How to Say "Guinea Pig" in Japanese

モルモット

morumotto[mo̞ɾɯ̟mo̞t̚to̞]

The English phrase "guinea pig" can be translated into Japanese as モルモット (morumotto).

The term モルモット is used to refer to an experimental subject (noun).

Meaning: experimental subject (noun)

Is there a formal and an informal way to say it?

モルモット is considered an informal way to say "guinea pig" in Japanese.

morumotto

The Japanese name for this animal, モルモット, actually refers to a completely different species: the marmot. This happened because Dutch traders in the 19th century mistakenly identified the creature when they first introduced it to Japan.
In Japanese pop culture and anime, referring to a character as a モルモット often implies they are being manipulated or toyed with by a mastermind, rather than just participating in a scientific study.
While モルモット is the common term for the animal, the formal scientific term for a guinea pig in Japanese is テンジクネズミ, which literally means 'India mouse'.

モルモットを飼ってるんだ。
I have a guinea pig.
This sentence demonstrates the use of モルモット when stating that you own a guinea pig.
Tatoeba #9069227 by small_snow, translation #8155347 by CM
サミはモルモットを飼ってるんだよ。
Sami has a guinea pig.
This sentence shows how to use モルモット when talking about someone else owning one.
Tatoeba #9069242 by small_snow, translation #7183430 by OsoHombre
メアリーはクリスマスにモルモットをもらったんだよ。
Mary got a Guinea pig for Christmas.
This sentence illustrates the use of モルモット when describing receiving a guinea pig as a gift.
Tatoeba #9069225 by small_snow, translation #3711871 by Hybrid
うちには可愛いモルモットがいます。
We have a cute guinea pig at home.
友達の家でムースという名前のモルモットを見ました。
I saw a guinea pig named Moose at my friend's house.
2 more sentences on Tatoeba

Misaki and Yota are discussing a new software update at school.

美咲 Misaki

新機能のモルモットになっちゃった。
Shinkinou no morumotto ni natchatta.
I became a guinea pig for the new features.
陽太 Yota

使いづらいところはある？
Tsukaizurai tokoro wa aru?
Is there anything difficult to use?
美咲 Misaki

ボタンがすごく押しにくいよ。
Botan ga sugoku oshinikui yo.
The buttons are very hard to press.
陽太 Yota

それは困ったね。
Sore wa komatta ne.
That is a problem.

Sources

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