Module 5

• Arthropoda

  • Segmented body covered by exoskeleton and with jointed appendages
  • Includes insects, arachnids, crustaceans
• There are 2,000 parasitic species in Arthropoda, mostly copepods
• Arthropoda are of commercial significance as they affect host survival or cause unsightly changes in flesh
• Phylum Arthropoda


  • Biramous (two parts) limbs
  • Nauplius larvae
• Size of Arthropoda


  0.1 mm – 3.8 m
• Subphylum Crustacea


  • Mostly free-living aquatic animals
  • With terrestrial (woodlice), sessile (barnacle), parasitic species
• Argulus (Subclass: Branchiura)


  Freshwater louse
• Argulosis


  Causative agent
• Argulosis attaches to the skin, fins, buccal or opercular mucosa with 2 conspicuous black spots
• Argulosis causes attachment area to be hemorrhagic or ulcerated
• Species affected by Argulosis

  • Tilapia
  • Milkfish
  • Mullet
  • Carp
  • Snakehead
  • Catfish
• Effects of Argulosis on host

  • Lesions may become necrotic and ulcerated
  • Secondary bacterial/fungal infection
  • Heavy infestation may result in mortalities
• Treatment and control for Argulosis

  • 5 ppm KMnO4, 3-5 min
  • 1 ppm Dipterex, 3-6 h
• Copepoda (subclass)


  • Wide range of body form
  • Single median eye usually bright red and in the center of transparent head
  • Anchored and sessile
  • Attached firmly or move over host's surface
  • Mostly ectoparasitic
• Copepoda have a wide range of hosts and microhabitats on hosts
• Copepoda are 1-20 mm long
• Most research on fish parasites has been on Copepoda, less is known about marine invertebrates
• Parasitic Copepods


  • Ergasilus
  • Caligus
  • Lernaea
• Ergasilidae (Family)


  • Resemble free-living copepods in segmentation
  • 0.9-1.5 mm long
  • Only fertilized females are parasitic
  • Large, recurved, second antennae (for attachment)
  • Cephalothorax – first leg-bearing segment
  • Last segment – associated with swollen genital segment and gives rise to paired egg sacs
  • Mouthparts on mid-ventral surface of cephalothorax
• Ergasilidae attach on gill filaments, gill arches, on body surface, fins
• Effects of Ergasilid infestation

  • Extensive gill damage, severe hemorrhage, inflammation associated with feeding and attachment of parasite
  • Atrophy of gill tips due to blocked blood vessels in gill filaments
  • Emaciated body; slow, weak swimming, discoloration
  • Gill damage results in loss of gill surface area for respiration; leads to suffocation
  • Mortality
  • Reduced weight
  • Reduced length
  • Reduced fat
  • Increased water content
• Treatment and control for Ergasilid


  • 0.15 ppm Bromex, long bath for 1 week
  • 0.25-0.5 ppm Dipterex (Neguvon, Dylox, Masoten), 24 h
• Lernaea (Family: Lernaeidae)


  • Anchor worms
  • 1.2-1.4 mm long
  • Pests in cyprinid and salmonid culture
  • In commercial aquarium species
• Lernaea cyprinacea is optimum at 26-28°C and common in late summer in temperate climates
• Lernaea cyprinacea is prevalent in still or slowly flowing water
• Hosts of Lernaea cyprinacea

  • Carassius carassius and 45 other cyprinid spp.
  • Eels
  • Catfish
  • Goby
  • Cichlids
  • Snakehead
• Parts of Lernaea


  • Cephalothorax with 4 conical and soft horns (holdfast); simple anterior ventral pair; bifurcate dorsal pair
  • Small head projects between the horns
  • Slim, elongated, cylindrical neck and enlarged trunk carries 4 pairs of legs
  • Short and rounded end abdomen with 3 segments
  • Larval stage on gills
  • Adult females attach on body surface, bases of fins, walls of buccal cavities
  • Lodge in superficial layers of body musculature
• Lernaea Life Cycle


