High environmental demands
Rainbow trout doesn't need as cold and oxygen-rich water than Finnish Brown trout, but still it's clearly fish of cold waters. It doesn't tolerate acidic water: breeding don't success under pH 6,2.
Food taking
Rainbow trout's menu is quite similar to Brown trout. When young it eats larvae, small crustaceans and also insects from the surface. It becomes predator when reaches 35-40 cm, later than Brown trout.
Spawning
Pic: Mike Cline.
In Finland Rainbow trout spawn yearly in Spring, in April-May. For spawning it demands streaming water with suitable gritty bottom and clean, oxygen-rich water. It is possible that Rainbow trout's spawning is successful in Finland and chances get better as climate gets warmer. Single successful spawnings has reported, but no reproductive population is risen.
Size and significance
It's found that Rainbow trouts are not growing much after released to natural waters. Typical catch is 0,5 - 3 kg. From the sea has caught some 4 - 6 kg fishes.
Rainbow trouts are put on angling -ponds and cascading angling places to make chances to get fish higher. It has become significant resource for fisheries industry as article of aquaculture. It's been grown yearly to portion sizes 15 million kilos.
Sources:- Koli, Lauri, Suomen kalat
- FGFRI's stats (In Finnish)
- Fish records (In Finnish)