It's still March but soon enough, smallmouth bass will be on the nest--late April in Arkansas, and early June in Wisconsin. Ardent anglers know that nest-guarding smallmouth bass put all their attention in guarding their young, with little energy put into feeding. Now, fish physiologist Dr. Kyle Hanson at the Abernathy Fish Technology Center in Washington knows why. Hanson and colleagues Drs. Alfonso Abizaid and Steven Cooke from Carleton University delved into the cause and consequence of anorexia in smallmouth bass. The answers were found in looks at blood chemistry and manipulations in feeding. Their findings were published in the science journal, Hormones and Behavior.
Hanson and his colleagues caught nest-guarding male bass and took blood samples over the course of the period that offspring progress from eggs to fry and their eventual independence from the parent. They tested the blood for the hormone, gherlin, which is known to regulate appetite. They learned that the hormone is lowest in guarding males when their offspring are in the egg stage. It increased as the young grew toward independence, a period that lasted about three weeks.
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| Dr. Kyle Hanson and colleagues tested the aggressiveness of anorexic smallmouth bass, and published their findings in the science journal, Hormones and Behavior. Marie-Ange Gravel/Carleton University |
The scientists also injected groups of nesting bass with gherlin and force-fed crayfish to others and tested their swimming abilities and aggressiveness toward nest predators. Fish with full bellies didn’t swim as well; similarly, sated bass were less aggressive after eating. The research reveals that anorexia actually allows male smallmouth bass to better protect offspring.
