- Associated Press - Monday, September 25, 2017

SPEARFISH, S.D. (AP) - Fisheries crews at McNenny State Fish Hatchery may have found a cheap and simple tool to significantly increase the size of the fish they raise: A child’s toy.

Through time, there have been concerns on how fish were raised in hatchery settings in relation to post-stocking survivability or how they behave after being released into the wild, said Mike Barnes, the manager of the hatchery. So hatchery personnel added structure such as brush piles or even small trees, the Black Hills Pioneer reported . Barnes said his crews even tried introducing concrete blocks into the tanks.

“The problem with all that is that it interferes with fish production,” Barnes said. “Circular tanks are all self-cleaning. If you introduce things directly into the bottom of the tank, it just destroys that. Now you are having to spend a lot more time cleaning, and you can have disease issues.”

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One day as the McNenny team was brainstorming ideas, someone asked about suspending something in the tanks.

The hatchery had aluminum rods left over from a previous project, so the crew threaded the end of the rods, placed a nut of the end, and lowered the 20-inch rods into the tank, clustered together. The rods were suspended about nine inches from the bottom.

“The initial thing was to just see how they modified the self-cleaning tanks,” Barnes said. “Would they be suitable in a hatchery setting?”

The employees set up the study using the rods in some tanks, the experimental tanks; and not altering other tanks, the control tanks. The tanks were stocked with the same number of fry, baby fish, and fed at the same rate.

“At the end of three or four months, we were just shocked. Our tanks with just covers had something like 120 pounds of fish, which is what we expected. But the ones with the rods had 150-160 pounds.”

The exact reason for the significant increase in not yet known. Barnes suspects that there was slack water created from the rods being suspended in the tanks. This would provide a small area of refuge for the fish. Perhaps the rods altered the water flow, creating a more even water quality in the tanks, and perhaps the fish are less stressed and realize better growth because there is structure added to the tanks even though that structure was aluminum rods.

So in spirit of the McNenny mantra, the crews took their experiment to the next step.

A study from the West Coast indicated that there may have been a positive response in salmon, close cousins to the rainbow trout raised at the hatchery, when color was added to their environment; however, those results were purely speculative, Barnes said.

A former hatchery employee, Jeremy Kientz, went to Walmart with his state credit card to purchase a couple of bags of plastic play balls, similar to those found in play pits. Kientz, a new employee at the time, was in his hatchery uniform but could not get his state-issued credit card to work.

Barnes said a man behind Kientz in line asked what the balls were for. Kientz told him, and the man said, “That’s cool,” and paid for the balls with his own credit card.

Kientz did not catch the man’s name.

“I’d like to very much thank the man,” Barnes said. “Those balls elevated the game to the next level.”

The hatchery crews suspended the balls similarly to the aluminum rods.

“At the end of the rearing period as we expected; we got 120 pounds in a covered tank, 150-160 pounds in the tanks with the 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,” Barnes said.

The cost per tank to improve the 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 addition prevented the self-cleaning function of the tanks.

Barnes said studies will continue.


Information from: Black Hills Pioneer, https://www.bhpioneer.com

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