rafts of
filamentous algae (probably Spyrogyra sp.) No prizes for guessing what these fish eat!
The only margins that were not blocked by dense Raupo growth were heavily overgrown
with Brambles. This of course made access quite exciting. Talk about bleeding for your
The area of swamp was approx. one acre and the Mollies were not in the top part,
presumably as it was too warm. The bottom end of the swamp where it meets the adjacent
lake cools rapidly and within a few meters the mollies disappeared. (Zillions in one trap,
two in the trap a few meters away and cooler.)
Apparently there used to be Swordtails in this same swamp but these have since died
out. There is also a thermal stream (Waipahihi Stream) about 50 km. away from the swamp
where there were also swordtails. We did check and left traps overnight but these appear
to no longer be there.
The 200 or so fish we brought home are doing well and doing what Mollies do (eating and
reproducing) in an aquarium in the Aquaculture Centre holding facility. There are only
about 10% males, if that and they appear to be more vigorous and robust than the specimens
available commercially. Having just tried to catch some from the tank I can attest that
they are certainly faster moving than any Molly I have ever encountered!
If you are interested to know more you can email me at firstname.lastname@example.org If you would like to know about the NZ
Native Freshwater Fish Society look at www.nzfreshwater.org