It Pays to Keep Yellow Perch Relaxed
Study shows calm perch more profitable for aquaculture

Wave your hand over a tank of rainbow trout, and the long-domesticated fish rush to the surface in frenzied expectation of food. Do the same to a bunch of yellow perch, however, and the skittish fish dive for protection into the far reaches of the tank.

The excitable nature of yellow perch may lie behind the problems they have presented to fish farmers, according to recent work by Sea Grant-supported researcher Jeffrey Malison, a biologist and director of the Aquaculture Program at UW-Madison.

Yellow perch have been tantalizing the aquaculture industry for nearly a decade, Malison says. Their market price has zoomed since wild populations in Lake Michigan crashed about 10 years ago. However, in commercial tanks the fish grow too slowly and survive too poorly to be profitable.

Malison says experiments have shown that stress in other species increases levels of serum cortisol, a hormone that inhibits growth and resistance to disease. Malison suspected yellow perches’ high susceptibility to stress was related to their poor growth and survival in aquaculture, but this had not been demonstrated by research. However, some research had suggested that the wavelength of lighting systems may affect the fishes’ stress levels.

To test these ideas, Malison conducted an experiment with Alex Head, an enterprising undergraduate who, Malison says, "came knocking on my door his freshman year looking for a place to do research." Malison and Head raised groups of fish under low and high levels of disturbance and under three lighting conditions: red (long wavelength), blue (short wavelength), and full-spectrum (all wavelengths) light. For the high-stress group, Head simulated intensive aquaculture conditions in which perch are subject to frequent netting, handling, tank cleaning, and other nerve-rattling procedures. Two to four times a day he measured dissolved oxygen in the tanks, cast shadows over them, or simulated siphoning operations. In contrast, he disturbed the low-stress group only during weekly cleaning.

After 87 days, fish in the low-stress group showed lower levels of serum cortisol, measured longer, and weighed 30% more than the highly stressed perch. Furthermore, the stressed fish showed no signs of habituating to the repetitive disturbances.

"These results show that it’s important not to disturb yellow perch any more than necessary when raising them for commercial aquaculture," Malison said. "Disturbing them stresses them, and that inhibits their growth rates. You end up with smaller, less healthy fish—and lower profits."

The effects of lighting spectrum were less straightforward. The fish raised under red and full-spectrum light did grow more in length than the others. However, the "red" fish were also more affected by disturbances than the others. Malison says these mixed results suggest full-spectrum lighting at low intensity is probably best, but strong conclusions must await further research.

In his senior year, Head wrote a paper on the project which has been accepted for publication by the Journal of the World Aquaculture Society. In other Sea Grant-supported projects, Malison is currently investigating ways to produce stress-resistant yellow perch and determining the extent to which naturally produced enzymes moderate the effects of cortisol in salmonids.

- John Karl

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Last updated 04 May 2000 by Karl
All contents copyright 2000 University of Wisconsin Sea Grant Institute

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