UV and Perch Spawning

Yellow perch typically spawn when temperatures at spawning depth range from 45°F to 50°F, as females produce an accordion-like gelatinous egg mass, frequently draping them on vegetation or submerged wood. A team from Lehigh University studied the relationship of depth, temperature, and solar ultraviolet radiation (UVR) on perch spawning in two lakes in Pennsylvania.*

Lakes with high levels of dissolved organic carbon (DOC) tend to be darker in color than those with low levels of DOC as the organics filter out radiation that's known to be lethal to fish eggs. For example, at murky Lake Lacawac, 99 percent of UVR was filtered out at a depth of 1½ feet, while at clear Lake Giles, that level of shading wasn't reached until a depth of 16 feet.

But temperature also plays a role, as eggs develop faster in warmer water and survive at a higher rate. This suite of factors suggests that perch face conflicting selective pressures. Egg survival, in theory, should be higher at depths that balance the lethal effects of radiation with the benefits of solar heating.

The scientists found that at Lake Giles, with low DOC and high UVR, perch laid eggs in water from 7 to 33 feet deep, with most between 16 and 19 feet. At murky Lacawac, maximum spawning depth was just 5 feet and most were 2 feet deep. They note that dissolved oxygen can play a role, particularly in high DOC lakes, and perch may select objects to drape eggs on to prevent them from falling into low-oxygen zones.

*Huff, D., G. Grad, and C. E. Williamson. 2004. Environmental constraints on spawning depth of yellow perch: The roles of low temperature and high solar ultraviolet radiation. Trans. Am. Fish Soc. 133:718 — 726.

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