Zoological Investigations

I went snorkeling in Puerto Rican waters on my day off this week. Yes, that’s right. I will rub it in, thank you. Even though the saltwater burned every scratch and cut I have from climbing up 24-foot tall ladders into sketchy, thorny mesquite trees working with smooth billed anis all day, it was damn worth it. I saw all kinds of things I can’t even remember right now, and it was awesome. I am so tired the only thing I can remember is the name of one fish: the sergeant major damsel fish, Abudefduf saxatilis. Abudefduf saxatilis! Now is that funny or am I just exhausted? Likely both.

Everyone is familiar with that fun loving clownfish, Nemo (Amphiprion sp.). But Nemo is just the tip of the iceberg here in this great new edition of Zoological Investigations. Clownfish are commensal with anemones, a sessile marine animal related to coral. And here comes the crushing blow: just like most things you loved in childhood, you grow up and find out that Nemo is in fact not a true anemonefish but a false anemonefish.

Now A. percula on the other hand, which looks almost exactly the same but behaves slightly differently, is a true anemonefish. Anemonefish have a mucous coating that protects them from the anemone’s sting. In exchange for living a well-protected life amongst the stinging, otherwise fish-eating anemones, clownfish keep the anemones free of parasites and defend them against potential predators. What does this have to do with sergeant majors? Sergeant majors and clownfish both belong to the family Pomacentridae. Named for the five black stripes that run vertically along their body like a military insignia, sergeant majors can be found in — yes, you guessed it — Puerto Rico, as well as basically everywhere else that has shallow tropical reefs in the Atlantic Ocean.

Sergeant majors are aggressive and will vigorously defend their territory against intruders of all kinds. Male majors build nests and chase females around all morning, trying to get her to lay her eggs, up to 200,000, in his nest. If she does, he will fearlessly guard them until they hatch about 160 hours after he has fertilized them. When a male sergeant major is in an egg-guarding way, he takes on a more stunning bluish hue than usual, as if saying to predators, “Back the hell off ’fore things get nasty!” By the way, egg guarding by males is a characteristic of the family Pomacentridae, so it isn’t such a surprise that Nemo’s father was a great dad. Although in real life Pomacentrids don’t bother after the larvae are big enough to swim around on their own.

As it turns out, Carl “The Man” Linnaeus himself blessed the sergeant major with its incredible Latin name, Abudefduf saxatilis, in 1758. According to scienceray.com, Abudefduf means “father,” saxa translates as “living among rocks” and tilis refers to something that is “tile-like in colour.” How true, how evocative!