Clinical Symptoms and Preventive Measures for Early‑Stage Bacterial Infections in Grass Carp

2026-06-05

Date: June 14, 2025

Location: Baota Lake, Yangxin County, Hubei Province

Cultured species: Grass carp intercropped with silver carp and bream.

Cultivation area: 15 mu, water depth 2 meters.

Water quality parameters: nitrite 0.02; ammonia nitrogen 0.2; pH 8.6

  1. Problem Description

Starting in early June, prolonged periods of overcast and rainy weather led to a gradual onset of fish mortality among grass carp, which persisted through mid-June. The peak occurred when 30 to 40 grass carp died each day. At the base of the gill covers and fin rays, the affected fish exhibited mild reddening and hemorrhaging, along with gill rot; microscopic examination revealed no parasites. Post-mortem examination of the internal organs showed ascites accompanied by enteritis, with the liver appearing darkened. Meanwhile, at the leeward side of the pond, a layer of cyanobacteria and oily surface films was observed.

  1. Handling Plan

For external application: On the first day, in the afternoon, apply Bishui Jiedu’an 5L (30 mu per bottle) by spraying; on the second day, after the weather clears, between 9 and 10 a.m., apply YuKang No. 1 (2 mu per bottle) plus DiDuJing (2.5 mu per bag).

Oral administration: Florfenicol (based on fish body weight) + Gandankangtai + aquaculture-specific multivitamins; mix into feed and administer orally for 5–7 consecutive days.

After five days of oral administration mixed with feed, we monitored the mortality of fish and observed no disease‑related deaths among fresh grass carp, indicating that the condition has been brought under control. With the return to clear weather and rising temperatures from June to August, the feed‑to‑water ratio should be increased accordingly. In routine management, ensure adequate oral supplementation; we recommend administering Hepatobiliary Kangtai combined with a fish‑specific multivitamin for 5–7 days every two weeks to support liver function and enhance the fish’s immune resilience.

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