Cold Water Disease: causes, symptoms and treatment

Cold Water Disease (Flavobacterium psychrophilum) — etiology, symptoms, diagnosis, active-substance medication, recovery and prevention; mortality without treatment: very high.

Overview

Cold-water relative of columnaris causing tail erosion (peduncle) and systemic disease at temperatures below 16 C. Major issue in salmonid hatcheries. Causative agent: Flavobacterium psychrophilum. Transmission: water. Incubation: 3-14 days. Reported mortality without treatment: very high.

Symptoms

necrosis of tail peduncle
fin erosion
darkening
lethargy
spinal deformity in juveniles
high fry mortality

Causes

Outbreaks are typically triggered by chronic stress, poor water quality, temperature swings, overcrowding, or the introduction of unquarantined fish. The pathogen spreads via free-swimming or waterborne stages in shared water.

Diagnosis

Diagnosis is based on clinical signs (lesions, hemorrhages, behaviour) combined with bacterial culture and Gram-staining where available. Differentiate from co-infections with other Gram-negative pathogens; antibiotic sensitivity testing improves treatment success against Flavobacterium psychrophilum.

Treatment

Effective treatment requires isolating affected fish in a quarantine tank, identifying the pathogen, administering the appropriate active substance at the correct dose and duration, and supporting recovery with stable water parameters and nutrition.

Step 1: Quarantine

Set up a bare-bottom quarantine tank with a mature sponge filter, heater, and aeration. Match temperature and pH to the display tank, and acclimate fish slowly. A bare bottom simplifies daily siphoning and prevents medication from being absorbed by substrate.

Step 2: Medication

Florfenicol or oxytetracycline. Florfenicol 10 mg/kg in feed daily for 10 days; oxytetracycline 75 mg/kg as alternative. Vaccines available for trout farms. (duration: 10 days)

Step 3: Recovery

After medication, perform a 30-50% water change and run fresh activated carbon for 24-48 hours to remove residues. Continue feeding a high-quality, varied diet with vitamins and immunostimulants. Reintroduce fish to the display tank only after at least one week without recurrence of symptoms.

Prevention

avoid temperatures below 16 C if possible
vaccinate trout fry
minimize handling stress
good fry husbandry