Manatees have thousands of taste cells — and apparently don't care [Huam-dong Paper Lab]

An animal that looks like a cow but cannot distinguish sweet from bitter at all — that is the Caribbean manatee. The finding runs directly counter to the long-held assumption that manatees, as one of the few herbivores living in the sea, would have developed a particularly keen sense of taste.

A joint research team from Linköping University in Sweden and ECOSUR in Mexico recently published the findings in the international journal Physiology & Behavior.

Most marine animals, such as whales and seals, have largely lost their sense of taste. Because they swallow prey whole without chewing, there is little need to distinguish flavors, and the relevant genes have been deactivated over time. Whales, for instance, are known to perceive only saltiness.

The "sea cow" manatee is different. It is the only animal that lives in the sea yet feeds exclusively on plants. Its genes for detecting sweetness and umami remain fully intact, and seven genes for detecting bitterness are still active. The tongue contains an average of more than 11,000 taste receptor cells — comparable to cattle and rabbits. Researchers had therefore assumed that manatees use taste to screen out toxic plants and seek out palatable ones.

The research team tested the taste responses of three manatees living at an aquarium in Mexico.

The method involved presenting each animal with two baby-bottle-style containers held side by side — one filled with water flavored with sweet, salty, sour, umami, or bitter compounds, and the other with plain seawater. The researchers observed which container each manatee drank from more over a two-minute period.

The results were unexpected. None of the three manatees showed a preference for either container. Doubling the concentration of the flavored solution made no difference, nor did replacing the seawater with fresh water. Even at concentrations that most animals would readily detect, the manatees showed no response.

Manatees are known to seek out fresh water, so researchers expected them to prefer it over saltwater. Again, the results told a different story: all three animals drank fresh water and seawater in equal measure.

The research team traced this indifference to the manatee's unusual diet. The aquatic plants manatees eat are 80 to 90 percent water, meaning the animals take in enough moisture through food alone without needing to seek out drinking water separately. Manatees can also produce water metabolically by burning stored body fat. With hydration needs easily met, there is simply no need to distinguish water by taste.

The team said that having intact taste receptor cells or taste genes does not necessarily mean an animal tastes well. Even among humans, so-called "supertasters" — those with an unusually high number of such cells — tend to be sensitive mainly to bitterness, not to other flavors.

Wild manatees are known to avoid astringent plants.

In an earlier separate study, one manatee was offered 54 plant species and ate only 27 — all varieties it had previously been observed to favor.

However, the research team said it remains unclear whether manatees avoid certain plants because of their astringent taste. Familiarity, rather than flavor, may play a greater role in food selection. The team also noted uncertainty about whether astringency registers as bitterness on the tongue or as a separate physical sensation — the puckering feeling in the mouth.

The team acknowledged the limitations of the experimental approach, noting that a lack of behavioral response does not necessarily mean the animals cannot taste at all.

"Contrary to the common assumption that an exclusively herbivorous diet would preserve taste sensitivity, manatees may be experiencing a decline in taste function similar to other marine animals," the team said. However, it added, "whether manatees genuinely cannot taste, or simply do not act on what they taste, could not be determined from this study."

DOI: 10.1016/j.physbeh.2026.115312

Astrée Calloch, Yann Henaut, Matthias Laska, "Can't taste, or don't care? Greater Caribbean manatees (Trichechus manatus manatus) fail to display preferences for or aversions to the five basic taste qualities," Physiology & Behavior, June 2026.