Meet Smenispa irregularis, one of more than 100 different species of crustacean isopods found lurking in the mouths of fishes.

Fish tongue biters (parasitic crustacean isopod of the family Cymothoidae) were discovered in the 1700s and first named by Linnaeus (1775), but have recently gained much publicity from Brusca and Gilligan’s (1983) description of Cymothoa exigua as a tongue-replacing isopod from the eastern Pacific.

Since then, internet blogs, YouTube and other videos have generally incorrectly defined most tongue biters as Cymothoa exigua. But there’s far more than just one species of cymothoid species worldwide.

The Cymothoidae is a large family, with 383 species in 40 genera. They are parasites and occur on a great diversity of host fishes worldwide, generally displaying high fish host specificity (that is, one species of cymothoid prefers certain species of fish). Cymothoids are also site specific on their host, meaning they are found at particular places such as near the gills, mouth, burrowed inside the flesh, and near the eyes/face or caudal fins.

There are eight genera of mouth-attaching cymothoid, with approximately 100 species found worldwide. The most speciose genera are Cymothoa and Ceratothoa. However, much of the taxonomy, biology, host specificity and distribution of the mouth-attaching cymothoids remain unclear. The aim of my research is to review the morphology and to redescribe the buccal (mouth)-attaching cymothoids from Australian waters.

One example of a little known Australian cymothoid is the small mouth-attaching genus Smenispa (previously Enispa) that occurs in the tropics and subtropics. Only two species are known worldwide, with few records since its original description in 1884. One of the species is Smenispa irregularis from the Indian Ocean, with two records from Australia. Our current research shows that Smenispa irregularis occurs on three fish families [Sparidae (sea breams); Carangidae (jacks mackerels, pompanos, scads); and Psettodidae (spiny turbots)], suggesting the species has low host-specificity (apparently it’s not as picky as some). Smenispa irregularis was in historic times incorrectly placed in the genus Cymothoa because of its variable appearance and similarity to other mouth-attaching cymothoids.

To prevent future confusion and misidentification, I undertook the highly exacting, demanding, challenging and precise work surrounding taxonomy, where minute details of the appendages (such as the antenna, mouthparts and tail) are taken into consideration to unambiguously define the species. The availability of many specimens for each particular species was also very important, enabling me to take into account the degree of variation within a species and better justify the important characters that differentiates one species from another.

My research may have important ecological and economical implications. For example, understanding the diversity of tongue biters, and being able to accurately identify species, is important in the aquaculture industry. In particular, some cymothoids may be capable of parasitising aquaculture fishes which are not their natural host due to wild fishes feeding near aquaculture pens. As some fishes are known for their vast migrations, the problems may be global in scale.

So the next time you get hold of a tongue-biter and are keen to know if you have discovered a new species or a species new to Australian waters, contact a museum curator in your state. Who knows, you may just get lucky and get a parasite named after you!

Melissa Beata Martin
PhD candidate
National Centre for Marine Conservation and Resource Sustainability
Australian Maritime College/ University of Tasmania


More information:
Melissa Martin is under the supervision of Dr Niel Bruce and Prof. Barbara Nowak. In 2012, she received a Geddes Postgraduate Fellowship to visit the Australian Museum and work on Tongue biters. 

Brusca, RC & Gilligan, MR (1983). Tongue replacement in a marine fish (Lutjanus guttatus) by a parasitic isopod (Crustacea: Isopoda). Copeia, 3, 813–16.

Martin, MB; Bruce, NL & Nowak, BF (2014) Smenispa irregularis (Bleeker, 1857) (Crustacea: Isopoda: Cymothoidae), a buccal-attaching fish parasite from Australia. Records of the Australian Museum, 66, 233- 240.