Module 6

• Fungi


  • Heterotrophic, no chlorophyll
  • Usually filamentous, multicellular
  • Some are non-filamentous, unicellular
  • Historically compared to plants
  • Saprophytic
  • Parasitic
  • Reproduce both by asexual and sexual
  • Different kinds of spores
  • Reproductive structure used in classification
• Fungal filaments


  • Hyphae (hypha); Body of fungus
  • Mycelium; Network of hyphae
• Septate hyphae


  Hyphae divided by cross-walls
• Non-septate hyphae


  Hyphae without cross-walls (coenocytic)
• Fungal Pathogens of Aquatic Organisms

  • Straminipilous
  • Deuteromycetes
  • Ascomycetes
• Straminipilous


  Lower fungi; Zoosporic fungi; Oomycetes; Most important fungal pathogens of aquatic animals; Cell wall made up of cellulose; With wide, hyaline, and non-septate hyphae
• Deuteromycetes


  Imperfect fungi; Asexual reproduction; Only by production of spores (conidia); Chitin (cell wall)
• Ascomycetes


  "Sac" fungi, "cup" fungi – cup-shaped fruiting bodies (ascus); Chitin (cell wall); Yeast, mushroom
• Saprolegniasis


  Water mold, skin fungus, cotton wool disease; White to brownish cottony growth on eggs and body surface of fish; Also on gills, eyes; Carps, gourami, snakehead; Lethargic, less responsive to external stimuli, loss of equilibrium, mortality; Necrotic epidermis with inflammatory response
• Oomycete fungi (water molds)

  • Saprolegnia spp.
  • Aphanomyces spp.
  • Achlya spp.
  • Pythium spp.
  • Dichtyuchus spp.
• Microscopic examination of oomycete fungi

  Hyaline and coenocytic mycelia; Numerous sporangia
• Treatment and control of Saprolegniasis

  1. Overcrowding, poor handling, poor water quality

  2. Good water quality and circulation

  3. Avoidance of crowding to minimize injury

  4. Good nutrition

  5. NaCl: 22 g/L for 30 min; 30 g/L for 10 min; 1-3 g/L, indefinite

  6. Formalin, 0.4-0.5 ml/L for 1 h
• Epizootic Ulcerative Syndrome (EUS)


  Seasonal epizootic condition in wild and farmed freshwater and estuarine fish; Complex infectious etiology; Red spots on body surface, head, operculum or caudal peduncle; Large red or grey shallow ulcers, often with brown necrosis; Complete erosion of the posterior part of the body or necrosis of both soft and hard tissues of the cranium exposing the brain; Farmed and wild fish; 76 species of freshwater fish (snakehead, catfish, goby, gourami, etc.) and some estuarine fish (menhaden, mullet, perch); Nile tilapia, common carp, milkfish are resistant
• Primary causative agent of EUS

  Fungus – Aphanomyces invadans (A. piscicida); Optimum temperature 20-30oC; Does not grow in vitro at 37oC
• Other associated causative agents of EUS

  • Rhabdovirus – 65 x 175 nm
  • Bacteria – Aeromonas hydrophila
• Associated environmental factors of EUS

  Low water temperature (18-22oC); After periods of heavy rainfall
• Characteristics of EUS


  Characterized by presence of invasive oomycete infection and necrotizing ulcerative lesions, leading to a granulomatous response; Transmitted by cohabitation with diseased fish or exposure to contaminated waters; Fungal hyphae may reach the cranium, kidney and spinal cord; High morbidity (50%) and high mortality (50%)
• Prevention and control of EUS

  1. Prevent entry of non-endemic infected fish

  2. Eradication of infected stocks

  3. Disinfection of contaminated facilities using lime or salt

  4. Reduce stocking density when prevalence is high
• Aflatoxicosis


  Aspergillus flavus, A. parasiticus, Aspergillus spp. – aflatoxin-producing fungi; Common contaminants of improperly stored or expired feeds; AFB1, AFB2, AFG1, AFG2 – direct contaminants of grains and finished feeds; AFB1 – most ubiquitous, most toxic and most well studied; Salmon, channel catfish, tilapia, guppy, carps; Yellowish body surface opaque eye leading to blindness lesions on body surface, fin rot, pale gills; In shrimps - yellowish, then pink to red discoloration of shrimp's body and appendages; brownish red fecal matter; Weak, swim near pond dikes, soft-shell; Fish show abnormal swimming behavior, loss of appetite leading to poor growth, enlargement and yellowish liver with tumors, tumors may spread to kidney, necrosis of liver, high mortality; In shrimps - loss of appetite, retarded growth, increased susceptibility to systemic bacterial infection and shell disease, necrosis of hepatopancreatic tubules
• Prevention and control of Aflatoxicosis

  1. Use only good quality, recently-manufactured, properly stored feeds

  2. Store feeds properly in well-ventilated and cool rooms for not more than 2 months

  3. Regular testing/analysis for aflatoxins
• Larval Mycosis


  Eggs and larval stages of all Penaeus species, crabs, Macrobrachium spp.; Infected stages whitish, weak; Fungal filaments on infected tissues; Marine Oomycetes - Lagenidium spp., Haliphthoros spp., Sirolpidium spp.; Non-septate, highly branched mycelia; With discharged tubes; With or without terminal vesicles (basis for taxonomic identification); Motile zoospores released in the water and implant to susceptible stages; Infected eggs do not hatch; Fungal hyphae replaces the internal tissues of infected host; Up to 100% mortality in 2-3 d after onset of disease
• Prevention and Control of Larval Mycosis

  1. Reduce stocking density

  2. Siphon out sediments and dead shrimps

  3. Rigid water management and sanitation

  4. Egg disinfection with 20 ppm detergent; Rinse well

  5. 0.1ppm trifluralin (Treflan@), 24h, every 2-3d (hatchery)

  6. 0.2 ppm trifluralin (Treflan@), 24h (hatchery); 5ppm trifluralin (Treflan@), 1h (spawners)

  7. 1-10 ppm formalin