The arapaima is the Amazon River's largest fish species. It's also one of the most imperiled, having been overfished and pushed to the brink of extinction. Officials say the giant fish is now "locally extinct" in many areas.

An international team of scientists recently surveyed villages and fishing communities in the Brazilian state of Amazonas to find out more about the health of arapaima populations. The researchers found the species is now missing from many areas in the Amazon where it used to dominate the food chain. The arapaima can grow up to ten feet in length and weigh upwards of 400 pounds.

Researchers used their efforts as a way to pit two fishing conservation and management theories against each other -- bioeconomic theory and the lesser-known "fishing down" theory.

Bioeconomic theory posits that the principles of market economics would help protect species like the arapaima. But "fishing-down" suggests high-value, easy-to-catch fish are vulnerable to overfishing and unprotected by marked forces.

"Bioeconomic thinking has predicted that scarcity would drive up fishing costs, which would increase price and help save depleted species," explained Leandro Castello, an assistant professor of fisheries in Virginia Tech's College of Natural Resources and Environment. "If that prediction were true, extinctions induced by fishing would not exist, but that is not what has happened."

Castello lead the recent arapaima research effort. The work of he and his colleagues was recently featured in the journal Aquatic Conservation.

Arapaima are one of only a few fish species that can breath air. They have one lung in addition to a gill system, which has allowed them to survive in low oxygen waterways for thousands of years. But that ability to rise to the surface and gulp down oxygen also makes them vulnerable -- easy to spot for fisherman armed with spears.

The research didn't reveal only bad news. Scientists found that in communities where fishing regulations have been enacted and enforced, the arapaima is thriving.

"Many previously overexploited arapaima populations are now booming due to good management," Castello said. "The time has come to apply fishers' ecological knowledge to assess populations, document practices and trends, and solve fisheries problems through user participation in management and conservation."