Bacterial Coldwater Disease

Skip Thompson wrote about Bacterial Coldwater Disease in his last version of Trout Aquaculture Newsletter volume 19 number 1. Here is what he has to say about it...

Bacterial Coldwater Disease (BCWD) is usually seen when water temperature is between 60-70 ^oF. One sign of the disease is the erosion of the tail (caudal) fin. Another sign is a discolored area above and slightly in front of the anal fin that becomes an ulcerated lesion that looks like a 'scooped-out' area.

BCWD usually affects trout less than 6" in size but chronic mortality can be seen in fish larger than 6". As the disease progresses, trout can be seen with the entire caudal fin missing with erosion of the peduncle or fleshy part just in front of the fin. Another name for the disease is peduncle disease.

Prevention & Control

BCWD can apparently enter trout eggs and is not sensitive to a standard treatment of 100 ppm iodophor (Wescodyne, Argentyne, etc). Instead eggs should be disinfected with Hydrogen Peroxide at 100 ppm (4.1 mL/gal of water at 35% active ingredient) (28.7 mL/gal of water at 5% active ingredient).

Routine flow-through treatments at 1.0-1.5 ppm Hyamine^® or other quaternary ammonium compounds reportedly are effective in prevention and in the early stages of infection. However, this approach is not effective once the disease has progressed to erosion of the peduncle and caudal fin.

Stress associated with rearing density contributes to higher level of mortality. In fact, the level of mortality usually will decrease if the trout are simply split into two or more raceways, lowering the density. Mortalities and trout showing the symptoms should be removed quickly since dead trout shed almost 70 times more bacterial than live trout.

If you choose to use an antibiotic, Terramycin^® (oxytetracycline) is not effective when used at the approved rate of 2.5-3.75 g/100 lbs of fish for 10 days. However, Terramycin^® is reportedly effective when used at 16.5 g/100 lbs of trout for 10 days.

Aquaflor^® was approved for use in March 2007 against BCWD at 0.454 g/ 100 lbs of trout for 10 days, and the withdraw period is 15 days. It is worked well in North Carolina. In most instances with BCWD, it is best to first reduce the fish density and then use the antibiotic.