The variety of species able to be kept in aquaponics is very wide. In this article we will see how to raise trouts and why they are such an interesting species to raise.
Trouts have been domesticated and raised in captivity for 150 years for the following reasons:
Very fast growing fish
A trout raised in good conditions can reach the commercial “portion size” of 250g in 9 month and reach 500g in a year. It is considered as a fast growing fish comparing to other species. If kept long enough they will reach 5kg in 4 years but if you are growing them to eat them, it’s probably better to harvest them between 1 to 2 year old. The old fish grow slower and become more fragile and more likely to fall sick.
The oxygen consumption of trout is higher than the average fish. The comfortable limit is 7mg/l but in practice they can survive in lower concentration depending on the temperature and the stress level. I have personally seen trouts stocked at very low density surviving in 3mg/l but it’s not recommended.
Trouts are known to be “cold water fish” which mean that they are adapted to colder temperature than other tropical fish. Rainbow trouts hardly survive a temperature above 23C. This fish is therefore not adapted to tropical country or country where the temperature raise too high.
As all the other fish, their growths is still dependent on the water temperature. The closer the temperature will be to their optimum and the faster the growth.
Ammonia, Nitrite, Nitrate
Trouts are sensitive to toxic substances and require a clean water. Ammonia and nitrite concentration must be kept under 0.5ppm. Depending on the pH and the water temperature, the ammonia concentration can become lethal around 0.8ppm
Nitrate should be kept under 50ppm. If you see the nitrate raising simply renew some water of your aquaponics system and use it to water your classic garden.
The trout maturation occurs at 1 year for the males and 2 years for the females. Once this point reached the fish will use a significant quantity of energy to produce gametes (sperm and oocytes). The fish growth will therefore been slowed down. If you produce trout in the aim to eat them it is more productive to harvest them before maturation. It is important to understand that domestic rainbow trouts will not spawn naturally in your tank and you will not be able to reproduce them.
The trout fingerlings bought from the classic trout hatcheries are 100% females, see this video for more explanation: maximise your fish growth (https://youtu.be/XJSBTq4_yts) . If you aim to grow large trout (over 2 years) you will be able to “strip” the fish in order to empty the eggs from the trout belly. You can then consume the “trout caviar” which is a real delicatessen. Another option if you want to grow large trouts is to grow triploids trouts, see with your fingerlings supplier.
Rainbow trouts are a domesticated fish species. Their diet has been scientifically studied and the fish food supplier developed dry pellets very well adapted to their needs. Adapt the size of the pallet to the size of the fish. Be aware that the colour of the trout flesh size will be dependent on the fish food used, see those videos: How to feed your fish (https://youtu.be/eLI4zCEhdOs), fish flesh colour (https://youtu.be/tmj4wsDMNto). The distribution must be even and all fish must have access to the same quantity of food. If some fish are left behind, the size difference will increase and the small fish growth will be very slow.
Trouts are widely grown around the planet (not in tropical country) because of the quality of their flesh. They offer a nice soft texture with a fantastic aroma. This fish can simply be grilled with butter, garlic and parsley. You don’t even have to scale the fish, if you grill it skin side on the pan, the scales will become very crispy and excellent J. Most of the omega 3 and other interesting poly unsaturated fat are stored in the skin of the fish so it’s always interesting to consume it.
Trouts are natural predators and will eat anything that can fit in their mouth. I recommend to keep them in group of 10 or more (depending on your fish tank volume). When kept in very low number their territorial behaviour will be developed and one of them will chase the others. They will become stressed and weak. Generally the weakest ones will not grow well and may fall sick and die. It is therefore to keep the fish in “significant” number.
There is lot of research around trout disease, like most other fish species, they are sensitive to virus, bacteria and parasites. Trouts can get several virus disease mostly when the water is cold. The bacteria infection such as Furonculosa and Yersinia happen when the water is slightly warmer. In aquaculture the trouts are sometimes vaccinated against those to bacterial disease and when the fish get sick, antibiotics are used. In aquaponics we use a different approach and focus on keeping the fish in low density and therefore minimize the chances to stress the fish and catch any disease. Parasites such as costia and fungus are also very present on intensive farming. They are often managed thanks to chemicals such as Formaldehyde and potassium permanganate. In aquaponics we will use salt and if we need to use other products we will use the bath technique, see this video (https://youtu.be/0eA4UiuOs70)
Trouts have been selected for generations and a specific breed has been isolated with a golden pattern. The golden trouts present the same specificities as the classic rainbow trouts but the colour is amazingly yellow/orange. They are very much appreciated for ponds but are not very well adapted to be grown in dams as they are very easily detected by their predators (birds). It’s a very nice fish to grow in aquaponics as they look great and taste fantastic!
Where to find little trouts (trout fingerlings)
To stock your fish tank you can call your local fish farms. They should be able to offer little trouts for an affordable price. You can take this opportunity to get some fish food. When you transport the fish make sure to not stress them and the quantity of fish per volume of water is reasonable. Call the farm the day before, the fish shouldn’t be fed before transportation.
Ps: If your water temperature is raising too high during summer only, you may still be able to grow trouts for only 9 month of the year. The fish will be big enough to be harvested before summer.
Density: up to 100kg/m3 in aquaculture but only 20kg/m3 in Aquaponics
Conclusion: Trouts are a very interesting species of fish to grow in aquaponics and I recommend it to everyone.
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