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Tank Thermal Performance Implications in Aquaculture Yields

Aquaculture Fish

The majority of fish species require a relatively narrow range of water temperature and particularly low-temperature fluctuations to survive and thrive.


Due to the inability to regulate their body temperature like mammals, fish are dependent on the temperature of the water within their habitat. While they are tolerant to a range of temperatures, daily temperature changes if not controlled optimally can lead to increased stress, decreased disease resistance, and decreased growth and yields.

Species must therefore be chosen carefully to match the local climate and natural water temperatures with the tolerable extremes of the species. Ideally, the natural water temperatures would always be within the optimal growth temperature range of the species being reared.

Table 1-1. shows the temperature ranges that various species require to survive as well as thrive. If we look at Trout, for example, has a tolerable extreme of 0 °C to 32 °C with an optimal growth temperature of 17 °C. The range of water temperature that trout can tolerate, a 32˚C spread, is quite large when comparing them to other species on the list. Freshwater prawns, for example, can handle tolerable extremes of 24- 32˚C (8˚C range).

Lund, Aquaculture: Heat Loss from a Pond 1996
Species, temperature tolerance, and optimal growth (Lund, Aquaculture: Heat Loss From a Pond, 1996)


In the case example of a salmon, trout, or striped bass rearing facility in any climate where daytime highs reach 30° C will incur substantial cooling costs. Conversely colder winter temperatures will require extensive heating of water and air added to the tanks. Adding insulated thermal mass to the tank not only regulates these temperatures but curbs daytime high and low energy costs significantly.

Spea's Hatchery
Dan Speas Fish Hatchery, Wyoming


Octaform combines concrete’s modest insulative properties and very substantial thermal mass with EPS foam insulation.

R-Values, tell the story of how quickly temperatures will equalize from one side to the other of a given material. The challenge is that many of these materials are evaluated in the context of an overall structure that has varying levels of thermal bridging. It does not account at all for the value of combining the material of high thermal mass, relatively low R or U-values, and somewhat heat-conductive inside a very low thermally bridged structure and insulated by a high R-value material like EPS foam.

When you increase the thermal mass of water and insulate externally a few things can happen:

  1. The effective R-value overall goes up and the net performance is much higher than the calculated R or U-Value.
  2. It takes a lot longer for the contained fluid to change temperature which means less risk of temperature variability for fish.
  3. The additional thermal mass may even mean that the number of days or hours where cooling or heating equipment is used is significantly less – daytime highs and lows may be absorbed by the additional mass.
  4. If new water needs to be added to a system, more can be added without requiring pre-heating or pre-cooling.
  5. Similar scenarios have been proven with hog barns in the University of Manitoba study which showed after introducing cold air (-20C) to the barn, it returned to temperature much more quickly after doors closed and required 8% less cycle time on the HVAC system to do so.


Octaform combines low thermal bridging and thermal mass of concrete inside insulation to improve performance and decrease energy costs. Fish are not the only species, Octaform has been building barns for hog rearing for over 20 years and has been studied extensively due to thermal performance. Hogs exposed to temperatures over 25 degrees celsius experience significant heat stress, increased cortisol, and metabolic rate leading to decreased growth and increased disease. Octaform has been preferred to improve hog performance and decrease heating and cooling costs for decades.

Moving to much smaller organisms, thermophilic bacteria also need a very narrow band of temperature to perform optimally in their role in thermophilic digesters. Octaform’s combined thermal performance from ultra-low thermal bridging and additional thermal mass of the concrete means more performance, throughput, and profits. Owners consistently report more net yields than expected from their digesters’ designed expectations.

Smolt Tanks, Westfjords, Iceland