What you see is what you get

Research throws light on fish vision

An anasthetized and paralyzed spotted seatrout prepared for a fish-hearing experiment at the Eastern Shore Lab in Wachapreague. Photo by Andrij Horodysky.

VIMS graduate student Andrij Horodysky monitoring the progress of a vision experiment using an Atlantic croaker (Micropogonias undulatus).

Andrij Horodysky’s research can be summed up in a simple saying—what you see is what you get. Horodysky, a VIMS Ph.D. student with professors Rich Brill, Rob Latour, and Jack Musick, is using electroretinography—a technique first developed for studying human vision—to explore how fishes see the underwater world of Chesapeake Bay.

The team is focusing on recreationally important species such as striped bass, weakfish, croaker, and drum. This reflects the source of their funding, which comes from the Recreational Fishing Advisory Board of the Virginia Marine Resources Commission. The Board uses saltwater angling fees to fund projects that improve the Commonwealth’s recreational fisheries.

Horodysky’s early results provide basic insight into how Bay fishes see the world. They show that some species, like striped bass, are adapted to see large, swiftly moving prey in daylight. Others, like weakfish, are adapted to see small, sluggish prey at night.

He’s also comparing the types of prey that fishes are adapted to see and eat with the prey items that are actually in their stomachs. He’s found an intriguing disparity in striped bass, whose eyes are built to see fish such as menhaden, but whose stomachs mostly contain juvenile blue crabs and shrimp.

Horodysky and Brill hypothesize that stripers are living in a visual world very different from the one evolution prepared them for. “Chesapeake Bay used to be very clear,” says Brill. “Now we’ve made it mucky. Our argument is that over evolutionary time these fish made certain visual choices, then suddenly find themselves in a visual environment they didn’t evolve in.”

This visual mismatch could have important implications for fisheries managers, who traditionally make management decisions based on the relative abundance of predator and prey—the number of striped bass or menhaden netted per unit area.

“What we’re getting at,” says Horodysky, “is that it isn’t the number of prey per meter that’s most important to these visual predators. It’s the number they can see. If you can’t see very far, how is that affecting your ability to feed? These are larger questions we can begin to chip away at once we get our baseline data. We can’t start to answer these questions until we know the limits of the eye.”