cold2          The dirty weather, rain, wind and lightning that blows through before a surprise early-season cold front makes it difficult to prepare the fish house.  The plastic sheeting that serves as both roof and heat generator is nothing less than a giant sail when spread out in the wind.  Still, spread out it must be, the length of the fish house, and secured on one side.  Line are tied at one end at spaced intervals to the plastic and weighted at the other end so that they may be thrown over the arched roof to the ground on the other side.  Each worker takes a line and the group pulls en masse to slide the plastic across the top and over to be tightly secured on the other side.  The cathedral openings at either end must also be closed in with plastic sheeting in order for the green house effect of captured infrared sun light waves to be effective.  Once closed in, the house is a haven for the fish, generating 10-15 degree warmer temperatures inside during the day than outside the fish house walls.  A 70 degree day is still a warm 85, for example, within the fish house.  Over the length of the day, this extra heat is infused into the water especially where the return water is spraying out through the air, oxygenating itself as well as picking up the ambient heat and mixing both heat and oxygen into the raceway water.  This stored heat is essential for the evening during which the green house effect, without the aid of the sun, is negated.  However, the plastic still works to keep the wind chill off the raceway water and the water, which holds its heat better than air, stays warm for the night, especially encased as the raceway is by earthen walls which hold heat even longer than water.  Thus the fish, who are as is commonly called cold-blooded, or ectotherms, are helped to keep their body temperatures higher and their metabolisms and growth rates productive for the farmer.

An additional low-cost method of aiding the fish to keep warm is to run the return water through black pipes or hoses along the roof of the fish house.  The black absorbs the sun’s energy and transmits it directly into the water as it passes through.  This can add additional energy to the growth potential during cold spells.

It is often the case that the first night of a cold front is warmer than the second.  This is a result of heat reflecting off the clouds that remain behind after the storm front passes through.  Once that cloud cover has cleared on the second night, the temperatures can drop dramatically.  In the worst case scenarios, it may be advantageous to have an artificial means of heating the greenhouse at night at hand.  Obviously, the open fire method which grove farmers employ to fight frost from their fruit is out of the question in a closed environment.  But a few dependable space heater placed within the fish house on the coldest of nights would be worth the energy cost to keep the fish from stunting in a particularly long and chilly snap. This said, it must always be remembered that electricity and water are a volatile mix and no snake is quicker or more lethal than the sparking head of a wet coiled wire.

The ambient temperature is integral to ectotherms.  Tilapia mate only when temperatures are above 20 C or 68 F though only the most robust participate in cool water.  They grow at maximum efficiency above 29 C or 80 F.  Below 18 C or 60 F they do not grow at all despite abundant oxygen and food and good water quality.  Below 8 C or 47 F mortality occurs on a severe scale.

Water quality is also intricately related to temperature.  Hardness and alkalinity, both factors which affect fish growth and overall stress levels fluctuate with temperature.  Oxygen, as is true of all gases, escapes water rapidly as temperatures rise and remains more soluble as temperatures drop. Remember, as Doctor D always says, the only thing that without a doubt will kill a tilapia is lack of oxygen.  They will find ways to stay alive on ice or in hot water. Even out of water in at least a damp place they can survive hours and perk right back up once placed in water again.  They are disease resistant due to their body slime, their tolerance of salt in the water, and especially their lowest of all fishes stomach acid which acts as a near impenetrable barrier to bacteria.  But cut off the oxygen in the water and they are dead.  In the summer when water temperatures are ideal within the raceway fish house, it is imperative that the farmer keeps a close watch on oxygen levels to avoid low-oxygen stress or die-off. Generally, cold water is easier to manage, but it is simply a waste of money to feed and provide oxygen to fish whose metabolism will not permit growth.  Given all of the above, it is clear that as the temperature of the water goes, so goes the farmer’s fish crop. Dealing with the cold front will earn money back.