Comprehensive Study Notes on Bacterial Diseases in Fishes Diseases

General Overview of Bacterial Pathogens in Aquaculture

• Bacterial diseases serve as a primary cause of significant economic and biological damage within the fish farming industry.

• Fundamental characteristics of bacteria:

  • They are single-celled, minute organisms.

  • They are ubiquitous in nature, being found in virtually every environment.

• Locations of pathogenic bacteria in relation to fish hosts:

  • The surrounding water column.

  • The external surface of the fish.

  • Internal environments, specifically the intestine or various internal organs.

Ulcer Disease: Characteristics and Etiology

• Disease Classification: Ulcer disease is categorized as either an acute or chronic condition affecting fish populations.

• Etiological Agent: The primary causative bacterium is identified as Haemophilus piscium.

• Clinical Signs and Pathological Development:

  • The disease presents as open sores on the body surface of susceptible fish species.

  • Lesions initially manifest as small papillae.

  • Progression occurs when the top of the papilla erodes, resulting in an open ulcer.

  • The morphology of these open ulcers typically includes whitened skin around the outer periphery with a darkened center.

  • Alternatively, the ulcer may present as a dark center surrounded by a distinct white periphery.

  • Observation in fish pathology shows a reversal of scales and the formation of multifocal ulcers across the body.

Therapy and Management for Ulcer Disease

• Oral Medicinal Treatment:

  • Therapy involves the administration of Chloramphenicol or Oxytetracycline through feed.

  • The dosage rate is set at $35-75\,mg/kg$ of fish body weight per day.

  • The prescribed duration for this oral treatment is $10-15$ days.

• External Chemical Treatment:

  • Dip treatment is utilized for infected individuals.

  • The solution consists of $1:2000\,CuSO_4$ (Copper Sulfate).

  • The immersion duration is $1$ minute.

  • Treatments should be repeated for $3-4$ days.

• Carrier Management:

  • Adult fish frequently act as asymptomatic carriers of the disease.

  • Strict protocols involve examining adult fish for the presence of the bacterium.

  • Infected carriers must be either treated or destroyed to prevent further transmission.

Dropsy: Pathology and Systemic Impact

• Nature of Disease: Dropsy is a highly contagious condition that causes heavy mortality rates, particularly among carp species.

• Etiological Agent and Complex Infection:

  • The bacterium Pseudomonas punctata was traditionally identified as the agent.

  • Current findings indicate that dropsy is primarily initiated by a viral infection.

  • The condition is typically complicated by a secondary bacterial infection.

• Clinical Signs and Internal Pathology:

  • A primary sign is the swelling of the belly (distended abdomen) due to the accumulation of liquid.

  • The accumulated liquid in the body cavity is typically yellow or pink in color.

  • Exophthalmia (bulging of the eyes) is commonly observed.

  • Internally, the intestine shows signs of high inflammation.

  • The liver is noted to be severely affected by the progression of the disease.

Preventive and Curative Measures for Dropsy

• Preventive Measures:

  • Stressors that weaken fish health must be strictly avoided.

  • Keywords for prevention include maintaining optimal water quality, avoiding long-term storage or overcrowding, minimizing unnecessary handling, and ensuring a supply of natural food.

  • Sanitary protocol requires the careful removal and subsequent destruction of all dead fish.

• Curative Procedures:

  • Affected fish should be dipped in a $5\,ppm$ solution of $KMnO_4$ (Potassium Permanganate) for a duration of $2$ minutes.

  • Antibiotics are recommended if there is an imminent danger of widespread infection.

  • A prolonged bath treatment using Chloramphenicol is effective.

  • The bath parameters are $60\,mg \text{ chloramphenicol/litre}$ of water for a duration of $10$ hours.

Fin Rot and Tail Rot: Putrefaction and Treatment

• Etiology: This condition is the result of bacterial infection leading to the putrefaction of the fins.

• Target Areas: The disease specifically targets the caudal fin (tail) or other fins on the fish body.

• Etiological Agent: The causative organism is identified as Flexibacter columnaris.

• Disease Progression Signs:

  • Early stages are marked by a more or less distinct white line appearing at the margin of the fin.

  • This line gradually migrates from the margin toward the base of the fin.

  • The fin tissue becomes torn as the disease advances.

  • Ultimately, the entire fin structure is completely destroyed.

• Treatment Protocols:

  • A dip treatment in a $500\,ppm\,CuSO_4$ solution for $1$ minute is recommended.

  • Bath treatments in dilute solutions of Acriflavine have also been proven highly effective.

Eye Disease in Large and Medium Fish

• Nature of Infection: This is a contagious disease that primarily targets medium and large-sized fish.

• Etiological Agent: Aeromonas liquefaciens is the primary causative bacterium.

• Clinical Signs:

  • Physical impact is localized to the eye, its related nerves, and the brain.

  • Behaviorally, the fish exhibit lethargic actions and decreased activity.

• Treatment and Environmental Control:

  • The primary action is to maintain clean pond water.

  • $KMnO_4$ should be maintained in the pond at a concentration of $1\,ppm$.

  • During initial stages, a medicinal dip is used consisting of $8-10\,mg \text{ Chloramphenicol/litre}$ of water.

  • The immersion duration for this dip is $1$ hour, repeated for $2-3$ days.