It is the causative agent of various pathologies including tissue damage at the parasitisation site (tongue), growth defects, decrease in mean host weight and size and increases mortalities in farmed and wild fish populations.

[2]  It has been recorded in six different fish families: Sparidae (Boops boops, Diplodus annularis, Pagelus erythrinus, Spicara smaris, Sparus aurata), Carangidae (Trachurus mediterraneus), Clupeidae (Sardina pilchardus), Maenidae, Scorpenidae (Scorpaena notata, Scorpaena porcus), and Mugilidae (Liza aurata).

C. oestroides is one of the most devastating ectoparasites in Mediterranean aquaculture, with an unequal distribution along different geographical areas[5][6][7][8] The life cycle of Cymothoidae, which are protandric hermaphrodites,[9] encompasses mating of adult male and female in the host buccal cavity, development of embryos in the female marsupium followed by moulting through pullus stages (I–IV stages).

The parasite attaches on the host body (flanks, fins), and then crawls towards the operculum, where it enters the buccal cavity and settles on the base of the tongue.

[citation needed] This parasite causes various pathologies, including tissue damage of the tongue, growth defects, anaemia, decrease in mean host weight and size and increased mortalities in farmed and wild fish populations.

Athanassopoulou et al. (1999)[12] noticed that Ceratothoa-infected fish are also infected with Rickettsia-like organisms (RLO), and related the latter pathogen to transmission by the isopod.

Vagianou et al. (2006)[7] observed that larval stages of C. oestroides (pulli II) that attack small fish induce the most damage, causing severe ulcers and extensive granulomatous lesions in the eyes that lead to blindness or the total loss of the eyeball.

[citation needed] Treatment of isopod infestations on young fish has been attempted with success by means of hourly formalin baths and manual removing from the buccal cavity during the vaccination for other diseases.