Richard bray

Fish Selection & Culture
The fish in your system will provide the nutrients for your plants. This dynamic relationship between fish and plants can be difficult to maintain, which is why it’s important to choose fish that are appropriate for your system, climate, and crop selection.
Foto-Sabine/Shutterstockcom
Any freshwater fish that does’ well in tank culture is a possible candidate for an aquaponic system. Fish must be stocked to a certain
58
density ratio to achieve the right proportion of nutrients in the water, so any fish you choose must be able to thrive in close quarters.
There are two different ways to determine how much fish you need in your system.
If your goal is to maximize fish growth for harvest, you need a lower stocking density to give them space to grow to a full size. In general, this means using a 1:10 ratio of lib of fish weight to 10 gallons of tank water. Calculate the fish weight based on the average, mature weight of the fish.
If your goal is to maximize nutrient content in the water, you need a higher stocking density to create more waste for the system. This can range from 1:10-2:10 pounds of fish to gallons of water, depending on how well the fish can tolerate higher stocking densities.
However, stocking density is only part of the equation. Higher volumes of fish will only result in higher volumes of nutrients if the fish are fed the correct amount of food, and feeding rates depend on the age of the fish. Young fish can eat up to 30% of their body weight in food each day, and produce significantly more ammonia than adult fish. Adult fish eat much less, about 3% of their body weight, and produce less ammonia per pound of body weight.
The amount offish your system can support will also depend on your grow bed area. For every lib of fish, you need 50 sq’ of biological filter surface area. This includes the surface area of your grow bed, grow media, filters, and sump tank.
The surface area of grow media and biological filter media is measured in a sq' per cu' ratio. For each cubic foot of media, imagine the media
59
unzipped and flattened, and then measuring the square footage of the media.