by Sunny Datko
In aquaponics, the nutrient-rich water that results from raising fish provides a source of natural fertilizer for the growing plants. As the plants consume the nutrients, they help to purify the water that the fish live in. A natural microbial process keeps both the fish and plants healthy. This creates a sustainable ecosystem where both plants and fish can thrive. In this symbiotic relationship, fish waste provides a food source for growing the plants; and the plants supply a natural filter for fish.
How Does Aquaponics Work?
In an aquaponic system, beneficial bacteria convert the fish wastes into nutrients that the plants can use. More than 50% of the waste produced by fish is in the form of ammonia, secreted through the gills and in the urine. In sufficient quantities ammonia is toxic to plants and fish. Nitrifying bacteria, which naturally live in the soil, water and air, convert ammonia first to nitrite and then to nitrate which plants consume. In your aquaponic system the nitrifying bacteria will thrive in the gravel in the fish tanks and in the growing medium in the grow bed. The plants readily uptake the nitrate in the water, and by consuming it they help to keep the water quality safe for the fish.
What Type of Fish Can You Raise?
Fish are the powerhouse of an aquaponics system, they provide the nutrients for the plants and if your growing edible fish, and they provide protein for yourself. Keeping fish may be a little daunting to some, especially those without any prior experience, however don’t be discouraged. Keeping fish in an aquaponic system is simpler than keeping aquarium fish, so long as you follow simple guidelines then it can be extremely simple.
For starters, we recommend using one or more of the following species of fish:
- Tilapia – The second most cultured fish in the world, and extremely popular in aquaponics systems. They are an ideal species for aquaponics for many reasons. They are easy to breed, fast growing, withstand very poor water conditions, consume an omnivorous diet and are good to eat.
- Koi – Another species of carp, Koi are very common within many Asian communities and are often found in large ornamental ponds. For those who love Koi, an aquaponic system is a great proposition for stocking the fish.
- Trout – Trout are a great fish for aquaponic systems where water temperatures are a little cooler. Trout prefer water temperatures between 10°C and 20°C. They have extremely fast growth rates and excellent food conversion ratios.
- Other Species – Other aquatic animals that can be incorporated into an aquaponic system are fresh water mussels, fresh water prawns, and fresh water crayfish. Mussels & crustaceans also make nice additions to an aquaponic system.
What Should You Feed Your Fish?
The quality of feed you select not only determines the health of your fish, but also considerably affects the health of your plants. There are typically two types of fish feed sold in the U.S. – omnivorous and carnivorous – and they vary mostly in their protein content. Within these types, you can select feed according to the stage of growth your fish are in. Again, the formulation difference will largely be the amount of protein in the feed, although you will also notice a difference in pellet size. Not surprisingly, as the fish get older, the size of the feed pellets gets larger.
Fish feed is comprised of proteins, fats, minerals, carbohydrates, and other nutrients that a fish in the wild would have in their normal diet, but that they cannot get in what is essentially a wet desert in captivity. The sources for these nutrients are usually from fishmeal, corn, soy, and other animal byproducts. All fish feed, especially brands that use more natural ingredients and fewer preservatives, have a limited shelf life and are best stored in a cool, dry location.
Fish can tolerate a wide range of feeding schedules very well. They actually adjust their metabolism to match food availability. However, the best fish feeding rule of thumb is only feed your fish as much as they will eat within five minutes. After five minutes, remove the remaining food from the tank with a fish net. Soon, you will be able to judge just how much food to toss in, depending on your fish’s behavior at that moment, and you will no longer need to wait five minutes to see how much they eat.