High fish stocking density poses a significant risk in both aquaculture and aquaponics. Commercial producers, aware of the risk-to-return ratio, refrain from implementing such dense stocking practices. Consequently, it is advisable for home producers to completely steer clear of it due to its lack of profitability.
Online, there is a lot of discussion about achieving a high fish stocking density of 1 fish in 10 liters of water. This density can be achieved in quarantine systems with fingerlings and enough tank space to sort them out. However, without proper filtration, it would be difficult to maintain these fish at high density for an extended period of time.
Newcomers to backyard aquaculture and aquaponics are finding it confusing to determine how many fish they should have in their systems. Additionally, there have been some unclear explanations provided regarding the reasoning behind stocking a specific number of fish.
So how many fish should you have?
The first thing you need to consider is the number of fish you want to cultivate or require. This will vary depending on the number of fish you plan to consume per week and the number of people you are feeding at home. However, if you are aiming for commercial growth, the quantity will be determined by the annual weight of fish you can sell and the cost of production. For illustration purposes, let’s assume a quantity of 50 fish.
After considering the previous point, the next aspect to think about is the desired size of the fish that you intend to grow. For instance, if you prefer consuming fish that are around 500 grams in weight, this is generally regarded as the typical market size for various species called “plate size”. Although there may be variations in size, both smaller and larger, the choice ultimately is yours. However, if your purpose is to cultivate fish for selling, you should determine the size based on the preferences of your customers.
The challenging aspect lies in determining the amount of fish to be stocked in relation to the volume of water. This variable is referred to as the stocking density factor, which can be measured in kg/m3 or lbs/ft3 depending on the geographical location. Converting between these two units is easily achieved through multiplication. To convert lbs/ft3 to kg/m3, multiply by 0.0624, and to convert kg/m3 to lbs/ft3, multiply by 16.02.
If you struggle with math, you can rely on Google for help. If you prefer using lbs per gallon, you should know that there are 7.48051948 US gallons or 6.22883288 Imperial gallons per cubic feet of water. As a general preference, I tend to stick with the metric system.
Avoid high fish stocking density!
Without knowledge of the specific configuration of your system, it is challenging to provide a comprehensive recommendation on density. However, there are three fundamental factors that can enhance fish growth and wellbeing, all of which are connected to the oxygen provision in your fish tank.
- Do you have a minimum fish tank water exchange of 1 to 1.5 timers per hour?
- Do you have adequate aeration either by air stones or water return?
- Do you remove fish solid wastes and uneaten food through the use of simple solids filtration?
- If you have the first one only, good water exchange then 10kg/m3 or 0.63lbs/f3 will be ideal.
- If you have great aeration and water exchange then 15kg/m3 or 0.94lbs/ft3 will work well.
- If you have all three you may be able to achieve 25kg/m3 or 1.56lbs/ft3.
By adding solids filtration, even with basic ones, you will be amazed at how much more productive your system can be.
It is possible to achieve densities above 25kg/m3 if all the necessary requirements are met and there is an enhanced solid filtration system. For beginners, it may be advisable to wait until you have successfully raised some fish and gained a good understanding of your system’s capabilities and limitations before attempting higher densities.
Once you have made your target density selection, determining the required fish tank volume becomes quite straightforward. For the purpose of our example, we will utilize 25kg/m3 or 1.56 lbs/ft3.
How many fish can I grow in an aquaponics system?
If you have a tank that holds less than 50 gallons of water, we suggest putting in 1 inch of fish for every 1 gallon of water. As an illustration, if you have a 10-gallon tank, you can have either 10 fish that are 1 inch in size or 5 fish that are 2 inches in size.
For tanks larger than 50 gallons, it is advisable to have a stocking density of 1 lb of fish for every 5-10 gallons of water or 1-2 fish for every 10 gallons of water. It is important not to exceed a stocking density of 1 pound of fish for every three gallons of water as this can lead to fish stress, fish diseases, and an imbalance in your aquaponic system.
How to work it all out
When working with a tank volume of 1000 liters, it is crucial to consider the actual water volume during operation. Do not mistakenly equate a 1000-liter IBC with a 1000-liter fish tank. If the IBC is modified and the water level remains 100mm below the top (known as freeboard), the actual water content may only be 850 liters.
Handling tank volume
To determine the number of fish to stock in a tank with a water volume of 1000 liters, follow these steps: First, calculate the volume of the tank in cubic meters, which is equivalent to 1m3. Then, multiply the volume by the Density Factor of 25kg/m3. Next, divide the result by the weight of fish at harvest, which is 0.5kg. The final outcome will give you the amount of fish to stock with. In this example, it equals 50 fish.
Working with multiple fish.
In order to calculate the required volume, start by multiplying the quantity of fish (100) with the weight of each fish at harvest (0.5). Next, divide the result by the density factor (25kg/m3). It is recommended to have a minimum of 2m3 or equivalent to 2000 liters. Having a larger volume is preferable.
The number of fish you can stock in your tanks depends on various factors, including environmental conditions, fish size, and other conditions. These factors include bio filtration, which assumes that you have sufficient grow bed space or a specifically designed bio filter that is appropriately sized for your setup.
If you stick to the fundamental rule of 1 fish in 20 liters of water or fewer, you will be able to harvest an abundant amount of fish. By consistently increasing the number of tanks and ensuring optimal conditions for your fish, they will consistently yield a delightful product or meal.
