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Dive Dry with Dr. Bill

#369: Zebra... Perch... Chub

Last week I wrote about the halfmoon, a member of the sea chub fish family Kyphosidae. I thought this week I'd keep it in all in the family and write about a relative, the zebra "perch." Yep, yet another fish commonly referred to as a perch... but nothing like the perch I used to catch when I sat on the dock while managing the waterfront at a sports club back in my Chicago high school days. And, yes... those were the days. My entire guard staff was composed of lovely ladies... but I digress (as usual). You're here to read about zebras... er perch... I mean zebra perch.

This sea chub species is known by us scientific types as Hermosillo azurea. The species has been recorded from the mouth of the Klamath River in northern California south past Cabo San Lucas and into the Gulf of California. There they are mostly found in the northern and central region of that body of water, known to many as the Sea of Cortez. Now since Hernán Cortés de Monroy y Pizarro, 1st Marqués del Valle de Oaxaca was the conqueror of the Aztec Empire and brought much of Mexico under Spanish rule, I wonder how the native people down there feel about this name. But again I digress... back to zebra perch. They are another species of schooling sea chub generally found in shallow water above 25 feet. They are often seen around kelp beds and off both rocky and sandy bottoms.

Zebra perch may reach up to about 18" in length. The body is a light gray in color, appearing almost bronze at times. It has 9-10 dark vertical bars on each side. Looking closely at the mouth you can see the similarity with other local sea chubs like the halfmoon and opaleye. They have a bluish spot on the operculum or gill cover, and may have a dark patch at the base of their pectoral fin located on the side of the body near the front. Many other species of chubs have scales on their heads, but this species lacks them. The teeth in their jaws are fixed, unlike those in some other, mostly tropical sea chubs.

The diet of the zebra perch was described as being partially herbivorous (a half hearted vegetarian) to "feeding on marine algae" to having a diet of macro (big) and micro (small) algae on the bottom. Fortunately my research uncovered a study of their dietary habits right here off Catalina Island. I'm going to elaborate on these findings because they offer insight into fish diets and morphology. Researchers Sturm and Horn determined that the zebra perch was almost entirely herbivorous with less than 1/10th of one percent of their food in the form of animal tissue. I could never survive such a diet... I tried to be strictly vegetarian back in the late 1970s. Ugh!

Of the algae found in the stomachs of these fish, red algae dominated at over 88% while brown algae were just under 8% and green algae constituted a mere 4% of the total. The single most important dietary component were the filamentous red algae species in the genus Polysiphonia (sorry, no common name). Since this alga is a very minor component of the seaweeds on rocky reefs, this means zebra perch are very selective feeders. If they were your kids, you'd refer to them as "fussy eaters." We scientists would say this species has a very narrow niche as far as food goes. They were found to digest certain species of brown algae like the introduced Sargassum muticum which has high levels of polyphenolic compounds, organic chemicals that usually ward off herbivores.

Herbivorous fish often have long, coiled digestive tracts to digest the algal or plant material. That of the zebra perch is four times as long as the fish itself. Hmmm, just how do they pack all that in there? Algal meals are digested in two ways. In the stomach, digestive acids are used to break them down. Then in the gut or intestinal tract, these fish use the same basic mechanisms as a dairy cow. Bacteria break down the matter through fermentation. However, to the best of my knowledge they do not chew their cud.

Zebra perch seem to be much more active swimmers than their local sea chub relatives. In fact, I'd almost refer to them as almost frenetic as they speed past me underwater, darting around in almost unpredictable ways. Their halfmoon brethren seem much more sedate by comparison. Like the other sea chubs in our region, they are pelagic spawners, releasing their eggs into the water column where they are fertilized. Although they are often seen in small schools, on one occasion I observed a group of possibly thousands of these fish swimming by me at Long Point. I assumed this was a spawning event so I turned my camera on to capture a little "mating." The larvae drift in the plankton until they are ready to settle out. One very interesting observation I've made is seeing young zebra perch apparently cleaning other fish like topsmelt. Perhaps the juveniles need a bit more animal protein in their diet than the adults.

The sea chub family is largely tropical in distribution. Scientists have noticed that sightings of zebra perch in the southern California Bight have increased in recent decades. It is believed that this may be due to oceanic warming as part of global climate change. As the waters in our region increase in temperature, the geographic range of the zebra perch may expand northward. We've also had sightings in Lover's Cove of the blue bronze chub, another warmer water sea chub species. Of course I'm still waiting until the waters warm up enough to find coral reefs in the dive park. Yes, I know... "wishful thinking." I'll just have to visit a few tropical dive sites this winter and make believe!

© 2009 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 and on Charter Communications Cable channel 33 at 7:30 PM on Tuesdays in the Riverside/Norco area. Please help me climb out of self-imposed poverty... buy my DVD's (see this link). Yes, take Dr. Bill home with you... we'll both be glad you did!

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Individual zebra perch showing the species' features including the typical sea chub mouth;
zebra perch in small group and in dense spawning cluster.

This document maintained by Dr. Bill Bushing.
Material and images © 2009 Star Thrower Educational Multimedia