Starting from the basics of designing a fish farm, lets take a look at how we arrive as some of the first steps to design criteria which will lead us into in-depth calculations for production. First we have to start with how much and what species we want to grow each year and drill down deeper into the design process. Before we start it is important to recognize the results we gain are only as good at the data we use. It is important to use as many data point as possible and don’t underestimate the value of experience when developing your farms bio-metrics. Understand we have to make very large assumptions about what might happen on the farm. Once we get to the end results review them to be sure they meet practical experience. In this scenario we have chosen Tilapia and we want to grow at least 20 ton (20,000 kg) per year. The challenge when starting to work on this design is knowing how often, what quantity and size of our fingerlings as these will change our production planing for the farm. We are assuming we can get (or hatch our own) fingerlings all year round for staged production. We have determined that we can get in fingerlings at 0.5 grams every five weeks in sufficient quantities to support our production goals. The five weeks is an important number as it gives us close to 2,000 kg per cycle (5 weeks) in which we can harvest approximately 400 kg per week should our market require that. We will look a little closer into how this 5 weeks of harvesting affects our overall biomass especially if we are not going to harvest the 2,000 kg in one go after they have reached the required size of 500 grams. Setting a fixed target size for market is very important, but often it will vary because not all fish grow at the very same rate. This could be due to genetics, but in most cases it is feed quality and management that provides you will a severely varied weight result in the fish. Often we will assume 20% will be “bulls” or fast growers, 60% will be of the average stock and if you are unlucky 20% will be runts. We will talk more about culling later. Holding stock over a little longer happens quite often in a farm so we need to plan for that extra biomass in the system or our bio-filtration and pumping will not keep up with the increase in load and risk the entire operation. This is a very simple, yet devastating mistake made by inexperienced designers. The harvest cycles and number are relatively simple. However the length of the fish is a formula derived from the weight. While it may appear not gravely important and often it is not, however it is a measure that we use to determine if the condition of the fish is poor or great and is done during operations. What is does tell us or let check is the physical size of the fish suitable to our density which we cover in our third part. The number of fish for final harvest is an important number we work backward to account for production mortality or intentional culling. It is not a design criteria but an operational production number that will help determine what you will send to market. So if we are making arrangements to send a minimum of 3846 fish at 500 grams to market each year, we need to be sure our mortality do are not excessive, leaving us short of supply. Not a good outcome with your customers. It is very easy to fall into the trap that the date we put in the assumed bio-metrics will happen on the farm. We can only provide a best case scenario and adjust our planning to suit changing conditions in the farm. Ignoring this will see failure, not immediate but imminent. You can see above the change in production just by holding over the last stage of growth an additional 5 weeks. We went from 500 gram fish to 740 gram fish and our production gained 9,500 kg per year. This might look like a great thing but we are designing a 20 ton farm not a 30 ton farm. A result like this not accounted for in the design, will kill all of your crop. As a general rule of thumb we may design an buffer (or stuff up factor) of 30% built into the bio-filtration and the pumping systems. However, if your budget is very tight, it is important to identify if you are going to carry stock over any longer than planed. This will happen from time to time with a tank or two if unless you have fixed supply contracts with your buyers. If not, then plan for the worst where some weeks they may take 200 kg others 400 kg and sometimes they may want 600 kg. Be absolutely certain what your market will bare. While this stage is very simple, the design process will become exceedingly complex, so we are breaking it up into very small chunks to chew on. Next we will cover the culture conditions which also play a role in our overall production….
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