Croaking Croaker

January 19, 2008
By Damond Benningfield

It sounds like a plot device from a sci-fi movie. Organisms don’t have enough oxygen to operate normally, so they start to shut down some of their systems to save energy -- a sort of low-grade suspended animation. One response is basically to stop having babies.

Atlantic Croaker. Credit: Illustration by Diane Rome Peebles - Florida Fish and Wildlife Conservation Commission (FWC)

But in the case of Atlantic croaker, it’s not fiction -- it happens when the oxygen level drops in their coastal habitats. It’s probably a normal adaptation to help them survive in times when the oxygen level drops naturally. But it could have a big impact on the health of the entire population.

Researchers from the University of Texas Marine Science Institute studied Atlantic croaker in Florida’s Pensacola Bay and in their lab in Texas.

They found that in parts of the bay where the oxygen in the water was low, young croaker didn’t produce mature eggs and sperm, because their reproductive organs stopped developing. And the lab tests showed that with low levels of oxygen in the water, the fish stopped making the hormones and enzymes that help the reproductive organs develop.

This was the first time that such a response had been measured in saltwater fish. And although it’s probably normal, scientists also find it worrisome. Runoff from agriculture and land development are reducing the oxygen levels in much of America’s Atlantic and Gulf coastal waters. If that causes fish to quit reproducing, then entire populations could be at risk -- something that’s as scary as any sci-fi plot.