Stomatopod Log Entry: Terrorism in the Tank (1999)

Contributor:Stephen Barner

"Oh-oh," said Bob Hickey as he peered into the new saltwater aquarium at So. Burlington High School in So. Burlington, Vermont, "I hope that wasn't what it looked like." We had just finished placing the "living rock," former corals that house a plethora of sea life, into the freshly filled tank.

"What did you see?" I asked.

"Well," Bob replied, I thought I caught a glimpse of a Thumbsplitter."

"Which is…?" I pursued.

"It's a kind of shrimp that has a bony protrusion that it can flick out with great force. It's real name is a Mantis Shrimp. It got it's nickname from lobstermen, who found that the little guys could split a finger to the bone. They would sometimes get bit when they reached into their traps."

"Is it a problem?" I asked.

"It'll kill fish," Bob answered. "I'm not sure I even saw it, though. We'll have to just keep our eyes open and see if anything happens."

With all the bustle of getting the aquarium up and running, I forgot about the mystery shrimp while we introduced a few tropical fish into the system and worked on getting out the inevitable kinks. Bob placed three fish in the tank, an active Flame Angel, an iridescent blue Blackcap Basslet, and a well camouflaged and cautious Algae Blenny. All was fine, until a few weeks later when science teacher Rich Wise, who had been a part of the project from the start, introduced an Atlantic Sea Anemone to the aquarium. Soon after this fascinating life form appeared, the Flame Angel disappeared. This was odd, as it had been quite active, swimming to and fro among the rock. We had noticed a problem with its eye that had appeared a couple of weeks earlier, and had thought that it was probably an injury. It was surprising though, to find it gone without a trace.

Just a day or two after the Flame Angel disappeared, the Blackcap Basslet failed to turn up. This beautiful blue fish often hid in the rocks, but recently had become more bold, often venturing out into open water. The school was abuzz with rumors about the missing fish, suspicion was that the anemone had done them in.

According to Hickey, it was indeed possible that an anemone could kill fish--it's tentacles had sufficient sting to render a fish unconscious. I was unsure how the thing could then consume the fish, as it's tentacles did not seem to have the dexterity or strength of octopus or some similar species. At any rate, the anemone was removed from the aquarium. Inspection showed no traces of fish within its translucent body cavity.

To repopulate the aquarium, Wise purchased a school of seven Green Chromis Damsels. All was fine for a few days, until one disappeared. Apparently, our problem had not gone away with the anemone. Students wondered why the missing fish did not float to the top of the aquarium, but apparently, saltwater fish sink when they die, rather than float. We hadn't found a trace of any of the missing fish.

I was standing in front of the tank with Curt Belton, a science teacher, discussing the situation. He was peering into the rocks, looking for signs of the lost fish, when suddenly he exclaimed, "What is that?"

"What's what?" I replied.

"I thought I saw movement under that rock there. It looked like the head of something."

I looked intently at the place he was pointing, and suddenly, like in one of those old submarine sci-fi movies, I saw a shape move slowly and deliberately out from under the dark rock. I saw it's silhouette for only a few seconds. It was about three inches long and had distinct tentacles of some sort coming from its head. Apparently it saw us, as it quickly slipped into an opening in one of the corals and disappeared.

"Wow," exclaimed Curt. "I haven't seen that before."

I explained to him what Bob had told me about the "Thumbsplitter."

"I had forgotten all about it," I said. "I'll bet that's our fish killer. We'll have to get him out of there."

"You've been saying all along that this aquarium is an ecosystem," said Curt. "Predators are part of an ecosystem."

The bell rang, and we both rushed off to our respective classes. The terrorist is still in the tank, and last time we looked, there were still five of the Damsels and the Blenny swimming around. Certainly, the existence of the shrimp will keep us from putting any expensive species in the tank. It will probably also mean that we will lose many of the fish currently in there. It would not be difficult to remove the shrimp. It should merely be a matter of locating the rock in which he is hiding.

What do you think we should do? Should we get rid of this mysterious invader, or should we accept the fact that he is part of the ecosystem, and let matters run their course?

Followup: After much discussion, and several letters from folks on the Internet, we decided to go after the Stomatopod.  I thought that removing the coral would leave it defenseless, but the tenacious little critter hid out somewhere in the crevases, evading our probing eyes, lights and wires.  Finally, we decided to immerse suspect corals in fresh water overnight, in an attempt to kill it.  We spotted the rock that we are fairly sure was its home, as it had signs of an opening that looked as if it had been enlarged.  Now that several months have gone by and we have not lost fish in the same way as before, we are confident that it is gone from the tank.

For a very interesting and informative resource on Stomatopods, visit https://www.keyapa.com/mantis.  This site contains great photos, as well.

Stephen Barner
steve@sburl.k12.vt.us

Web Site Author: A. Sunjian
Site Created February 3, 1998
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