The Shark Lady and Convict Fish
By: Susannah Costello
Famous shark researcher, Dr. Eugenie Clark, helped found Mote Marine Laboratory in 1955. While she's known worldwide for her shark studies and her popular work, "The Lady and the Sharks," was a best-seller, small fishes still fascinate her.
Some of her recent discoveries include the unusual behaviors of the seldom-seen adult Pholidichthys leucotaenia, or convict fish, in the wild.
Question: What’s a famous shark researcher like Eugenie Clark doing studying an ordinary reef fish like the Pholodichthys leucotaenia?
Answer: First of all, the whole shark thing was overdone. When I was beginning, I did a lot of work with sharks - especially when I started this lab. We were just beginning to learn a lot about sharks and there was attention paid to that. People remember that. Maybe more than is warranted.
And as for the “ordinary reef fish”… Pholidichthys leucotaenia is fascinating. Fascinating!
Q: Isn’t it a common fish you find in pet stores?
A: That makes it all the more interesting. Some people do raise these fish in aquariums. The problem is that when the fish grow to about 9 cm, they disappear. They burrow into a labyrinth of tunnels they construct and, as adults, never come out. Nobody knew what went on in the tunnels until we put a Kogge endoscope in.
One interesting thing about this fish is a theory on how the adults feed. All babies swim out at dawn and swim all over the place, feeding on plankton. They return to the adults with their bellies bulging. Then we found the adults putting their babies in their mouths and then releasing them. We think maybe that the babies are bringing them food. If the babies are regurgitating food to the parents, it’s unique in nature. There are examples of parents regurgitating to babies. Birds regurgitate food to their young and bats regurgitate blood to their young but this may be the first example of the young feeding the adults.
Q: Are you sure it’s not cannibalism?
A: We don’t think so. We see the babies come back out of the parents’ mouths.
We have also opened up the parents’ stomachs and examined the contents and there are no signs of the babies, only fully digested liquid that could be the plankton regurgitated by the babies.
Q: So pet store fish owners are missing out?
A: In nature, the babies go out to feed by the thousands and can travel as far as 50 meters from their burrow to eat plankton. And at times, they swarm in huge balls that explode like fireworks and contract repeatedly. Sometimes, the swarms completely leave the reef and stream far out into the open water in long snake-like formations.
Q: Recently you spoke at the annual conference of the Society of Icthyologists and Herpetologists about your studies of Pholidichthys in Papua New Guinea. You noted some dramatic changes the convict fish experiences as it matures.
A: As babies, the fish leave the tunnels at a certain time every morning, go out to find food and come home at the same time every night. But as adults, they spend their lives in tunnels. They never go out. As babies, they can be as small as 1 cm and we’ve seen them as large as 9 cm before they disappear into the tunnels. As cryptic adults, they can get to be as large as 57 cm.
Q: Were you the first to actually observe the adult pholys in the wild?
A: Yes, that was in Papua New Guinea in the spring of 1999.
Q: Was that when you focused on Pholidichthys as your primary research subject?
A: Pholidichthys have been one of my main research projects since 1996 and since 2001, the major part of the research we’re doing in Papua New Guinea and the Island of Mabul off North Borneo. Here at the Lab we’re raising them in an experimental aquarium with less than 2 cm of sand and a fiberglass tunnel that is open against the aquarium glass so we can observe them. The juveniles go in the artificial tunnel to eat, so we’re hoping they’ll also breed there.
Q: Can you tell individuals apart easily?
A: Oh yes, the fish are clearly differentiated. They have a black-and-white-striped pattern that changes as the fish mature and appears to be different on each side of each fish.
Learn more about: Shark Research
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Mote Marine Laboratory has been a leader in marine research since it was founded in 1955. Today, we incorporate public outreach as a key part of our mission. Mote is an independent nonprofit organization and has seven centers for marine research, the public Mote Aquarium and an Education Division specializing in public programs for all ages.
