The patients are farm-raised steelhead trout and salmon. Researchers put them to sleep for a few moments, and then place small radio transmitters inside their bellies.
Later this week, a team led by Dr. Peter Klimley, will release the fish into the Sacramento River. The US Army Corps of Engineers wants to know what effect dredging might have on fish making their way out to sea.
"By dredging, you change the topography of the bay. You create all these channels, and in fact they are false channels," said Kimley, Ph.D.
There are seven receivers beneath the bridge in Crockett, and some 300 of them placed between the river, the bay and the Golden Gate.
"It's like a tape recorder. It records the date, the time, and the name of the fish, or in this case, its number," said Kimley, Ph.D.
Each of these small transmitters costs $350. The data is invaluable at a time when salmon and steelhead populations have reached record low numbers.
Last year, only 10 percent of the fish they tracked made it to sea.
"We think the way they do it is by detecting the flow, and then moving with it," said Kimley, Ph.D.
"If the fish aren't there, then we will have a problem because it reflects on the ecosystem. And we need the ecosystem to be healthy for us to stay healthy," said marine biologist Michelle Buckhorn, Ph.D.
Depending on results, the Army Corps could suspend dredging, or stay away from particular areas when it knows the fish are moving. At a time like this, every fish really does count, which is why they are trying to count them all.
"Here we think we get every fish," said Kimley, Ph.D.