Plural of “aquarium”

The plural of aquarium is aquariums (some dictionaries also accept aquaria).

Why

"Aquarium" is a modern coinage, not an inherited classical word — it was built in the 19th century from Latin "aqua" (water) plus the suffix "-arium," meaning "a place for," on the model of the genuinely ancient Latin word "vivarium" (a place for keeping live animals). Because "aquarium" was never actually a word in classical Latin, there's no true inherited Latin plural to defer to, only a plural constructed by analogy once the word existed in English.

That modern, invented status is exactly why "aquariums" is overwhelmingly the standard plural: with no genuine classical precedent to preserve, English speakers simply applied the regular pattern to a new coinage from the start. "Aquaria" does show up occasionally, mostly among people who assume any -um noun should take an -a plural by analogy with words like "stadium" or "museum," but it was never dominant and remains a distinct minority form.

Usage note

"Aquariums" is correct in every context, from a home hobbyist's fish tanks to large public aquarium institutions; there's no register, technical or otherwise, in which "aquaria" is expected or preferred.

Large public aquariums today function as much as conservation and research institutions as they do as tourist attractions, running breeding programs for endangered marine species and funding field research far from the tanks visitors actually see — a mission considerably more ambitious than Gosse's original Victorian parlor tanks ever anticipated.

Common real mistakes

The main slip is assuming that because "aquarium" ends in -um it must follow the same pattern as "stadium" or "museum" and take an -a plural — a reasonable-looking but ultimately mistaken analogy, since those other words have genuine classical Latin histories that "aquarium," as a 19th-century invention, simply doesn't share. Writers should also avoid calling a simple fishbowl an "aquarium," since the word generally implies a larger, more deliberately maintained ecosystem rather than a single small bowl.

The wider pattern

"Aquarium" belongs to a small set of modern scientific coinages built from Latin roots but invented well after Latin itself was a living language — "solarium" and "terrarium" work the same way, each pluralizing with a plain English -s because there was never a real ancient Latin plural to inherit in the first place. The word's coiner, the English naturalist Philip Henry Gosse, popularized "aquarium" in the 1850s specifically to describe glass tanks for observing marine life at home, a Victorian fashion that spread quickly once affordable glass and reliable water pumps made keeping fish indoors practical for ordinary households rather than only wealthy collectors.

Examples

• The city built a new public aquarium along the waterfront.
• She keeps three separate aquariums for different species of fish.
• Several large aquariums around the country host overnight programs for kids.
• The aquarium's main tank holds over a million gallons of water.
• He set up two small aquariums in his classroom.
• The pair of aquariums downtown merged into a single larger institution.
• Public aquariums play a growing role in marine conservation research.
• Home aquariums require regular water testing to stay healthy.
• The exhibit compared aquariums from five different countries.
• Visitors can tour both aquariums with a single combined ticket.
• Victorian naturalist Philip Henry Gosse helped popularize home aquariums in the 1850s.
• The two aquariums downtown jointly run a shark conservation program.
• School field trips to the aquariums are booked months in advance.
• Several public aquariums now run active breeding programs for endangered species.
• The new aquarium exhibit recreates a deep-sea coral reef environment.
• The children pressed their faces against the glass of the largest aquarium tank.
• Marine biologists occasionally borrow specimens between aquariums for joint research projects.
• The two aquariums split visiting hours during the busiest holiday weekends.
• The aquarium extended its hours during the summer tourist season.