Spotlight on Vet Medicine
June 29, 2007
Let There Be Sight: Treating a Cuttlefish’s Eye
Cuttlefish rely on great vision, so treating a Zoo cuttlefish’s eye problems was a priority for veterinarians.
Creatures of the Mediterranean Sea and the Atlantic Ocean from the English Channel to the tip of southern Africa, common cuttlefish (Sepia officinalis) are best known in their native range as staples of some coastal peoples’ seafood fare.
Among scientists, however, they are famed for their intelligence—by some accounts, the most intelligent of all invertebrates—their ability to change color in a flash to hide or to signal other cuttlefish or predators, and their remarkable eyes.
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| The 120 or so species of cuttlefish are among the about 700 species of cephalopods, a specialized group of marine mollusks that includes octopus, squid, and nautilus. The Zoo exhibits common cuttlefish. |
A carnivorous predator, the common cuttlefish spends much of its time on the seabed, leaving mostly to hunt for their next meal of small mollusks—including smaller cuttlefish—shrimp, and crab. Sometime a cuttlefish uncovers prey hiding in the seabed by blowing water to shoo away the sand. It uses its two tentacles to seize prey, and its eight arms to manipulate it. Before chowing down, a cuttlefish paralyzes the prey with an injection of venomous saliva, or simply crushes it in its strong, parrot-like beak.
Many species prey on cuttlefish as well, including dolphins, sharks, seals, and fish. Cuttlefish respond to a looming threat by secreting a cloud of ink that confuses the predator and obscures the cuttlefish’s escape. Until recently, people used the sepia-colored ink as a dye.
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| A cuttlefish's W-shaped pupil. |
Although cuttlefish are colorblind, seeing the world in black and white and shades of gray, they have superb vision and their large eyes are structurally similar to ours, with a cornea, retina, iris, and pupil. The eyes work about the same too, although cuttlefish focus by re-shaping the entire eye to move the lens while we reshape the lens. Another difference is the curving W-shaped pupil.
Common cuttlefish have long been residents of the Zoo’s Invertebrates exhibit. Recently, keepers noticed that one eye of an 11-month-old cuttlefish was cloudy. A veterinary exam revealed small cataracts in both eyes and inflammation of the right cornea. Eye lesions like these may be due to infections, trauma, metabolic diseases, or primary eye diseases such as glaucoma. But the most likely cause of the corneal inflammation was a bacterial infection, so vets started the cuttlefish on an antibiotic.
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| To medicate a cuttlefish, keepers inject the dose into a shrimp, which is then fed to the cuttlefish. |
They prescribed long-term treatment with enrofloxacin, an antibiotic that effectively treats many of the bacteria that cause eye infections. Keepers gave the animal its twice-a-day dose by injecting the drug into a shrimp before feeding the shrimp to the cuttlefish. The medication relieved the corneal inflammation within days. The cuttlefish’s cataracts are still present but are considered mild; the cuttlefish retains good vision.
Three months later, there has not been a recurrence of the corneal inflammation. The cuttlefish is active and has a good appetite. In fact, this animal recently celebrated its 14-month birthday—and that’s old for cuttlefish, which generally live only about a year and at most about two years, in zoos and in the wild.
Visit cuttlefish in Invertebrates.
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