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Experience with AQUAFLOR® in North Carolina Trout


Summary: Coldwater disease has been a growing problem in North Carolina trout, resulting in mortality, size variation and slower growth.Trout on 12 North Carolina farms were treated for coldwater disease with AQUAFLOR® (florfenicol), an in-feed antibiotic. After one AQUAFLOR treatment, mortality declined to acceptable levels and coldwater disease did not recur in treated raceways.

By Skip Thompson
NC Cooperative Extension
NC State University


Coldwater disease has been a growing problem in North Carolina trout over the past 3 or 4 years and tends to be seen in trout less than 5 to 6 inches. In the past, mortality escalated rapidly and producers lost anywhere from 5% to 20% of fish and, in some cases, 50% to 60%.

Caused by the pathogen Flavobacterium psychrophilum, the disease had also led to considerable size variation, slower growth and longer times to market by 1 or 2 months, despite treatments with oxytetracycline.

AQUAFLOR® (florfenicol), the first new in-feed antibiotic licensed for aquaculture in more than two decades, was approved in March 2007 for controlling mortality in freshwater-reared salmonids with coldwater disease. This paper summarizes the experience with AQUAFLOR on 12 North Carolina farms. In total, 28 treatments were administered.


As in previous studies1, mortality in fish treated with AQUAFLOR declined to acceptable levels within 4 to 5 days of initiating the 10-day treatment (Figures 1 and 2).

In the N.C. experience2, fish treated with AQUAFLOR did not have a recurrence of coldwater disease.

AQUAFLOR potentially saved up to 600,000 to 700,000 trout in North Carolina in 2007 with an estimated value of $245,000 (~15% of total NC production). On one medium-sized trout farm, losses due to coldwater disease after the use of AQUAFLOR were only a few hundred fish — down from 70,000 fingerlings (28% of the producer’s production) the previous year, before AQUAFLOR was available2.


Even though mortality is often observed to decline within just a few days after initiating AQUAFLOR treatment, AQUAFLOR must be used for 10 consecutive days to provide full therapeutic benefit.

Trials have shown that fish consume feed medicated with AQUAFLOR at the same rate as unmedicated feed1.
Trials have also shown that fish continue
to gain weight throughout the treatment period1.


Clinical disease from ESC is costly due to mortality and reduced weight gain.

Antibiotics can prevent losses during initial ESC outbreaks while at the same time allowing the fish to develop protective immunity.

Protective immunity, however, regardless of the fish’s history, can be overwhelmed due to immunosuppression or a high pathogen load in the pond, resulting in re-breaks. In these cases, proper antibiotic treatment can again minimize losses.

1 Target Animal Safety (TAS) Study on Florfenicol Administered in Feed to Rainbow Trout (Oncorhynchus mykiss Walbaum). (Study No. X00-241-01).

2 Thompson, Skip. Efficacy of AQUAFLOR in North Carolina. United States Trout Farmers Association Mid-Year Meeting, Sept. 2007, Twin Falls, Idaho.

For more information on AQUAFLOR, contact your fish health specialist, veterinarian, diagnostician, extension representative, feed mill or Merck Animal Health.

© 2014 Intervet Inc., a subsidiary of Merck & Co., Inc. All rights reserved.

CAUTION: Federal law restricts medicated feed containing this veterinary feed directive (VFD) drug to use by or on the order of a licensed veterinarian.



For the protection of catfilsh against enteric septicemia
Studies show Aquaflor has no negative impact on mortality, behavior or feed consumption - even when fed at 10 times the recommended dose rate.
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