Dive Dry with Dr. Bill

053: Opaleye

Sometimes I think these fish are the Rodney Dangerfields of our marine world... the just don't get no respect! Some even refer to them as "trash fish." How insulting and demeaning, but true. They just aren't a good fish to place on a dinner plate based on very limited experience (1 sample) in my early years here. Despite this they are often taken by "recreational" fishers close to shore in our region. Their bones have also been found in Native American kitchen middens (referred to as trash heaps today).

Opaleyes have beautiful blue eyes (like mine) from which they get their name. Although commonly referred to as opaleye perch because of their similar body shape, they and their halfmoon relatives are actually members of the sea chub family. The grey- to olive-green bodies have one to three yellowish spots on the back below the dorsal fin. I have photographed an individual in Catalina's Dive Park with five spots on each side. Apparently fish off Baja tend to have more spots than those in our waters. Perhaps the one I saw was a tourist (or visitor if you prefer).

Found from Oregon to southern Baja, these fish are most common south of Pt. Conception in the Californian biogeographic province (remember your biogeography?). The young are frequently seen in tidepools where they fed on invertebrates and are protected from large predators. Milton Love indicates that these young fish are actually able to breathe air, which is important since small tidepools may have their oxygen depleted at times. After a few years these fish move out of the tidepools and onto the reefs and into the kelp forest. Here they can be seen as deep as 100 feet but usually shallower.

Opaleye can be seen individually feeding on the bottom, or in aggregations in the kelp canopy or shallow water. Large individuals may exceed two feet in length. Adults shed their eggs in the water column in late spring where they drift as plankton for a while before the young enter the tidepools.

Opaleye are thought to be vegetarians because they eat algae, including giant kelp. I often see them taking bites out of kelp blades or feather boa fronds as well as seaweeds on the rocks. If true, this truly makes them a southern California fish! However, they are not vegans... in fact their diet will also include the occasional invertebrate such as shrimp. Like the "vegetarian" who sneaks a Big Mac on occasion, these fish may actually be closet omnivores!

It has been suggested that in taking bites out of the kelp they are actually feeding on the many invertebrates encrusted on it. I have tried to observe the portions of the kelp blade which they attack, and anecdotally they do appear to bite areas that are covered with bryozoans, hydroids and other "flesh." I have also observed opaleye repeatedly pecking at topsmelt, possibly cleaning them by taking parasites from their bodies. I have never heard of this behaviour observed or reported elsewhere.

I have noticed what may be highly significant differences (scientifically speaking) in the numbers of opaleye when I dive the Casino Dive Park and Lover's Cove here on Catalina. Opaleye constitute a much higher percentage of the fish population in Lover's Cove. Both were declared reserves in the 1960's and have somewhat similar habitat conditions, so I don't think these factors are the cause. My guess is that the artificial feeding by the glassbottom boat operators may be a major factor in this. Since they are not feeding the fish kelp or other algae, it appears that opaleye are not adverse to a little anchovy (in the past) and fish meal pellets. This seems to add credence to the belief that they are omnivores. Does feeding the fish here matter? Perhaps ecologically but since we can't fish for them in the reserves I'm not going to raise a big stink! Why bite the hand that has occasionally "fed" me?

Whatever it is they are really feeding on, there are a few animals that don't mind their taste (unlike me). These less fussy eaters include sea lions, cormorants and Catalina's bald eagles. Perhaps they possess greater culinary skills than I do.

© 2003 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 49, 10:00 AM and 5:00 PM weekdays.

Image caption: Individual opaleye with single white spot; group of opaleye in open water;
opaleye feeding in kelp canopy; opaleye feeding on shallow bottom

This document maintained by Dr. Bill Bushing.
Material © 2003 Star Thrower Educational Multimedia