Now that we have chosen our species, in this example, tilapia let’s see how to produce it.
It stands to reason that we want to produce the product as fast as possible at the lowest possible cost per kg of it produced.
Hence, using the nile tilapia, oreochromis niloticus, which grows at around double the speed of any other tilapia species, makes fundamental sense. The tricky bit is that you will need a permit to farm with nile tilapia as they are considered invasive in South Africa and if you live in Mpumalanga, Limpopo or KZN you will not be issued a permit for reasons as yet unknown to any but the idiots at DEA. This is a battle that has been going on for ten years and will continue for the next ten, so please don’t consider building an aquaculture business in these three provinces based on the nile tilapia. When the situation changes, we’ll update this section accordingly (but we’re not holding our breath). For now the DEA remains ideologically compromised.
Permit issues aside the rate of growth of the nile tilapia is important. It is the first assumption that we will be making and it is an important one. From our growth chart we can see that the nile tilapia can reach 480g at age 210 days.
So this tells us that the fish will spend around 7 months with us before being harvested. However, in looking at the growth chart a little more closely we see that it takes 60 days to reach 8g which is roughly a fingerling size fish. This tells us that if we put fingerlings into the production systems the fish only needs to be there for a further 150 days (this growth chart is included in our paid for plans).
What a BEBTA will tell you is that the growth chart is cast in stone. What we will tell you is that the growth chart in itself is a massive assumption. The numbers reflected on the chart are for tilapia grown in optimum conditions and these optimum conditions are not listed. We happen to know that in fact this chart is better than most because it has been based on measured data across multiple sources, but it is still ONLY AN APPROXIMATION.
This is important. As is often the case with aquaculture, unless you have something else to go on, often you have no choice but to place some reliance to an extent on information provided to you that may be valid only under an entirely arbitrary set of circumstances that bear no resemblance to your own. When you are doing this you need to be extremely careful of the impacts on your business model.
At the risk of harping on the point… A published study carried out by students has shown that they can grow tilapia from 50g to 100 in just 20 days as opposed to the 30 it should take them according to the chart. This is a 1/3rd variation and it has enormous implications – if we could shorten the growing period by 1/3 from 150 days down to 100 we could effectively produce more fish from the same infrastructure. A published paper carries academic credibility and the data in it will be beyond dispute. “Scientists” that just make stuff up tend to publish on the Internet for the gullible. We call them BEBTAs.
You could use this data in your model and build a wonderful looking business plan. However when you build your farm and you can’t hit the targets you are going to start wondering why. You might go back to the paper, and there, in the fine print, you’ll see that the students only managed that growth rate by feeding the fish a new diet of super enhanced glycophaged protein that costs around $100 per kg. Or that they only had 10 fish stocked in a 20kl climate controlled perfect pond with the fish equivalent of personal trainers. Or that they only ran the trials once or twice. Or that the fish were force fed.
The growth chart that we use, or ANY growth chart for that matter is specific to a set of conditions that may or may not be valid to you. Growth rates are super important to we fish farmers just as they are to chicken farmers, but they can only be assumed according to a set of conditions. If you cannot replicate those conditions you cannot expect the same growth performance from your fish (for better or worse).
Factors that affect the growth rates of fish are:
- Dissolved oxygen levels
- Water quality
- Dissolved CO2
- Sex ratio
- Feed quality
- Feeding frequency
- Stocking Density
Changes to any of these can produce substantially different results. Some of these parameters influence each other – the obvious one is the relationship between dissolved oxygen levels and water temperature. The higher the water temperature the lower the dissolved oxygen levels. Ditto stocking density and dissolved oxygen.
Hence a growth chart can only be valid for one particular set of parameters. Change any one of these and the growth rates will be changed. By how much becomes a matter of speculation and best guesses made on available information.
We trust that the point is made. When assuming a growth rate in your spread sheet you need to be extremely careful that it is achievable and that you can provide the same conditions under which the growth chart was formulated to begin with. This can be very difficult – for instance if you are cage farming in a lake your level of control over temperature is nil. If the temperature drops by just 2C, your production can drop by as much as 20% and if you don’t adjust you feed accordingly you’ll lose money there too! What this means is that not only will your production drop but your cost per kg of production in direct costs can increase too.