Module 4

• Phylum Platyhelminthes


  Flatworms; dorsoventrally flattened, acoelomate
• MONOGENEA (Phylum Platyhelminthes)


  • Mostly ectoparasite
  • 1-5 mm long
  • Hermaphrodite
  • With direct life cycle
  • With representatives in freshwater, brackish and marine habitats
  • Mostly fish parasites with high host specificity
• Skin Monogeneans


  • With posterior opisthaptor armed with large hooks or anchors, transverse bars, smaller marginal hooklets, clamps, suckers, and squamodisc
• Skin Monogenean Infestation


  1. Attaches on eyes, fins and body surface of fish

  2. Fish rub body against objects

  3. Flashing swimming behavior

  4. Opaque eyes leading to blindness, high mortality, and secondary bacterial infection

  5. Excessive mucus secretion
• Opisthaptor


  • Organ of attachment
  • Hooks or anchors
  • Hamuli
• Prohaptor


  • Fore part with attaching capacities (adhesive pads); Movement; Feeding; Reproduction
• Skin Monogenean Infestation Family Capsalidae (Benedenia spp.)


  • Body large, dorsoventrally flat, oval-shaped
  • Pair of large, disc-like adhesive organs on anterior end
  • 2 pairs of eye spot
  • Large opisthaptor on posterior end
  • Eggs are tetrahedral, with long spiral filament
  • Oncomiracidium mature in 7 days after hatching
• Treatment and Control (Skin Monogeneans)

  1. Horizontal transmission

  2. Freshwater bath treatment

  3. Hydrogen peroxide bath treatment with strong aeration
• Gill Monogenean Infestation


  1. Increased mucus production on darkened body surface

  2. Frayed fins and pale gills

  3. Abnormal swimming behavior

  4. Hemorrhagic lesions in body surface
• Gill Monogeneans


  • Gill lamellar hyperplasia respiratory disorders
  • Mortality
  • Vibriosis is common
• Gill Monogeneans


  • Dactylogyridae
  • Gyrodactylidae
  • Diplectanidae
  • Microcotylidae
• Dactylogyridae


  • Opisthaptor with 14 marginal hooks, 2 anchors, 1-2 connective bars; With 4 eyespots
  • Squamodisc absent
  • Oviparous
• Dactylogyridae


  • Dactylogyrus spp. - on cyprinids
  • Haliotrema spp. - on lutjanids
• Gyrodactylidae


  • Anterior region divided into 2 lobes
  • Opisthaptor with 16 marginal hooks, 2 anchors, and 2 connective bars
  • Eye spots absent
  • Viviparous
• Gyrodactylidae


  • Gyrodactylus spp.
• Diplectanidae


  • Opisthaptor with 14 marginal hooks
  • Eyespots present
  • Squamodisc present
• Diplectanidae


  • Diplectanum spp.
  • Pseudorhabdosynochus spp.
• Microcotylidae


  • Haptor with numerous clamps that have taxonomic importance
  • Clamps either in long stalks or on body surface at posterior end
  • Mouth is adapted for blood feeding
  • Up to 17-20 mm long
• Microcotylidae


  • Microtyle spp.
  • Heterobothrium spp.
  • Heteraxine spp.
• Microcotylidae are on seabream, puffer fish, yellowtail, mullet in East and West Asia; not found in SEA countries
• Life cycle of Pseudorhabdosynochus lantauensis

  1. Mature fluke on gill lamellae

  2. Egg

  3. Free-swimming oncomiracidium

  4. Migrating post-oncomiracidium
• Treatment and Control (Gill Monogeneans)

  1. Freshwater, 15-60 mins, 3d

  2. 5% salt solution, 5 mins

  3. 100-200 ppm formalin, 30-60 min, 3d

  4. 150-200 ppm H202, 30-60 min with strong aeration

  5. Maintain optimum stocking density
• Digenea (Phylum Platyhelminthes) (Trematoda)

  • Mostly endoparasitic flatworms; With ectoparasitic species
  • Dorso-ventrally flat oval body
  • Oral and ventral sucker
  • Gut present
  • Hermaphrodite
  • Larval metacercarial (encysted) and adult stages in fish
  • Indirect life cycle
• Oral sucker


  • Around anteroventral mouth
• Ventral sucker


  • Acetabulum (for attachment and locomotion)
• 3 host of Digenea life cycle

  • Snail
  • Fish
  • Fish-eating vertebrate (bird)
• Digenea


  • Clinostomum sp. (yellow grub or white grub)
• Life cycle of parasitic digenean in fish

  1. Eggs laid by adult

  2. Free-swimming miracidium

  3. Miracidium invades molluscan intermediate host

  4. Cercariae released from molluscan host (snail)

  5. Cercariae encyst in fish intermediate host (fish)

  6. Encysted metacercariae eaten by final host (bird)

  7. Adult digenean in fish
• Digenean infestation


  • Presence of small, white to yellow or brown to black capsules or cysts on the skin, fins, gills. muscle, heart, stomach, or intestine
  • Distended abdomen
  • Disruption of function of vital organs
  • Retarded growth
  • May cause mild diarrhea to cardiac and visceral complications in humans (definitive host)
• Treatment and control (Digenean)

  Elimination of intermediate host
• Cestoda (Phylum Platyhelminthes)


  • Tapeworms
  • Endoparasitic with at least one intermediate host
  • Body (strobila) ribbon-like, segmented (into proglottid) with a single set of reproductive organ or unsegmented
  • With scolex (anterior attachment organ) armed with hooks or suckers
  • 5-70 mm long
  • Gut absent
  • Adults often white, very elongated, and parasitic on host's intestine
  • Larval stage often encysted in visceral organs or muscles with short, unsegmented strobila
• Cestode infestation


  1. Hemorrhagic enteritis due to destruction of intestinal epithelium

  2. Reduced food intake

  3. Reduced market value if present in muscle

  4. Impair reproduction if gonads are infected

  5. Threat to human health (some freshwater cestodes)
• Treatment and control (Cestode)


  Disinfection using lime to destroy eggs; Filtration; Elimination of intermediate host
• Cestode


  • Botriocephalus, Lytocestus
• Cestode infestation


  • Sluggishness; Emaciation; Cessation of feeding
  • Parasitizes the gut, in the intestine, muscle or other internal organs
• Life cycle of cestode

  1. Eggs in feces

  2. Mature to an embryo and develop in copepods

  3. Develops in fish (procercoid penetrates the intestinal wall)
• Treatment and control (Cestode)

  1. No known treatment for cestodes

  2. Elimination of intermediate hosts (copepods)

  3. Disinfection of culture facilities to destroy cestode eggs
• Nematoda (Phylum Aschelminthes)


  • Roundworms
  • Bilaterally symmetrical
  • With well-developed gut
  • Unsegmented
  • Pseudocoelomate
• Nematode infection


  • Elongated, cylindrical worms
  • 1-2 cm long
  • Body tapers at both ends
  • Mouth at anterior end
  • Cuticle with fin transverse striations
  • With more than one intermediate host
• Treatment and control (Nematode)

  1. Eliminate intermediate host (copepod, oligochaate)

  2. Avoid feeding with infected fish

  3. Disinfection of culture facilities to destroy nematode eggs

  4. Anthelminthics - levamisole