Bigfin reef squids are on view for the first time at Shedd Aquarium. Hatched at Shedd, they glide to and fro, like milky apparitions, in the large habitat on the mezzanine level of the Abbott Oceanarium.
On first look, many guests think that these are cuttlefish because of the broad fin—hence the name bigfin—that runs along the entire length of each side of the mantle, or body. That’s a good guess. Squids are cephalopods, like cuttlefishes and octopuses, and they share a common body plan: a head, with brain, eyes, beak and mouth; a mantle, with the main organs; and arms or tentacles, or both. (Chambered nautiluses, the remaining cephalopod group, add a shell.)
Squids have eight arms and two longer tentacles, all lined with toothed suction cups for holding prey. A squid uses the extendable tentacles to capture fishes, prawns, crustaceans and mollusks, while its arms move the food headfirst to the sharp beak.
While all octopuses and cuttlefishes are venomous, the bigfin reef squid is among a number of squid species that do not have a venom gland associated with the beak. Instead, the squid dispatches a fish by quickly piercing its spinal cord, then rips off and drops the head and proceeds to consume the body. This behavior is so ingrained that Shedd’s squids will not accept frozen fish with the heads off.
Here’s looking at you, squid
As you gaze at these otherworldly creatures, you may get the impression that they’re looking back at you. They are, and with eyes that function a lot like ours. (For the well-being of the sensitive squids, please respect the stantions placed in front of the habitat, and do not use the flash on your camera.) While squid (and octopus and cuttlefish) eyes are different in structure from ours, they focus on objects near and far and provide clear images. Another common name for bigfins is green-eyed squids, for the iridescent pale green coloration around their eyes.
When it comes to color, squids, like octopuses and cuttlefishes, are masters of the quick change. Bigfins have three kinds of cells in their skin that let them hide in plain sight from predators or stand out in a crowd to potential mates or competitors for food or space.
Covering the top of the head, mantle and arms are chromatophores, large cells filled with sacs of pigment that can be individually controlled at will to turn the squid pale yellow, brownish pink, dusky violet, or pale red in milliseconds. Iridophores reflect light to give areas of the head a metallic green sheen. And leucophores reflect ambient light, so a squid can appear white in white light or pale blue in blue light. Employing all of these cells together, bigfins also create complex body patterns of speckles and squiggles, a capability for camouflage that they have from the time they hatch.
If all that, plus behaviors such as hiding among seagrasses, driftwood, corals and rocks, doesn’t help them evade tuna, marlins and sharks, bigfin reef squids can jet away in a cloud of ink that temporarily blinds a pursuing predator.
Grow fast, spawn and die young
Bigfins are a wide-ranging Indo-Pacific species: They’re found from Japan to Australia and New Zealand, and from Hawaii to the eastern coast of Africa from Madagascar up to the Red Sea. Following the construction of Egypt’s Suez Canal in the mid-19th century, bigfins also found their way into the Mediterranean Sea, similar to how sea lampreys entered the Great Lakes thanks to the Welland Canal.
The squids arrived at Shedd in mid-July as eggs, acquired from a sustainably managed source in Japan. Encased in gelatinous capsules, the eggs were tenderly incubated for about three weeks. Once they hatched, the bigfins started eating and growing bigtime.
These squids can consume up to 30 percent of their body weight daily, and they have the fastest recorded growth rate of any large marine invertebrate. The squidlets were roughly the size of a grain of rice when they hatched. At 2 weeks, they were a half-inch long; at 7 weeks, they were 4 to 6 inches long. On their four-times-a-day meals of increasing larger fish or crustaceans, they’re now 8 to 10 inches long (males are larger).
Like a lot of other cephalopods, bigfins have short life spans—a maximum of 11 months—dictated by their spawn-and-die life cycle. As Shedd’s squids reached full size, aquarists began to see reproductive behavior: males flashing characteristic breeding colors and patterns and receptive females responding with their own chromatic communication. While aquarists did not witness mating, a nocturnal ritual during which the male passes a sperm packet along a specialized arm into the female’s mantle cavity, they could see when the fertilized eggs began developing inside the females.
In anticipation, Shedd’s aquarists hung fabricated egg capsules in a rock crevice in the center of the habitat to attract females to do the same. Female squids use a common area to lay their eggs.
Instead of the rocks, the females chose a towering strand of artificial kelp toward a back corner of the exhibit and began laying around noon on Jan. 26. Within two hours, at least half a dozen large clusters of egg capsules, looking like bunches of long white grapes, hung along the length of the kelp strand. Females continued to add to the masses, depositing one egg capsule at a time from under their mantles.
Males and females can mate multiple times, and females can lay several rounds of egg capsules. Parental involvement ends with egg laying. Their jobs done, the squids do not survive more than two months beyond the spawning season.
Applying what they learned from the successful rearing of this squid group, aquarists will gingerly transfer the eggs to a quarantine area and incubate them. Within two to three weeks of the laying date, they hope to have the start of a sustainable bigfin reef squid population. But they advise that there would be a gap of several months between the time the current group naturally expires and a new generation of squids would be developed enough to go on exhibit.
Some good things come in small, amazing, color-changing packages that don’t stick around long. Plan your visit to see the bigfin reef squids soon!
—Karen Furnweger, web editor
Read more about Shedd’s other cephalopods:
Dinner Dance with a Nautilus
The Well-mannered Octopus, Part 1 and Part 2
International Cephalopod Awareness Days: Foyer Floor Fossils