Cold water fish species, for the purpose of aquaponics, are fish that will continue eating and growing when temperatures dip below 65-70 degrees Fahrenheit. Many of these species require temperatures to stay below the low 80s. In near-freezing winter temperatures, even if their growth slows or stops, many of these fish can survive. Thus, making them ideal to raise in unheated greenhouses within temperate regions. Keep in mind that the plants receiving colder recirculating water will need to be able to withstand the lower temperatures, so plants that usually grow in the spring and fall like lettuce, leafy greens and radishes work better than squash and tomatoes that prefer warmth.

Rainbow Trout

Rainbow trout is the most popular and widely tested of the coldwater aquaponics fish species. They do their best eating and growing in water temperatures between 56 and 68 degrees F, and this is fairly easy to achieve in many climates with a combination of aeration and shade. These fish offer a high relative conversion rate and mature within about 12 to 16 months. Demand for rainbow trout is high due to its flavor and omega fatty acids profile, but you will have to focus on providing a lot of dissolved oxygen and very clean water. Excessive ammonia levels and spikes in dissolved solids can cause trout to suddenly stop growing or die off within a matter of hours.

Sturgeon

Sturgeon is an appealing choice for cold water aquaponics because it can produce a high value roe crop for caviar production in addition to its dressed meat weight. However, you’ll need some ten to twenty- year-old female sturgeon to harvest the roe, so don’t assume that you can turn a quick profit off these fish. There is only limited information currently available about raising sturgeon in an aquaculture system, so there are many unknowns for aquaponics as well. They grow well in temperatures between 60 and 69 degrees F, making them easy to keep in many different regions. Most species require salination, which changes over the life stages of the fish as well. Maintaining a very high dissolved oxygen rate of 90% or above is also required, especially to trigger roe growth in mature females.

Coho Salmon

Farm-raised salmon reduces pressures on wild stock, but many pond and open waterway systems become polluted and produce poor tasting fish. Aquaponics are ideal for producing flavorful and premium coho salmon, which is a species that prefers much cooler temperatures than many other farmed fish species. Because aquaponics systems rely on quality water supplies for crop growth, the fish also benefit from growing in cleaner and healthier water. Salmon are a little tricky because they require water temperatures between 55 and 65 degrees F. You’ll also need to provide more turbulence and water turnover than other coldwater species need, which means more pumps per tank.