水すい生せい生せい物ぶつ

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Meanings

aquatic life; water creatures

General term for organisms living in water, including fish, aquatic plants, and microorganisms.

海かい洋よう生せい物ぶつ
海洋生物 specifically refers to marine organisms, while 水生生物 includes all aquatic life, both freshwater and saltwater.
淡たん水すい生せい物ぶつ
淡水生物 means freshwater organisms, a subset of 水生生物.

水すい生せい生せい物ぶつ
Standard kanji spelling; 水生 means 'aquatic' and 生物 means 'organism'.
水すい棲せい生せい物ぶつ
Alternate spelling using 棲 (dwell) instead of 生 (life); both are used, but 水生生物 is more common.

Compound of 水生 (aquatic) + 生物 (organism). The spelling 水棲生物 uses 棲 (dwell) to emphasize living in water, but both forms are transparent.