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20 Ton Tilapia Farm – Part 2 – Conditions

We now progress with out 20 ton Tilapia farm design and look a little closer at some of the conditions in the culture that will effect the growth of your fish.  Such as temperature, their condition, mortality/ culling rates and density capacity by formula.  Changes in these will effect the rate of growth and the production time for the fish.  While we are still in overview stages, it is important to understand how these will effect the outcome of your farm design. As fish are a poikilotherm, the temperature of their body changes with the temperature of the culture water and there in effects their growth rate.  In other words, they don’t use energy, like we do (warm blooded) to regulate body temperature for metabolism but rely on us to provide the right conditions for their ideal growth.  We understand that all fish have a specific “ideal growth” temperature range and for our fish, Tilapia it is 28 to 30 degrees Celsius or 82 to 86 degrees Fahrenheit.  We will avoid change back an forth between metric and imperial throughout this series to make it easier on me and not to confuse. As we have stated a range between 28 and 30 it is important to understand how that effects your fish growth and ultimately the production outcome.  As the temperature increases, also the pressure or loading on the life support systems also increases so we need to find a balance between ideal growth, that is financially viable over the growth period and increasing capital and operational expenses with excess temperatures.  Remember as the temperature goes up, so does the cost of operations. If you are in a cooler climate, you will want to consider the energy required to maintain the chosen culture temperature and the cost of providing such against any additional growth you may achieve. In the above example we have increased the culture temperature 1 degree from 29 to 30.  Note the change in growth per month and the saving of 4 weeks in production.  However what does it cost? Water Heating Sidebar:  The costs associated with heating a large volume of water is a consideration when selecting the control temperature of the culture unit.  Because some fish have a few degrees between in their optimum growth range, we need to consider the cost of changes, even if it is 2 degrees as exampled below.       As you can see from our simple calculations above changing the heating degrees by 2 degrees Celsius adds nearly $6000 per year to the overall cost, but more important it increases our cost of production by nearly 30 cents per kg.  This may seem insignificant but you have to weigh that cost against the increase growth rate achieved by the increase in temperature and is the capital (approximately $30,000 for a gas heater) or the smaller system justifiable. The condition factor varies significantly from species to species with some having very little information relating to their condition.  The condition of the fish is determined by the length and the weight.  A high number indicates your fish may be too fat and conversely a low number indicates the fish may be too thin.  Often when growing fish you will record both the length and weight of the fish to determine if your fish are within acceptable ranges.  This condition can also reflect their general health and will indicate the feed may be wrong, feeding too much and even the tank velocities are not correct.  Eg: even if the water quality is good a fat fish may indicate the culture tank velocity is too slow. While you may think fat fish are a good thing (like putting salt in cattle water troughs before sale….) when purchased the meat recovery will be lower and the chef may notice this.  If they are discarding too much of the fish because it is laying down fat, they may choose a leaner fish instead of yours.  If they are too thin, their presentation will be poor.  It is a bit like Goldie Locks… too fat, too thin, just right.  This takes practice. If the condition of the fish is set too high in your design, you will shorten the production time which will give you false hope and your life support systems will not be adequately designed and have a high chance of failure.  There is some literature about condition factors for a few species of fish.  When in doubt lean to the number that ensures your production cycle is set up within practical reason. The density formula is not about what culture density you will grow the fish at but it will help (later) check the density you have chosen is within the physical limits of the fish.  In other words allowing for enough space, regardless of life support for the species you have chosen.  The resulting density will generally be quite high.  These high density numbers are not a concern but I would avoid growing at them unless you or your production staff are suitably skill in the husbandry of the fish.  This will be discussed a little later on in this series. The mortality and number of fish stocked again is calculated in our next session and is the result of estimating the losses, intentional or unintentional, to be sure you have the desired production every year.  This is essential for predicting the amount of fingerlings you will bring in each cohort.  However those mortality are not accounted for in the design. To clarify the mortality at this point.  If you stock 5000 fish and by chance everyone of them survive, but you have designed only for the number you want to which reaches your production goals, your life support systems will be severely lacking.  This is a very basic trap I have seen many people fall into.  They design a system and estimate they may lose 20 % of them and find out they only lose 1% and they system is way overstocked.  Unfortunately if there is lack in the design it is incredibly hard to fix when you have a system at biomass and often it is too late or impossible to fix.   Be careful with assumed losses. That covers our basic “desires” for our farm production.  Next we will start to get down into the nitty gritty of the design and look at production staging.  As we dwell deeper, a greater understanding will come….

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