It is hard to give any general rules as to the growth rate of tilapia. Different strains grow at different pace in different environments. This means that a strain that is fast growing in one location can be slower in others. The growth rate is affected by a number of different factors that works together to decide the growth rate of tilapia, such as water quality, water temperature, the health of the fish, food supply, and oxygen levels. The amount and type of food you give your tilapia will have a dramatic effect on their growth rate – it is actually one of the most important factors – but the other factors will also have a large impact overall. The type of farming you use can for instance affect growth rate significantly and so can stocking density.
Different strains of tilapia will, as earlier mentioned, grow at different rates in different environments. Some strains are for instance fast growing in brackish water but not very good choices in pure freshwater. It is therefore very important to choose a good strain for your particular fish farm if you want to optimize growth. Don’t get fooled by advertising promoting super fast growing strains; they will only grow fast if your farm suits them. If it doesn’t, you will be better of getting another strain, one that is more suitable for your fish farm.
In addition to factors mentioned above, the growth rate of tilapia is also affected by whether you use mono or mixed sex cultures in your farm. If sexually mature male and female tilapia is kept together in a tilapia farm they will start spawning if the temperature is high enough. Tilapia is a very prolific fish and they produce a lot of offspring. These offspring compete with the parents for food and living space. This will cause all the fish to grow slower and might even cause stunting in the fish. This is a problem in a commercial tilapia farm for obvious reasons. A number of different methods have been concocted to combat this problem of which three is commonly used:
Raising mono-sex tilapia
This involves buying all (almost) male fingerlings and using them in the farm. It is also possible to produce (almost) all male batches yourself. You can read more about this in the article about breeding mono-sex tilapia. The reason mainly tilapia males are used for mono-sex culture is that they have a higher growth rate and a larger max size than females.
Raising tilapia in cages or tanks
The second method is to raise mix sex fish in cages or tanks that disrupts their breeding and thereby avoid this trouble.
The third commonly used method is to harvest the fish before or shortly afterward they reach sexual maturity. This method means that you can not produce as large tilapia fish as you can with the other methods.
I will when discussing growth rate in mixed-sex cultures focus on cultures that are being harvested before the fish reach sexual maturity as this is a much more common practice than tank and cage breeding. It is important to choose the right species when using this method. Blue tilapia (Oreochromis aureus), Nile tilapia (Oreochromis niloticus) and most hybrids produced from these species are good choices as they will reach a marketable size before reaching sexual maturity. Mozambique tilapia (Oreochromis mossambicus) and Wami tilapia (Oreochromis urolepis hornorum) should be avoided as they start spawning at a very small size.
The short growth period in tilapia that is being harvested before they reach sexual maturity is short and the growth rate is therefore very important to make it commercial viable to breed tilapia this way. Due to this reason it is very important to avoid to dense stocking. If you chose the right species or hybrids and provide a good environment it is possible to get the fish to reach a marketable size in 4-5 months. In temperate regions, it is possible to get tilapia ready for harvest by autumn.
When using a 4-5 months growth period (sexual maturity) it is common to use 1 month old fry and stock 2,000-6,000 per acre. If you use a stocking density of 4,000 fry per acre, you can expect the average size of each tilapia to be 0.5 pounds (220 grams) by harvesting time, provided that you have supplemented their diet with protein rich food.
Growth rate for mono-sex cultures (all male)
If you wish to use mono-sex cultures you will have to buy or produce all male fry (males grows faster and bigger than females). All male fry can be produced through hormone treatment or hybridization. There is also a new method called YY male technology which is being developed but this method is not ready for use yet. Hormone treated fish are not allowed to be sold on certain markets world wide and there might be restrictions on using hormones in your area. You should therefore always research this carefully before deciding to get hormone treated tilapia.
N.B! So called all male tilapia batches are usually not 100% male. There is a margin of error, usually around a few percent. This can for instance be caused by foreign genetic material being present in the parent fish used for hybridization. To get really large and fast growing tilapia there should be no more then 4% females in the culture.
Most mono-sex cultures are densely stocked. This reduces the growth rate in each individual tilapia but increases the overall yield per acre. Densely stocked cultures are however more susceptible to disease and it is therefore important to carefully maintain the water quality. Less then perfect water quality can easily cause disease and reduce growth rate in tilapia.
The typical mono-sex tilapia stocking density varies between 4,000 to over 20,000 fishes per acre. A higher number requires more work to maintain and extra aeration. If you’re not able to provide this you should choose a lower stocking density. If the fish are provide with a good environment, good water quality and an adequate supply of nutrition it is possible to grow 50 gram fingerlings to become 500 gram fishes within 6 months (180 days) even without supplemental aeration if the stocking rate is 4,000/acre. The above example means an average growth rate of 2.5 grams a day and a yield of 2.2 metric ton/acre. With aeration and denser stocking you will see a little slower growth rate in each fish but a higher overall yield. A stocking rate of 8,000/acre (for a total yield of yield of 4.4 tons/acre) will for instance require night time aeration. Aeration might also on occasions be needed during the day. The average growth rate in such a pond is 1.5-2.0 grams/day and it will take 200 days or more to get 500 gram tilapia (4.4 metric tons/acre).
A pond with 4000 fish will yield 2.2 metric ton in 180 days or 12.2 kg (27 pounds) a day. A pond with 8000 tilapia will give 4.4 metric ton in about 200 days, i.e. 22 kg (49 pounds) a day. As you can see the overall yield per day is much larger with a higher stocking density and will be so even if it takes more than 200 days for the fish to reach the desired size. Higher stocking rates can give even higher yields but will require constant aeration and careful water monitoring.