Saprolegniasis

Improve oxygenation and water, isolate safely and remove dead eggs with clean tools. Minimise handling and protect skin from abrasion. Do not tear away a deeply attached mass because this can enlarge the wound and does not remove filaments within tissue.

Saprolegniasis is an aquatic oomycete disease, chiefly involving Saprolegnia, that colonises eggs or damaged tissue. Oomycetes are not true fungi despite producing cotton-like growth. Infection is often secondary to trauma, cold stress, poor water quality or another disease, so predisposition must be identified.

White, grey or brownish tufts arise from skin, fins, gills or eggs and may trap debris, becoming darker. Tissue beneath can be eroded or necrotic; affected eggs turn opaque and growth spreads to neighbours. A film on new wood without living-tissue involvement belongs to a different context.

Columnaris and other bacterial infections can form pale plaques but not long hyphae; mucus and necrotic tissue may look fuzzy. Peritrich ciliates show bell cells on stalks. White growth on new wood is often local biofilm and should not be called saprolegniasis without an affected host.

Zoospores and filaments are common in the environment, but intact skin and healthy eggs resist better. Transport, aggression or handling injuries, dead eggs, detritus, adverse temperature and reduced defences create entry points. Environmental presence is not disease until compatible invasion occurs.

Zoospores and filaments are common in the environment, but intact skin and healthy eggs resist better. Transport, aggression or handling injuries, dead eggs, detritus, adverse temperature and reduced defences create entry points. Environmental presence is not disease until compatible invasion occurs.

Examine a fresh mount from the active lesion margin or affected eggs for broad, branching, generally nonseptate filaments. Cytology and histology help demonstrate invasion and coinfection; culture must be interpreted with sampling site. Photograph before cleaning and reconstruct the initiating injury.

Improve oxygenation and water, isolate safely and remove dead eggs with clean tools. Minimise handling and protect skin from abrasion. Do not tear away a deeply attached mass because this can enlarge the wound and does not remove filaments within tissue.

The plan must address both oomycete and predisposing lesion. Options for eggs, dips or fish treatment differ by species, stage and regulation and require veterinary or official-label verification; no doses are provided here. Reassess lesion margin and growth because loss of visible ‘cotton’ alone does not prove healing.

Gill involvement, rapid expansion, deep lesions, anorexia or multiple affected animals require veterinary review. Recurrence after treatment suggests unresolved trauma, water quality or coinfection. Sample before necrosis and secondary colonisers erase the initial picture.

Reduce capture and transport trauma, maintain appropriate temperature and water, and promptly remove nonviable eggs and dead tissue. Disinfect equipment between spawning groups and avoid overcrowding incubators. Investigate aggression or parasites that breach skin.

Gill involvement, rapid expansion, deep lesions, anorexia or multiple affected animals require veterinary review. Recurrence after treatment suggests unresolved trauma, water quality or coinfection. Sample before necrosis and secondary colonisers erase the initial picture.