Lernaea cyprinacea

Preferred Scientific Name

• Lernaea cyprinacea Linnaeus

• Domain: Eukaryota
•     Kingdom: Metazoa
•         Phylum: Arthropoda
•             Subphylum: Crustacea
•                 Class: Copepoda
•                     Order: Cyclopoida
•                         Family: Lernaeidae
•                             Genus: Lernaea
•                                 Species: Lernaea cyprinacea

anchor worm disease

Morphology and life cycle

The adult female Lernaea cyprinacea has a small semispherical cephalothorax, which contains the mouth. Behind it is a well-developed holdfast, normally consisting of two bifurcate dorsal processes and two simple ventral processes (Fig. 6A). The elongate neck and trunk carry the four pairs of legs of the premetamorphosed female. The abdomen is short. In situ, the holdfast and part of the trunk are buried in the host while most of the trunk and the abdomen project into the water (Fig. 7).

Fig. 6. Lernaea spp. morphology of female. A and B. L. cyprinacea. C. L. polymorpha. D. L. cruciata.

Fig. 7. Lernaea cyprinacea. Diagram of adult female in situ.

L. cyprinacea has three free-living naupliar stages and five copepodid stages. The naupliar stages are non-feeding and moult to infective copepodids in about 4 days. Copepodids are usually on the gills and are relatively immobile, although they are not permanently attached. Copepodids finally moult to free-moving adult males or premetamorphosed females in 7+ days, depending on temperature (Shields, 1978; Shariff and Sommerville, 1986b). Adult males die within 24 h. Females are fertilized and either attack the same host or swim to another host, where they chew and bore their way into the host tissues as they metamorphose into adults. Within 1 day, before they have fully metamorphosed, they produce their first batch of eggs. These hatch 24 to 36 h later and the egg sacs are then shed. A new pair of egg sacs is produced within 1 to 3 days (Shields and Goode, 1978; Shariff and Sommerville, 1986b). The largest egg sacs are produced 5 to 10 days postmetamorphosis and the parasites die within 30 days at 28-32°C.

Development is greatly reduced at lower temperatures; at 20°C nauplii take 7 days to moult into copepodids and they cease development altogether below this temperature. Shields and Tidd (1968) found that some metamorphosed females survived at 10°C for over 3 months and grew slowly, though many were lost from the fish. Others were lost when the temperature was raised to 25°C, possibly because they had not burrowed deeply enough during the cold period. Of 71, only six survived to produce eggs. Nevertheless, in cold temperate climates, the parasites probably overwinter as metamorphosed females.

L. cyprinacea requires only one host to complete its life cycle, usually a cyprinid, though adult females have been found on many species of fish and copepodids also have relatively low host specificity. Copepodids have been found on the gills of other fishes, such as African catfish Bagrus spp., and even in the branchial chamber of tadpoles, Rana spp. (Fryer, 1966; Shields and Tidd, 1974). In a polyculture system in southern USA, channel catfish, Ictalurus punctatus, had eight to 50 copepodids on the surface of each gill filament and small numbers of adult females on the skin, whereas thousands of adult females were on the skin of cohabiting big-head carp Aristichthys nobilis (Goodwin, 1999).