fisshu means "Fish" in English.
It's a katakanization, a loan-word.

  • sakana is the common term for fish, while gyorui is the technical term for the animals that are fish.
fisshu is normally written with katakana, as フィッシュ.
fisshu written with hiragana is ふぃっしゅ.
fisshu does not have kanji.
Romaji fi sshu

Orthography Notes

  • フィ and シュ are compound kana representing a single syllable with multiple characters.
  • ッシュ contains a small tsu which makes the consonant of the syllable longer.

Further Reading

Wikipedia: (Fish)