  1. Eggs hatch (nauplius and metanauplius stages)

  2. Molting (5 Copepodid stages - parasites in fish surface)

  3. Cyclopoid adults breed, males die

  4. Cyclopoid female penetrates, becomes parasitic adult female and produces eggs
• Effects of Lernaea infestation

  • Holdfast and part of the trunk are buried in the host
  • Most of the trunk and abdomen project in water
  • Swollen and hemorrhagic skin and muscle
  • Ulceration leading to muscle necrosis
  • In infected small fish, parasite can enter the body cavity and damage vital organs
  • Can hinder feeding and growth
  • Secondary bacterial and fungal infection
  • Mortality
  • Mechanical destruction of epidermis and dermis stimulates inflammation
  • Respiratory distress when gills are infected
  • Physical destruction of tissues leading to mortality
  • Induce pressure necrosis, may secrete histolytic and/or digestive enzymes
• Treatment and control for Lernaea

  • Gross and microscopic examinations
  • Treatment over several weeks to break life cycle at larval stage; embedded females are difficult to eliminate
  • 0.25 ppm trichlorphon (Dipterex, Neguvon, Masoten) can eliminate copepodid but not nauplii or adults
  • 3-5% salt solution for control of larval stage; pond drying and liming
• Caligidae (Family)


  • Sea lice
  • Most notorious pests affecting cultured marine fishes
  • Occur year round
  • Adults with large, rounded, flat cephalotohorax
  • Females are larger than male
  • Caligus – with frontal lunules; 239 sp.
  • Lepeophtheirus – no lunules; 107. sp.
  • In tropical and warm temperate waters, occur year-round
  • In cold temperate waters, restricted to salmonids
• Caligid Infestation


  • Transparent parasite, non-permanently attached to skin, fins, and gills
  • 3.9-5.1 mm (female)
  • 2.85 mm (male)
  • 5 phases and 8-11 stages
  • Free-living naupliar stage
  • Infective copepodid stage
  • Attached chalimus stage
  • Free-living, pre-adult stage
  • Adult stage
• Timing of different Caligid stages is dependent on water temperature
• Effects of Caligid Infestation

  • Skin lesions leading to ulcerations
  • Hemorrhagic areas
  • Secondary bacterial and fungal infections
  • Mortalities
  • Osmoregulatory failure due to extensive skin damage
• Treatment and Control for Caligids

  • Freshwater bath, 24 h
  • 0.25 ppm Neguvon, 12-24 h
  • Fallowing, site selection, cleaner fish
• Lernaeopodidae


  • Highly modified copepods parasitic on marine fishes
  • Problem in farmed salmonids in USA
  • Harmful parasite in sparid fish in Japan
  • On gills, body surface, fins
  • Adult females are attached permanently by a bulla implanted in the host
  • Dwarf, short-lived adult male attach to female
  • Life cycle with 6 stages: copepodid, chalimus, adult
  • Male dies after copulation
  • 1-6 months – duration of life cycle
• Effects of Lernaeopodidae


  • Poor appetite
  • Reduced growth rate
  • Reduced fecundity
  • Deformed operculum
  • Mortality
• Damage from Lernaeopodidae


  • Extensive damage and perforation of body wall into viscera
  • Pressure on gill filaments reducing length of filaments
  • Retarded growth of gill filaments
  • Gill histopathology
  • Attachment causes greater damage than feeding activity of parasite
  • Loss of respiratory surface area
• Treatment and control for Lernaeopodidae

  • Gross examination
  • Manual removal
  • On copepodids, 3-4 d interval: 0.85% calcium chloride, 0.2% copper sulphate, 1.7% magnesium sulphate, 0.2% potassium chlorate, 1.2% sodium chloride
  • 0.2mg/kg BW ivermectin, 2-3x/wk
  • 0.2% emamectin benzoate (Slice), 7 d
• Lernanthropodae


  • On gills of moon fish, sea bass
  • With more than 100 sp. parasitic on gills
  • Larger in size than other parasitic copepods; visible with naked eye
  • Feeds on gill tissues and blood of host fish
  • In heavy infections, can cause severe damage to gill tissues, respiratory impairment, osmoregulatory failure, secondary bacterial infections, mortality