The delta smelt (Hypomesus transpacificus) may be all but extinct in the wild, but it turns out that hope is not quite lost for this controversial California fish.

Although a recent survey turned up only six delta smelt in the Sacramento-San Joaquin estuary, they are not alone. Another 20,000 of the tiny fish currently live in captivity at the Fish Conservation and Culture Laboratory at the University of California, Davis.

This massive assurance breeding population—the only one that exists—got its start several years ago when the laboratory received about 160 wild fish, says Dr. Joan Lindberg, the lab’s director emeritus. The fish have been bred there ever since and the lab provides a few smelt every year to the Livingston Stone National Fish Hatchery, which maintains a secondary safeguard population.

It’s a lot of work to keep the captive smelt alive within the two-acre UC-Davis facility. “The smelt require an intensive style of aquaculture,” Lindberg says. The water is constantly recirculated, the temperature is controlled (the fish get stressed above 71 degrees) and biofiltration processes clear the water of pollutants. Small crustaceans and insect larvae are constantly added to the water as prey.

The smelt also live in different parts of the facility depending on where they are in their life cycle. “The fish move from smaller to larger systems as they grow,” Lindberg says. “We can keep adults in a system of 5-foot-diameter tanks.” (You can see photos of the tanks on the lab’s Facebook page.)

The fish aren’t all kept together. Instead, the lab divides the population into about 260 “sibling families” every year. Each fish is tracked and recorded and only allowed to breed with matches pre-selected by the UC Davis Genomic Variation Laboratory. “By making very selective crosses and knowing the pedigree and the parents of each individual, we can minimize inbreeding,” Lindberg said.

In addition to the labor-intensive processes, keeping the fish alive in captivity is also expensive. The lab just received a nearly $10 million from the U.S. Bureau of Reclamation, which will fund the work for the next four years.

Will any of these fish ever make it back to their home in the Sacramento-San Joaquin estuary? Lindberg says “putting animals back in this system would be problematic. We would hope to see some improvements to the habitat before we do that.”

That’s unlikely to happen any time soon, though. For now, a combination of vats, tanks and hard work is the only thing keeping the delta smelt from extinction.

Photo: UC Davis