Backyard Aquaponics
A place to discuss aquaponics

Beggers cant be choosers in the bush, Roz.

Mind you, come to think of it.... the yabbies might have cleaned them up.

That is definitely possible... I have seen small fingerlings with the tails nipped right off by yabbies... when I had them in the same tank..

Hi CraigSalt,

just a bump re your idea for a black poly pipe heater. I used one this last winter which worked quite well. I coiled 100m of 13mm pipe around a wire mesh frame (made into a flattened cylinder approx. 1m. high and 50cm diam. placed on a wooden stand and angled to be perpendicular to the winter sun). I put the base frame of an ibc behind it (flat baseplate removed), also with mire mesh in the shape of a parabolic reflector and covered it with a sheet of sibilation to reflect back onto the coiled pipe. A small pump is connected in the fish tank, the other end above water level (to stop back syphoning at night). The pump is powered by a 20W solar panel, so it only runs through the day.
I was able to maintain about 4C above a second system without a heater, which was enough to keep the SP's eating through winter.
Wish I was able to show a photo, but I have had no luck uploading photos...too bloody slow at learning how I think.

PS. Another possible culprit for your disappearing fish is a Rakali (or native water rat: Hydromys melanogaster). They can smell fish from a long way away, are very clever at figuring out how to get at their desired food and usually attack at night. They also tend to prefer a raised feeding spot (a rock, bench or raised patch of soil) where you might find some fish scales or other remains. If you live near a lake, the sea or creek/river, this may be your culprit.
Behaviour wise, they are very much like otters....cute and playful animals, until they find your fish!