Quaglio - Fungal Diseases Flashcards
What are the common fungal diseases affecting fish?
Saprolegniasis (Saprolegnia spp.), Epizootic Ulcerative Syndrome (EUS) caused by Aphanomyces invadans
What is Saprolegniasis, and what causes it?
A fungal disease caused by Saprolegnia spp., a water mold. Common in freshwater fish. Often a secondary infection following physical trauma or poor water quality.
What are the clinical signs of Saprolegniasis?
White, cotton-like growths on skin, gills, or fins; lesions that may lead to secondary bacterial infections; lethargy and loss of appetite in infected fish.
How does poor water quality contribute to Saprolegniasis?
Stress from high ammonia, low oxygen, or poor hygiene compromises immunity, increasing susceptibility to fungal infections.
What are the predisposing factors for Saprolegniasis?
- Physical injuries (e.g., handling, netting)
- Immune suppression due to stress or poor nutrition
- Cold water temperatures favor fungal growth
How is Saprolegniasis treated in aquaculture?
- Salt baths or potassium permanganate treatments
- Improving water quality and minimizing handling stress
- Application of antifungal agents like formalin or malachite green
What is Epizootic Ulcerative Syndrome (EUS), and its causative agent?
A severe fungal disease caused by Aphanomyces invadans. Affects freshwater and estuarine fish. Associated with ulcerative lesions and high mortality.
What are the symptoms of EUS?
- Deep, red ulcerative lesions on the body and fins
- Necrosis of underlying muscle tissue
- Secondary bacterial infections leading to systemic septicemia
What environmental factors favor EUS outbreaks?
- Poor water quality with high organic matter
- Stagnant or polluted water bodies
- Seasonal changes, especially during monsoon periods
How is EUS transmitted?
Spores of Aphanomyces invadans released into water. Infection occurs through open wounds or abrasions.
How is EUS diagnosed?
- Clinical signs of deep ulcers and necrotic tissue
- Microscopic identification of fungal hyphae in lesions
- Histopathology showing mycotic granulomas
What are mycotic granulomas, and their significance in fungal infections?
Granulomas are inflammatory responses to fungal invasion. Seen in chronic cases, indicating immune system response.
What treatments are effective for EUS?
- Broad-spectrum antifungal treatments (e.g., formalin baths)
- Antibiotics for secondary bacterial infections
- Improving water quality and reducing organic load
What are the prevention strategies for fungal diseases in fish?
- Regular monitoring and maintaining good water quality
- Avoiding overcrowding and minimizing fish injuries
- Prompt removal of dead or infected fish to reduce fungal spread
What are the histological findings in fungal infections?
- Hyphae invading tissues, surrounded by inflammatory cells
- Necrotic lesions and granulomas in chronic cases
What is the impact of fungal diseases on fish populations?
- Causes high mortality, especially in stressed populations
- Reduces fish growth and marketability
- Can lead to significant economic losses in aquaculture
How do fungal infections differ from bacterial infections in fish?
Fungal infections often present as cotton-like growths or deep ulcers. Bacterial infections are typically associated with hemorrhages and systemic signs.
What are the common laboratory methods for diagnosing fungal infections?
- Wet mount preparation of lesions for hyphae
- Staining techniques like PAS or Gomori methenamine silver
- Culturing on Sabouraud dextrose agar
What role does stress play in fungal disease outbreaks?
Stress weakens fish immunity, making them more susceptible. Common stressors include poor water quality, overcrowding, and handling.
How does temperature affect fungal growth?
Lower temperatures favor growth of water molds like Saprolegnia spp. Rapid temperature changes can stress fish, increasing susceptibility.
How do fungal diseases contribute to secondary infections?
Fungal lesions provide entry points for opportunistic bacteria. Secondary infections complicate treatment and increase mortality.
What biosecurity measures help control fungal diseases?
- Quarantine new fish stocks
- Regularly disinfect equipment and tanks
- Avoid using contaminated water sources
What is the lifecycle of Saprolegnia spp.?
Asexual reproduction through zoospores released into water. Zoospores infect damaged tissues or organic debris.
Why are fish eggs particularly susceptible to fungal infections?
Lack of protective mucus layer. High organic matter in spawning areas promotes fungal growth.
How are fungal diseases managed in hatcheries?
- Regular use of antifungal treatments (e.g., formalin or malachite green)
- Maintaining optimal water quality and aeration
- Frequent removal of dead eggs or larvae
What is the role of formalin in fungal disease management?
Acts as an antifungal agent. Effective in treating Saprolegniasis and EUS. Used in baths at prescribed concentrations.
How can fungal infections be prevented during fish transportation?
- Minimize handling and physical injuries
- Use clean, aerated water and avoid overcrowding
- Treat transport water with antifungal agents if needed
How do fungal infections impact wild fish populations?
Can lead to large-scale mortality during environmental stress events. Impacts biodiversity and ecosystem stability.
How does Aphanomyces invadans differ from Saprolegnia spp.?
Aphanomyces invadans causes deep tissue necrosis and granulomas. Saprolegnia spp. primarily causes superficial cotton-like growths.
What is the economic significance of fungal diseases in aquaculture?
- Results in high mortality rates and loss of fish stock
- Increases treatment and management costs
- Reduces overall productivity and profitability
