An oceanic rainbow surrounds visitors stepping up to the top floor of the Adventure Aquarium in Camden, New Jersey. The sun steaks in through tinted windows of Kaleidoscope Cove, a new exhibit where color is everything. Fish grouped in separate tanks by their respective colors put the rainbow hues of marine life in full glory. Like a colorful quilt, household favorites like blue tangs (Paracanthurus hepatus) and orange and white clownfish (Amphiprioninae) glisten alongside some lesser known fish like striped harlequin sweetlips (Plectorhinchus chaetodonoides) and blazing red fire shrimp (Lysmata debelius). An inviting touch tank filled with reddish sea stars beckons the young and young at heart. Even a glowy, fan-favorite axolotl (Ambystoma mexicanum) and various poison dart frogs get their chance to show off.
"We are sharing those color stories to show all the different ways that animals exhibit their adaptations to color and pattern," Adventure Aquarium Collections, Conservation & Development Coordinator Alicia Longo tells Popular Science during a recent visit. "And that's really relatable to the public. Everybody can relate to a rainbow of color."
Kaleidoscope Cove features over 100 different species, at least 10 of which are new to the 33-year-old aquarium just across the Delaware River from Philadelphia.
"I think for the biologists specifically, it's very rewarding to be tasked with learning about a new species," Longo says. "It's just a joy to learn those new things and just have that knowledge of a new species and share with the public. That's why we're here, right?"
Fish use their colors as a means of communication. The mechanics of how they physically display color occurs deep at the cellular level-and involves some crystals in serious positions of power.
Pigment-containing cells called chromatophores are present in fish skin. "Within these chromatophores are chromatosomes," Simon Thorrold, a fish ecologist at Woods Hole Oceanographic Institution in Massachusetts who was not involved in creating the new exhibit, tells Popular Science. "These are crystals that come in different colors and within that one cell, you'll have a bunch of crystals that will all be the same color."
While each crystal is the same color, the skin cell next to it can express a different color. The adjacent crystals can then determine the amount of light that passes through it by controlling where they are within the cell.
"So if you spread them out, they're going to shade more and the color is going to be dark," says Thorrold. "If you spring them into the middle, they're going to shade less and you're going to have more transparency."
Color serves many purposes for the world's fish. It can help them find mates, communicate with those in their school, and for protection. Some fish like flounder use it to camouflage along the sandy and rocky seafloor. Color could also be a serious warning sign to other organisms.
"Animals that are exhibiting bright colors might not necessarily be toxic, but may be mimicking other animals that are toxic," says Longo. "A good representation of that in Kaleidoscope Cove is our harlequin sweet lips."
As juveniles, they will mimic the pattern and behaviors of soft-bodied marine gastropod molluscs called nudibranchs. These striped, shell-less molluscs also called sea slugs come in a variety of colors (blues, purples, and oranges). They also steal venom away from toxic animals and use it to their advantage. By imitating them, the young harlequin sweet lips are likely sending a strong message to swim away.
"Fish are perhaps visual in the same way that we use audio cues," says Thorrold. "So I think, they do use color for all kinds of things because they don't quite have the same sound repertoire that we do."
Amidst all of the vivid colors in Kaleidoscope Cove, a deep purple, dark room opposite to the sun-streaked touch tank stands out. Inside the Glowing Grotto, visitors can see the bioluminescence in action, including glowing corals and the blinking splitfin flashlight fish (Anomalops katoptron). This species found in the Pacific Ocean is known for the head lamp-looking light on its head that helps the flashlight fish communicate with its school, confuse predators, and attract prey.
"They are very unique reef species, where they dwell in really dark caves throughout the day when it's bright," says Longo. "So they stay a little bit deeper, but they have a light producing organ underneath their eye. It's called a photophore and inside that is a bioluminescent bacteria."
The bioluminescence itself is generated by a chemical reaction within the bacteria and not by the fish itself. However, flashlight fish have the ability to essentially turn this bacteria on and off by moving it around within their eyes. That movement creates the "blinking" patterns that they use to survive.
However, fish bioluminescence is not controlled by bacteria alone. Some fish have intrinsic bio bioluminescence, where they can produce that glow on their own. Lantern fish (Myctophidae) living in the ocean's deep mesopelagic zone use light-producing organs called photophores that don't rely on bacteria or a chemical reaction to glow.
According to Thorrold, hunting is one of the most interesting ways that lantern fish use bioluminescence.
"If you're a lantern fish, you're at about 500 meters [1640 feet] deep during the day. It's very, very dark, but if you look up, you can still see a little bit of light," Thorrold explains. "They're actually evolutionary designed to look up for silhouettes. And that's how they hunt, by looking up for silhouettes. Their prey is just breaking that little bit of downwelling light enough to make a silhouette."
Still, this mesopelagic arms race continues. Some prey species use their own photophores to countershade and create light that makes the silhouette go away-so the lantern fish can't see them.
"So now the predators don't see anything. They look up, there's a fish there, but it's mimicking exactly the downwelling light. It effectively disappears, so that's the camouflage," explains Thorrold.
While our finned friends use color or bioluminescence to communicate with each other, one of the key human messages central to Kaleidoscope Cove is that of conservation. Even with these evolutionary adaptations and advances, these fish need our help. According to the United Nations, the world lost 14 percent of its coral reefs between 2009 and 2018 due to the pressures of climate change. And the stress has only continued. From January 1, 2023 to August 20, 2025, bleaching-level heat stress has impacted 84 percent of the world's coral reef area. Without those corals, many of these beautiful fish won't have a home.
"The majority of those animals up there are Indo Pacific reef species. We are big advocates for coral conservation and sharing the global coral crisis that we're experiencing right now," says Longo. "So we share a lot of that with our guests, to not only raise awareness, but give them an action to take home with them that they can easily put into their everyday habits."
These creative, helpful, and simply fascinating adaptations offer a way to ignite conservation and build bridges between the aquatic and terrestrial worlds.
"All of these super cool adaptations that life on planet Earth has figured out to make it such an amazing place, just makes me feel very protective of what we have," says Thorrold. "The beauty that's here and the amazing engineering that evolution has done to generate this makes me feel very small, but at the same time super connected to this planet that we do have."
It's a rainbow connection on full display in Camden.