Inside the colorful Wild Reef exhibit on the lower level of Chicago's Shedd Aquarium sits a small tank containing two warty frogfish, a species found in the waters of the Indo-Pacific region. Each one is about the size of a tennis ball, yellow in color with splashes of red, and covered in wart-like bumps, thus the name.
Jenny Richards, a senior aquarist who cares for a variety of fish at Shedd, calls them "comically round."
"I definitely think they look cute," she says.
Cute — but also cutthroat. This fish is an ambush predator. Part of its dorsal fin operates as a lure that looks like a little shrimp, which it uses to attract its prey.
Last year, the female in the tank began to look a little bloated. And then, in September, she released a spooled-up raft of tens of thousands of translucent eggs, which the male then fertilized.
"Our wild reef aquarists noticed that this was in the habitat, and they quickly grabbed it and brought it behind the scenes for us to attempt to raise," Richards says. And they ended up succeeding in raising just one warty frogfish — now a juvenile named Domino — from those thousands of eggs.
To her knowledge, no one had ever reared a baby warty frogfish before. "It was definitely a little nerve-wracking trying to make sure that we made the most of this rare opportunity," she says.
Though they're not endangered in the wild, climate change, habitat destruction, and collection by traders pose threats to the warty frogfish. And she says the little fish may hold broader lessons for rearing marine creatures.
"This could help us with raising other species in the future," she says. "With changing oceans, climate change, being able to raise these species in captivity is becoming increasingly important."
Tenderly caring for hundreds of larvae
Heading into this effort, the team at the Shedd Aquarium already had a lot of experience raising a variety of other species. But each type of fish has its own specific needs and requires mimicking their open ocean environment in a small 15-gallon tank.
"Marine fish larvae, they're incredibly fragile," explains Richards. "They have completely different habits than the adults have, and they spend their lives floating amongst the zooplankton in the open ocean. We have to be able to have the right lighting conditions, the right flow conditions, the right temperature, and provide the right diet."
So Richards and her team took it slow with the warty frogfish eggs. Within a few days, thousands of tiny larvae had hatched out. "They look very similar to a tadpole," she says.
They rigorously watched the little things, making sure the tank conditions were just right before leaving for the day. Even so, says Richards, "it is very stressful leaving the larvae alone at night."
The aquarists focused their efforts on 500 of them. "If we don't have the proper food, none of them are going to make it past the moment when their yolk reserves run out," she says. But fortunately, the larvae happily fed on the tiny crustaceans called copepods that the aquarists gave them.
Gradually, the larvae underwent a series of dramatic changes. Their vertebrae and fins shifted position. Their muscles changed. And with each iteration, the larval ranks thinned — until there were only three that remained. (This is the case in the wild, too. Very few individual larvae manage to find enough food, avoid stress, escape predation and make it through the anatomical gymnastics of development.)
"We just monitored their behavior every day," says Richards. "If they looked like they were stressed out from too much light, we lowered the light levels. If it looked like they were struggling to swim, we decreased the flow. So just making tiny adjustments to try to make sure that they looked healthy."
Ultimately, at about day 90, just one larva transitioned into a juvenile. This was Domino. It was a pea-sized version of the adult — bright yellow, orange freckles, and its own little lure. It looked like a little fishy Pokémon.
A long road to a fishy future
The Shedd Aquarium is not alone in its pursuit of rearing new marine species. The Mote Marine Laboratory in Sarasota, Florida, for instance, has its own aquaculture research department. Nicole Rhody, the program manager for that team, is impressed with what the aquarists in Chicago managed to do.
"When people are successful," she says, "it's something to celebrate because it's really not that easy to take what happens in nature and be able to recreate that."
Rhody commends how quickly the Chicago team prevailed with the warty frogfish, based on her work trying to rear the common snook, an important sport fishing species.
"Man, I spent probably 15 years of my life working on that animal trying to close the life cycle before we were able to do it," she recalls, referring to the process of getting a fish to spawn and then raising the eggs into adults.
But Rhody says that it's worth the effort — for conservation purposes, and to support commercial and recreational aquaculture.
Back at Shedd Aquarium, Richards agrees. She stands beside Domino's new tank, away from public view. "He's kind of hiding," she says, "but he's in that purple plant. We did watch [him] grow, so definitely a little attached to the baby."
And Richards says she looks forward to the day when Domino can go on exhibit and be seen by the public — a tiny testament to what's possible.
