A variety of problems is caused by parasites in larger organisms which may lie inside or outside of the body during its life cycle (Llewellyn et al., 2014).
The major groups of ectoparasites are Arthropods (crustaceans), Platyhelminthes (monogenesis), and Protozoans. The protozoans are mostly commensal on fish bodies and free living. Most of it causes harmful diseases and is lethal for the host. Ciliates are one of the most common ectoparasites (Buchmann et al., 2001).
Lernaea are the copepod parasite which is known as an Anchor worm which may cause infestation and death in a variety of freshwater fish fauna. It may infect the wild species as well as the pond fish. The favorable conditions for the infestation of Lernaea species are the summer season and slow-moving water (stagnant water body). About 110 (hundred and ten) species of the parasite (Lernaea or similar to Lernaea) have been explored up to now. The Lernaea cyprinacea are members of Lernaeid which are found throughout the world. The parasite is common in Cyprinids goldfish, grass carp, and common carp. It can infect the catfish which are mostly stocked in ponds with bighead carp. The Lernaea is the crustacean and copepod that also infects shrimp, crabs, and lobsters in various stages of its life cycles, unlike other free-living copepod species which may not cause disease in the host. The parasites of this group have a complex life cycle, the individual of the group is not passed by the help of an intermediate host organism; whereas it can spread directly from one fish body to the other. The organism needs only a single fish (a member of the class amphibian) to develop from an egg to an adult. The total life cycle of the parasite is completed in 18 to 25 days (Robert et al., 2001).
The host is the fish which are infected by the parasites. Some parasites have suckers for attachment to the host body while the rest of them lay eggs. It can modify its immunity and biochemistry according to the situation, and cannot be killed or digested. The economic losses occur in the Fisheries sector of Pakistan due to infection of Lernaea species, monogenic species, Argulus species, and Dactylogyrus species (Daulat et al., 1976).
Productivity and fish health are affected by parasites among the ectoparasites. The fish migration and behavior patterns are affected by parasitism. The community structure, survival value, and reproduction of the host are negatively affected by the parasites (Luque and Poulin 2008). Some of the parasites become pathogenic and lethal for fingerlings and fry while most of them show commensalism (Demopoulos et al., 2015).
Lernea Cyperaceae Linnaeus is an introduced fish parasite that can cause mortality in various habitats including fish hatcheries and ponds, the species can mostly affect high-density areas with higher temperatures (zman and Rayner 1958). The parasite Laernaea cyprineace is most abundant and harmful among the members of the family Larnaea. (Bilal et al., 2021). The Lernaeid are the fish parasites that belong to the main group of Crustacea (Copepoda). An extensive morphological fitness (adaptation) is shown by the Lernnaeidae family of cyclopoids which keeps them a little bit distinct from the members of the genus Cyclops and others (Ozel et al .,2014).
The parasite was first found in Asia later it may be shifted to another continent of the world with farm fish (Innal and Avenant, 2012). The parasite is recorded from various regions of the world including Asia, Southern Africa, Australia, Europe, and its adjacent areas (Hoffman, 2019). The Lernaea cyprinacea is found in Nurseries, brood stocks water hatcheries, and fish ponds of Jessore regions. The parasite (Lernaea cyprinacea) may infect perches, catfish, Minor barbs, and major carps (both Chinese and Indian carps) (Hossain et al., 2018).
A diverse habitat is occupied by individuals of the family Lernaeidae, parasites are found in marine and freshwater. The family is represented by fourteen (14) genera with one hundred and ten (110) species (Ho, 1998). The parasites are more in number in the aquatic ecosystem and survive with their host in a dynamic equilibrium (Marcogliese, et al., 2011).
Human health is directly or indirectly affected by infectious. The allergic reaction is caused by either pathogen or living parasites present in the tissues of fish bodies (Buchmann et al., 2001).
The adult member of Lernaea cyprinacea attached to the skins and muscles of the host leaves an opening to enter the secondary microbe and cause death to the infected fish (Van Duijn et al., 1973).
The pathogenicity of lernaeids largely depends on the size of their host and attachment site preferences. Aggregated infections of the mouth and lips occur in Barbus altianalis with Lernaea barinmiana and in cichlids by Lernaea cyprinacea, fin infections caused by Lernaea lophiara in cichlids (Fryer, 1968; Paperna, 1996). Fish with large numbers of parasites will be thin and their body color becomes darkened, also extensive abrasions appear with loosing and sloughing on its skin. Severe destruction of the gills occurs as well as losses and mortalities up to 50% (Eissa et al., 2004).
The life cycle of the parasite Lernaea has nine stages, out of which three stages are free-living naupliar, five copepodid, and one stage of an adult. During the fourth stage, copulation of both adult males and females occurs at the first host. When the copulation insures the male is dyed whereas the female metamorphoses and enters the anterior tissues of the host body, laying eggs (Nagasawa et al., 2007).
A tremendous modification in cephalothorax has been shown by the adult female of the genus Lernaea. The body is vermiform and elongated, and the mouth of the parasite female is much reduced. The head is changed into 4 horn shaped compartments which are now cylindrical and long, the anterior appendages are simple while the two posterior ones are bifurcated. The parasites use the horns for attachment to the host body and it’s buried under the epidermis. The abdomen is bent toward the dorsal and short in length. The egg sacs protrude beyond the body while the genital pore is present near the posterior end of the body. The immature forms of both sexes (male and females) and an adult male are free-living; whereas the mature or an adult female of learned have the capability of parasitism. Lernaea cyprinacea attacked massively with the highest mortality and pathogenicity, mostly in the season of summer. The parasite caused ulceration and hemorrhages along with penetration (Carnevia et al., 2003).
The native as well as introduced species of fish fauna in the South American continent are parasitized by 3 species of Lernea, (Boxshall et al., 1997).
The parasite was recorded in the fish fauna of Argentina, Brazil, Colombia, Chile, and Uruguay (Habit et al., 2015).
The harmful effects of the concerned parasite were observed both in wild and cultured fish populations (Yanong et al., 2002).
The species causes serious economic loss in various countries of the world (Rogers, 1979). Lernaeosis is a major disease that is caused by the parasite in the hosts (Hua et al., 2019).
The parasites may cause huge destruction and dangerous diseases in fish fauna, may lead to the extinction of species, and can damage the health of humans by consuming them as food (Habib et al., 2019).
Economic losses have been observed in various formed fishes due to lernaeid ectoparasites globally (Kir et al., 2007).
Lernaeid copepods are considered one of the harmful parasites of freshwater ecosystems; a few individuals can kill young fish (Kabata et al., 1987).