Middle Primitive Elvish
liñwi
noun. fish
liw
root. *fish
skala
noun. fish
There are more words but they are from Tolkien's earlier conceptional periods. Tolkien likely changed these words as he evolved the aesthetics and completeness of the languages. You may even find languages that Tolkien later rejected. Do not mix words from different time periods unless you are familiar with the phonetic developments.
Below: Tolkien's Late Period (1950–1973). These are from Tolkien's late conceptual period — his most settled forms of the languages. Prefer these over the earlier ones above when composing new text.
An unglossed root in The Etymologies of the 1930s whose derivatives had to do with fish, such as ᴹQ. lingwe and N. lhim “fish” (Ety/LIW). Q. lingwi “fish” appeared in some 1965 notes (NM/336), indicating the ongoing validity of √LIW. √LIW is probably a later iteration of ᴱ√IWI from the Qenya Lexicon of the 1910s that likewise was the basis for fish-words from this period, such as ᴱQ. ingwe and G. ing (QL/43; GL/51). The root ᴹ√IW also appeared in The Etymologies (EtyAC/IW), but was unglossed and had no derivatives, so it isn’t clear what Tolkien intended this root to mean in the 1930s, and it may well have been abandoned.