Treatment of Bacterial Gill Rot in Common Carp and Crucian Carp

2026-06-05

I. Case Details
Cultured species: Common carp intercropped with crucian carp and silver/white carp.
Cultivation area: 80 mu, water depth 1.3 meters.
Water parameters: Ammonia nitrogen 0, Nitrite 0, pH 8.6
Case description: Five days ago, the daily mortality of carp and crucian carp at the leeward end of the pond was approximately 80 fish. Near the pond’s inlet, some fish exhibited sluggish swimming and reduced responsiveness, while carp showed a gradual decline in feed intake. Water quality parameters were within normal ranges. Post‑mortem examination revealed hepatomegaly and cholelithiasis; no hemorrhagic lesions were observed in the internal organs, nor were there punctate or diffuse hemorrhages in the swim bladder. Microscopic examination did not detect parasites, but the distal ends of the gill filaments were found to be necrotic and congested. The diagnosis is bacterial gill rot.

 

 

II. Treatment Plan
External application: On the first day, disinfect the water by adding 1 liter of Zhongren Gold Iodine (8 mu per bottle) plus 5-Huang Detoxifying Solution (3 mu per bottle).
Day 3: Zhongren Gold Iodine, 1 liter (8 mu per bottle), for water disinfection.

Oral administration: Florfenicol (calculated based on fish body weight) + Doxycycline hydrochloride (calculated based on fish body weight), Wuhuang Detoxifying Liquid, Gandan Kangtai, and aquaculture‑specific multivitamins. Mix one packet of each with a bag of feed and administer continuously for five days.

 

III. Feedback on Results
After two rounds of disinfection, the mortality of carp and crucian carp began to decline; by the fourth day, gill rot had been largely brought under control, and the carp resumed feeding normally.

 

IV. Case Analysis
As water temperatures rise, fry become susceptible to diseases caused by parasites such as gyrodactylids and trichodinids. These parasites primarily attach to the gills; after treatment with antiparasitic agents, the gills may already be damaged. If disinfection is not promptly applied, bacterial gill rot can easily develop. In early spring, when algal populations are low, disinfectants not only eliminate pathogenic bacteria but may also harm some aged algae, potentially reducing dissolved oxygen levels in the pond. For bacterial diseases affecting the gills, iodine‑based products are preferable, as they cause minimal irritation and promote wound healing. Zhongren Golden Iodine is our company’s flagship product—a high‑concentration, sedimentary iodine formulation that enables three‑dimensional disinfection of fish ponds. Its unique formula offers enhanced penetration and superior bactericidal efficacy.

 

Article contributors: Ren Bao, Yang Guang
Editorial Review: Zhang Chuanbao, Lü Zhaoqing, Zang Xueyun

Key words:

Return to List

Previous:

None

Next:

Parasitic Disease Prevention and Control Plan for Protozoa (Sporozoans)