The sea lice (Anilocra physodes) are parasitic crustaceans of cymothoidae family. These isopods are characterized by parasitizing a wide variety of fish species, being able to be located on the external surfaces between the scales, in the oral cavity and in the gill cavities.
Despite being parasitic organisms, they have undergone few notable body modifications. The only truly distinctive body modification focuses on the ends of most of the legs, which have been transformed into formidable grappling hooks for attachment.
Anilocra physodes By Parent Géry
The hooks of the first pair of legs are directed in such a way as to prevent these crustaceans from shedding despite the movements of the fish, the speed of their movement and their erratic movements.
Various groups of species have been established based on shared characteristics, such as body shape, legs, and anténules. However, there is no phylogenetic evidence to validate them.
Reproduction
Female Anilocra physodes are permanently sessile and always attach to a host species of fish.
On the other hand, males are free-living, so reproduction depends on the encounter of a swimming male with a female attached to a fish. Once the reproductive event occurs, the eggs hatch directly into a speckled larva.
Once the male fertilizes the female through two gonopores present at the base of the pereiopods of the sixth segment of the pereion, the eggs are transferred to large plate-shaped lamellae or oostegites. These lamellae project on the bases of the anterior pereiopods, covering almost the entire ventral surface of the female.
This species of pouch protects the eggs until they develop into “speckled” larvae that are then released into the surrounding water. This developmental period can extend for about three weeks before hatching.
These larvae have characteristics very similar to those of the adults, however, they lack the last pair of pereiopods and are smaller in size.
The larvae of A. physodes are photopositive, so they move in the direction of the areas with the greatest availability of light.
Nutrition
The sea lice feed exclusively on the host's blood. Once attached to the fish, A. physodes sucks the blood thanks to its modified mouthpart for piercing. This species, due to its habits, may be involved in the transmission of some protozoa to the host.
The parasitism of this species extends to a great diversity of hosts, including more than 57 species of bony fish Actinopterygii and cartilaginous fish Elasmobranchii.
The most commonly parasitized families are Sparidae, Carangidae, Mugilidae, Centrachantidae, Sciaenidae, Mullidae, Scorpaenidae and 25 other families to a lesser extent.
Fish parasitized by Anilocra physodes By Parent Géry
Several species of fish are parasitized by this small crustacean. These include: Spicara smaris, S. maena, Scomber japonicum, Sparus auratus, Dicentrachus labrax, Boops boops, Diplodus annularis, D. vulgaris, D. sargus, Pagellus erythrinus, Spondyliosoma cantharus, and Oblado melanura.
All these observations come from the Aegean Sea and the Black Sea. On the other hand, this parasitic crustacean has also been recorded perching in some species of cephalopods in the western Mediterranean.
Parasitized fish generally carry a single individual of these crustaceans. In several cases the presence of a male and a female fixed on the lateral-caudal surface is reported, probably reproducing.
Natural predators
These crustaceans are also part of the diet of several species of fish. For example, Hoplostethus mediterraneus a benthopelagic fish that feeds mainly on crustaceans such as Meganyctiphanes norvegica and A. physodes.
Several deep-sea species of the Aegean Sea also frequently consume these small crustaceans.
Other species of bony fish frequently catch A. physodes when they are free and in search of a host. The larvae are frequent prey for fish species that feed on the surface of the water.
Some species of cleaner fish or specialized in feeding on ectoparasites are capable of removing these isopods from other fish. Healthy fish with high mobility that are parasitized can get rid of the parasite by rubbing the affected surface against the bottom or some coral to later ingest it.
References
- Innal, D., Kirkim, F., & Erk akan, F. (2007). The parasitic isopods, Anilocra frontalis and Anilocra physodes (Crustacea; Isopoda) on some marine fish in Antalya Gulf, Turkey. Bulletin-European Association of Fish Pathologists, 27 (6), 239.
- Kearn, GC (2005). Leeches, lice and lampreys: a natural history of skin and gill parasites of fishes. Springer Science & Business Media.
- Körner, HK (1982). Countershading by physiological color change in the fish louse Anilocra physodes L. (Crustacea: Isopoda). Oecology, 55 (2), 248-250.
- Narvaez P, Barreiros JP and Soares MC. 2015. The parasitic isopod Anilocra physodes, as a novel food source for the lizardfish Synodus saurus (Synodontidae). Cybium, 39 (4): 313-314.
- Öktener, A., Torcu-Koç, H., Erdoğan, Z., & Trilles, JP (2010). Scuba diving photography: A useful method for taxonomic and ecologic studies on fish parasites (Cymothoidae). Journal of Marine Animals and Their Ecology, 3 (2), 3-9.
- Öktener, A., Alaş, A., & Türker, D. (2018). First Record of Anilocra physodes (Isopoda, Cymothoidae) on the Phycis blennoides (Pisces; Phycidae) with morphological characters and hosts preferences. Jordan Journal of Biological Sciences, 11 (1).
- Pais, C. (2002). Diet of a deep-sea fish, Hoplostethus mediterraneus, from the south coast of Portugal. Journal of the Marine Biological Association of the United Kingdom, 82 (2), 351-352.
- Trilles JP. 1977. Les Cymothoidae (Isopoda, Flabellifera) parasites des poissons du Rijksmuseum van Natuurlijke Historie de Leiden. Méditerranée et Atlantique Nord-Oriental. Zool Med Leiden, 52: 7-17.