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Dive Dry with Dr. Bill

#662: Plain... or Guadalupe?

I recently wrote about the baby Guadalupe cardinalfish I've been filming in the dive park. I also included an image of a male expelling the eggs from his mouth (and then sucking them back in). Little did I know at the time I would encounter yet another marine biological controversy with them. Well, actually it appears to be more of a controversy to me than to some of the other marine biologists. Such controversies make life interesting, fun and intellectually challenging so I welcome them.

John Moore of divebums.com, a San Diego-based e-mail list server for SCUBA divers asked me to ID a few images of cardinalfish to ensure that they were Guadalupes (Apogon guadalupensis) before he published them on his Photos the Week page. Based on my limited knowledge of cardinalfish, they all looked like the ones I had been observing for over a decade in our waters. After all, Santa Catalina and San Clemente Islands are at the northernmost extent of their geographic range. I knew of no other species in our region until Jovan Shepherd got an image of a bar spot cardinalfish (Apogon retrosella) last month.

John also copied one of the "fishiest" biologists I know, Dr. Milton Love. Milton is a funny guy (in the sense of being humorous) and one of the top fish experts on this side of the continent. If you are interested in the fish from our waters and haven't checked out his incredible tome Certainly More Than You Wanted to Know About the Fishes of the Pacific Coast, I suggest you buy a copy. It is one of my primary field guides when I'm studying our fine finned friends. However, it is too large to take out in the field though unless I have a beautiful assistant willing to carry it for me. I first met Milton back in the mid-1970s when we both worked for Jean-Michel Cousteau on his Project Ocean Search programs, and he guided the Love Lab at UCSB when I was a graduate student there. I had no such luck as a lowly grad student.

Milton informed John and me that there was another species we were unaware of, the plain cardinalfish (Apogon atricaudus). It turned out that several of the fish I filmed belong to this species. Although many unusual warm water fish have entered our waters recently, I had not even considered this one a possibility. Its northernmost range in one of my field guides was listed as Cabo San Lucas. Even if I had opened the pages of Milton's fine guide, I would not have seen it in there. Milton informed us that there have been unpublished records of the fish from not only Guadalupe Island but also San Clemente Island. Who knew?

How can you tell them apart, you ask (don't you?). It all depends. If their dorsal fins (the ones along their back) are held against the body, the plain ones look identical (in my eyes) to the Guadalupe species... and I had a new eye exam recently. However, if their dorsal fins are upright, the "plain" cardinalfish has a dark streak on the forward edge of the first fin. It is hard to detect at night or when the fish is against a dark background. Now I'm always a little skeptical when the difference between two species appears to be so minor. I'll need to do a lot more research in the scientific literature to see if there are other morphological, behavior or genetic differences between the two.

In reviewing my footage of the cardinalfish in the dive park, I have developed a few intriguing biological questions. I'm probably not going to conduct the research necessary to determine the answers. Heck, I'm "retired" and "old guys" just want to have fun (preferably with the girls of similar persuasion as in Cindi Lauper's popular song). I'll leave it to some young biologist who wants to make his or her name doing the tedious stuff. It takes many months and sometimes years to do the research and write the paper, and assuming a scientific journal agrees to publish it, the authors receive no hard cash. I'd rather go off to some exotic dive destination and spend my time filming underwater and drinking a few adult beverages while relaxing in my hammock.

One set of observations has me quite puzzled. Yes, I know... many of my readers think that is my usual state of mind. When I was filming the male cardinalfish carrying the eggs in their mouths, I thought all of them were Guadalupes. I know for certain that was the case with several of them including the one I filmed expelling his mouthful to aerate them. Yet the approximately two dozen baby cardinalfish I filmed appear to be of the plain "persuasion." That leads me to question my sanity... or at least whether these two species are actually distinct. A fact that may help in this quandary is that the plain cardinalfish are said to reach a maximum length of about three inches while the Guadalupes can get nearly twice that size. Is it possible that the dark streak on the forward dorsal fin is simply a juvenile trait? Inquiring minds want to know.

Unfortunately when I went to relocate the babies last weekend, I could only find one on two dives. Instead of the little kiddies, I noticed two morays in their hole which looked very "pleased" with themselves. At first I feared that the youngsters became hors d'oeuvres for the nasty eels. Hopefully they simply vacated their former home and found a new hiding place in the Casino Point breakwater. Sadly they didn't leave a forwarding address for me, so I'll have to continue searching for them to further investigate this intriguing question. Ah, the sacrifices I make in the name of science!

© 2015 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 29, 10:00 AM weekdays and on Charter Communications Cable channel 33 at 7:30 PM on Tuesdays in the Riverside/Norco area. You can also watch these episodes in iPod format on YouTube through my channel there (drbillbushing). 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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Guadalupe cardinalfish (left) and plain cardinalfish (right) showing dark streak on dorsal fin.

This document maintained by Dr. Bill Bushing.
Material and images © 2015 Star Thrower Educational Multimedia