The fish tank temperature plays a fundamental role in determining how active our fish are. Fish, unlike mammals and birds, are unable to control their own body temperature. They are scientifically referred to as poikilothermic. Their metabolism reflects the temperature of the water in which they live. As a consequence, they will show a wide range of responses to all biological processes such as feeding and breeding according to the temperature of the water. But what is the best temperature to keep our fish.
Low temperature result in low feeding and growth rates. Below 10 C. a carp will rarely attempt to feed and certainly would not grow however much food is available. At 12 C. carp will start to show some interest in food but will not grow appreciably until the temperature exceeds 15 C. Rather more surprisingly the temperature at which carp grow fastest is a tropical 28 C. A temperature rarely experienced in the UK. Perhaps more importantly a caro will convert its food most efficiently at a temperature of around 25 C. I have always maintained my carp systems at 24 – 25 C. when maximum growth rates have been the main objective.
Optimal fish tank temperatures
Each species of fish will have specific temperatures at which feeding starts, growth is at a maximum, feed conversion is optimal, spawning takes place and death occurs. The control of water temperature is therefore a vital parameter if optimal growth is wanted through out the year. This is certainly not something you have to achieve. Seasonal variations are the norm and heating fish tanks to 25 C. in the winter can be prohibitively expensive. Carp in outdoor ponds in the UK usually take 3 years to reach 1kg. In the tropics the same size can be achieved in something approaching 10 months.
|Species||Optimum Temp. C.||Tolerable Temp C.|
|Trout||14 – 16||10 – 18|
|Goldfish||18 – 20||6 – 26|
|Fancy Goldfish||22 – 26||16 – 18|
|Carp, koi||24 – 26||12 – 30|
|Tilapia||28 – 30||20 – 35|
|Channel Catfish||28 – 30||20 – 35|
Heating is the only way to maintain suitable temperatures for many of our favourite aquaponics fish. Cost is the overriding problem. Although it is cheaper to heat a fish tank than to cool it careful design is essential to stop energy costs spirally out of control. The following points are well worth considering.
- good insulation is paramount to minimise heat loss
- minimum influx of clean, unheated water
- minimum tank volume
With adequate insulation it is perfectly possible to maintain water temperatures around 25 C. I would not however attempt this out doors. Some kind of building is essential. A poly tunnel or green house would be well worth the investment, even if additional heating was not installed. The systems I have built and managed have all been built in a mushroom poly tunnel around 1,000 sq. ft. in area. This is essentially a poly tunnel with 150mm of glassfibre insulation sandwiched between two layers of polythene. The heat loss was so low that a temperature of 25 C could be maintained for 9 – 10 months of the year just from the heat of a 0.75kW. water pump.
The community of microorganisms living within the biofilters will also have their own preferred temperatures. Again their metabolism, and hence ability to breakdown ammonia, will be dependent, partly at least, upon water temperature. Fortunately they have similar optima to the more popular choices of warm water fish for aquaponic systems. Nitrosomas is thought to be most active at 28 C. Activity falls off steadily as the temperature drops. In fact, below 5C. nitrification grinds to a halt and declines sharply over 42 C.
Temperature is so important that anything we do to help elevate water temperatures will promote more rapid fish growth. There have been many ingenious schemes to help achieve this including ground source heat pumps, wood pulp burners and even tapping into the heat generated from compost heaps. h