by Piter Kehoma Boll
We all know that crustaceans comprise the most morphologically and ecologically diverse group of arthropods. One peculiar clade is that of the arguloids or fish lice.
As you may infer from the common name, the fish lice are parasites of fish, and eventually other vertebrates. One of the most common an well-known species is Argulus foliaceus, known as the common fish louse.
The common fish louse is found in freshwater bodies of Europe and parasitizes many different fish species. Their only food is fish blood, so they are forced to look for a host as soon as they hatch from their eggs. Once they find a fish, they attach firmly to its skin and remain there for most of their life. They only leave the host to mate or if the host dies and they need to find a new one. Trouts, perches, roaches and sticklebacks are some common hosts of the common fish louse.
The first and only larval stage, called metanauplius, measures less than 1 mm in length and has long and plumose antennae and palps but relatively short legs. The thoracic legs have claws, though, and help them to attach to the host. In the second stage, already a young adult, the antennae became much shorter but the legs grow more, especially the abdominal legs, which became plumose like the antennae used to be. From there on, the body remains with a more or less constant shape but increases in size, reaching about 6 mm at the 11th stage.
In natural environments, the number of common fish lice per fish is usually small and they do not harm the host that much. However, in confined habitats, such as fish farms, they can reach high densities and end up causing a high fish mortality.
Just like many other external parasites or other types of blood-sucking animals, the common fish louse can serve as an intermediary host for some nematode parasites that infect freshwater fish. The larval stages of the worm reach the fish louse when he feeds on infected fish and remain in its body, eventually infecting a new fish when the crustacean abandons its current home and searches for another one.
Thus, sometimes the main problem that fish face is not the fish louse itself, but rather its hitchhikers.
– – –
Friday Fellow: Glacial calanus (on 1 July 2016)
Friday Fellow: Common Goose Barnacle (on 31 May 2019)
– – –
Harrison AJ, Gault NFS, Dick JTA (2006) Seasonal and vertical patterns of egg-laying by the freshwater fish louse Argulus foliaceus (Crustacea: Branchiura). Diseases of Aquatic Organisms 68:167–173.
Molnár K, Székely C (1998) Occurrence of skrjabillanid nematodes in fishes of Hungary and in the intermediate host, Argulus foliaceus. Acta Veterinaria Hungarica 46(4): 451-463.
Pasternak AF, Mikheev VN, Valtonen ET (2000) Life history charactheristics of Argulus foliaceus L. (Crustacea: Branchiura) populations in Central Finland. Annales Zoologici Fennici 37: 25–35.
Rushton-Mellor SK, Boxshall GA (1994) The developmental sequence of Argulus foliaceus (Crustacea: Branchiura). Journal of Natural History 28(4): 763–785. doi: 10.1080/00222939400770391
– – –
* This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.