Old Lyme — If something’s fishy, Sadie, Hunter and Ruger will be the first to know.

The three Labrador retrievers, part of the state Department of Energy and Environmental Protection’s K-9 unit, will be employing their newly acquired fish detection skills on opening day of fishing season Saturday, when they’ll be patrolling the state’s lakes, rivers and streams with their Environmental Conservation Police officer-handlers.

“Mostly we see compliance (with fishing regulations), but some people do get creative in the way they try to hide things from us,” EnCon Capt. Ryan Healy said Friday morning, before a demonstration with one of the dogs.

The dogs are able to detect fish hidden in closed boat compartments, cars, under rocks and just about anywhere else, Healy said.

The dogs have been trained with three of the most popular game fish — trout, striped bass and blackfish — but can detect any species of fish hidden from view, Healy said.

Susan Whalen, deputy commissioner of DEEP, said the dogs will serve as a deterrent to anglers keeping fish under the legal size, caught out of season or who are trying to keep more fish than the legal limit. Fines for illegally caught fish are $75 per fish and higher.

“They have a serious job to do, and they’ll be a great asset to the force,” she said.

During the demonstration at DEEP Marine Headquarters, Officer William Logiodice led his K-9 Ruger to a vessel tied to the nearby docks. When Logiodice commanded Ruger to “seek,” the dog jumped on board, circled the cabin, sat beside a closed compartment and stared intently at Logiodice. The dogs are trained not to take the fish in their mouth but simply to signal their find by sitting in place, Healy said.

Ruger’s reward? A toss of a well-worn tennis ball.

“Good boy,” Logiodice said, patting Ruger and throwing the ball.

j.benson@theday.com

Twitter: @BensonJudy