Lethacotyle fijiensis is a species of monogeneans of the family Protomicrocotylidae.

The species is ectoparasitic on the gills of an unknown carangid fish identified in the original publication[1] as "yellow jack".

[2] Lethacotyle fijiensis has been found only off Fiji by Manter & Prince in 1953[1] (the material of the original description, hence the Latin species name, fijiensis, meaning "from Fiji") and allegedly off Andaman Islands by Ramalingam in 1968,[3][4] although other authors[2] have expressed doubt that the later author actually found the same species.

[1] The body is elongate, flat, there are numerous testes and a single ovary.

It bears a terminal lappet which is striated, and there are no clamps - this is a characteristic of the genus Lethacotyle.