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

2026-06-05

Date: August 15, 2024

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 on August 10, deaths of silver and bighead carps began to occur; by August 15, the daily mortality had risen to over one hundred fish, predominantly bighead carp. The deceased fish uniformly exhibited prominent hemorrhagic lesions on the opercula, 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 a viscous mucus; and the anus was markedly distended and reddened. Water quality in the pond remained generally normal, and carp behavior was unaffected. A preliminary diagnosis is bacterial hemorrhagic disease of silver and bighead carp.

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 Golden Dew to condition the water, helping to prevent recurrence of hemorrhagic disease.

Oral administration: Enrofloxacin plus Gantai Liver‑Bile Formula, plus a hemostatic agent and Wuhuang Detoxifying Liquid, 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 two weeks.

Case Analysis

Starting in August, sustained high-temperature weather sets in. Silver and bighead carps are pelagic fish that habitually reside in the upper water layers; coupled with significant diurnal temperature fluctuations at the surface, they are prone to colds and heatstroke, leading to weakened health. Moreover, high stocking densities further exacerbate the situation, triggering outbreaks 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 molecules, then aggregate at the cell wall, disrupting it and thereby inhibiting bacterial growth and causing cell lysis and death. Benzalkonium bromide can also alter membrane permeability, triggering cytolysis and resulting 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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