Diagnosis and Treatment Protocol for Hemorrhagic Disease in Grass Carp and Silver Carp

2026-06-05

Date: May 10, 2025

Location: Xintan Salt Farm, Binhai County, Jiangsu Province

Cultured species: Common carp intercropped with silver and bighead carps.

Cultivation area: 180 mu, water depth 1.8 meters

Water quality parameters: Ammonia nitrogen 0, nitrite 0.1 mg/L, pH 8.3

Situation description: Starting in early May, after the pond was filled with water, mortality began to occur among silver and bighead carps, persisting for about a week. Daily deaths exceeded one hundred, predominantly affecting bighead carp. Affected fish exhibited distinct hemorrhagic lesions on the operculum, abdomen, and fin bases. Necropsy revealed that the liver and gallbladder were pale in color, enlarged, and fragile; the intestines contained no food but were filled with mucus, and the anus was distended and reddened. Water quality in the pond remained generally normal, and carp showed typical activity. A preliminary diagnosis is bacterial hemorrhagic disease of silver and bighead carps.

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Handling plan:

External application: On the first day, apply a concentrated glutaraldehyde solution (3 mu per bottle) combined with a benzalkonium bromide solution (2 mu per bottle). On the second day, apply Zhongren Jiniodine (8 mu per bottle) together with Wuhuang Detoxifying Liquid (3 mu per bottle). Once the situation is brought under control, use Bishui Jiedu’an for detoxification and EM Jinlu to condition the water, helping to prevent recurrence of hemorrhagic disease.

Oral administration: Enrofloxacin plus Gantai for liver and gallbladder, plus a hemostatic agent, mixed with wheat bran and fed for one week.

Treatment outcome: Following two rounds of disinfection, the mortality of silver and bighead carps gradually declined. By day four, the hemorrhagic disease was largely brought under control, with mortality kept below ten fish. After detoxification and water conditioning, no recurrence was observed within half a month.

Case Analysis

Starting in May, temperatures began to rise, and the pond experienced repeated water inflows. Coupled with significant diurnal temperature fluctuations in the upper water layer, this triggered an emergency response in silver carp and bighead carp, weakening their condition. Combined with high stocking densities, these factors led to an outbreak of hemorrhagic disease.

Glutaraldehyde solution (20%) and benzalkonium bromide solution (45%) are both high‑concentration products compliant with national standards. The free aldehyde groups of glutaraldehyde react with bacterial proteins, inducing protein denaturation and leading to bacterial death. Benzalkonium bromide is a cationic surfactant; its cations bind to proteins via the surfactant molecule, aggregate at the cell wall, disrupt the cell wall, and thereby inhibit bacterial growth and cause cell lysis and death. Additionally, benzalkonium bromide can alter membrane permeability, induce cytolysis, and ultimately result in bacterial dissolution and death. When used in combination, these two agents reduce the corrosiveness and irritancy of aldehydes while enhancing their bactericidal efficacy, demonstrating excellent therapeutic effects against bacterial hemorrhagic diseases.

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