Last year they installed vertically oriented aluminum rods to provide structurally complex environments in their trout tanks. This year they added small colored balls to the mix. Both projects yielded positive results.
In the project last year (Hatchery International, Sept/Oct, 2016) Mike Barnes and his team studied the growth and condition of juvenile rainbow trout reared in circular tanks containing nine vertically oriented round aluminum rods (structurally complex) compared with that of trout reared in tanks with no rods (control).
In their latest effort they reportedly included brightly colored plastic balls to provide additional complexity to the environment in the rearing tanks. At the end of the rearing period, Barnes told the Black Hills Pioneer they got better results than ever.
“As expected; we got 120 pounds in a covered tank, 150-160 pounds in the tanks with aluminum rods, but the tanks with the balls, for the first time in my 28 years out here, we had tanks with over 200 pounds of fish, which is totally unprecedented,” he told the newspaper.
The potential impact of structural complexity on the rearing performance of juvenile fish has largely been ignored, but Barnes’ team has looked at whether it would benefit trout during the early lifecycle stage in the same way that complexity has shown to improve post-stocking survival.
What makes the McNenny Hatchery research unique, he explained in the 2016 Hatchery International article, is that it focuses purely on the hatchery rearing aspects of a structure that didn't interfere with normal hatchery practices (i.e. no more work for hatchery staff).
With the recent plastic ball study Barnes said they found a relatively inexpensive way to improve trout hatchery production which less man hours for his team.
The cost per tank to improve fish growth: about $2 or $3, he said.
The team added even more balls to the tanks and still saw good levels of growth, but the additional balls interfered with the self-cleaning function of the tanks.
Editor’s note: Hatchery International reported on a similar project at Loch Duart’s Sutherland site in Scotland where staff installed coloured balls in the facilities tanks with similar positive results. See Hatchery International July/August 2016.