April 22, 2024
Fish Skin Disease

An In-Depth Look at Fish Skin Disease: Causes, Symptoms, and Control Measures

Major Fish Skin Diseases

Bacterial infections

Bacterial infections are one of the most common causes of fish skin disease. Some of the common bacterial infections include:

Flexibacter columnaris: Commonly known as columnaris disease, it is caused by the bacterium Flexibacter columnaris. It affects both freshwater and marine fish species. Infected fish show grey or brown necrotic lesions on their skin, fins and gills. It spreads rapidly in fish farms causing high mortality.

Streptococcus iniae: It is one of the major bacterial pathogens of freshwater and marine fish species worldwide. Infected fish show skin erosion, patchy scales and reddish skin lesions. Streptococcus iniae poses a significant threat to cultured fish in intensive and semi-intensive systems.

Aeromonas salmonicida: It causes furunculosis or bacterial fish furunculosis disease primarily in salmonids and other cold water fish species. Affected fish develop dark red skin ulcers with swollen tissue around it. Farmed salmon and trout are particularly susceptible to this deadly skin disease.

Viral infections

Viral skin diseases can devastate entire fish populations and fish farms. Some common viral skin diseases include:

Viral Hemorrhagic Septicemia virus (VHSV): It affects both freshwater and marine Fish Skin Disease species. Infected fish show pinpoint hemorrhages on skin, eyes, fins and tissue below the skin. Outbreaks can cause high morbidity and mortality.

Infectious Hematopoietic Necrosis virus (IHNv): Affecting salmonids, it causes skin discoloration, fin rot and hemorrhaging. Young fish are more severely affected. The disease requires extreme control measures to prevent its spread.

Spring Viremia of Carp Virus (SVCV): It is highly contagious and pathogenic for cyprinid fish species especially common carp. Affected fish show darkening of skin, fin erosion and eye hemorrhages. Mass mortality incidents have been reported from intensive carp farms.

Fungal infections

Fungal pathogens frequently take advantage of wounds and tissue damage caused by other diseases and stresses to invade fish skin. Some common fungal skin diseases include:

Saprolegnia: Also known as saprolegniasis or cottonwool disease, it infects fish eggs, fry and fingerlings of various species. Infected fish show fluffy white fungal growth on skin, fins and gills which can spread rapidly in hatcheries and nurseries.

Branchiomyces: It causes branchiomycosis disease in a wide range of marine and estuarine fish species worldwide. Disease is characterized by extensive skin and gill erosion with white fungal growth. Heavy infections lead to severe septicemia and mortality.

Aphanomyces: Responsible for ulcerative skin lesions on fish, it afflicts both freshwater and marine fish populations. Skin ulcers are broad, irregular and invasive in nature compromising fish health.

Parasitic infections

Various parasites also infect fish skin directly or predispose fish to secondary infections. Important ectoparasites infecting fish skin include:

Ichthyophthirius multifiliis: Commonly known as ich or white spot disease Fish Skin Disease , it is a ciliate protozoan parasite that causes white spots on skin and gills of freshwater fish. Heavy infections can destroy gill tissues leading to septicemia and death in untreated fish.

Gnathiid and caligid copepods: As ectoparasites gnathiids and caligids feed on fish mucus, tissues and blood. They cause skin erosion, ulceration and secondary infections, thereby compromising fish health and performances.

Dactylogyrids: Flatworm monogenean parasites like Dactylogyrus readily infect the gills and body surface of various freshwater fish species including carps. Heavy infections damage gill tissues and osmoregulatory functions.


These fish skin diseases are immensely detrimental for sustainable aquaculture and fish farming for multiple reasons:

– They cause significant morbidity and mortality especially under intensive culture conditions. Mass mortalities wipe out entire stocks.

– Survivors become debilitated physiologically and are more prone to handling stress, secondary infections and poor performances.

– Skin damages compromise outer protective barrier increasing susceptibility to other pathogens and environmental stresses.

– Outbreaks lead to huge production losses, distressed sales and abandoned culture efforts in affected zones.

– They spread rapidly where culture hygiene is compromised threatening industry food security and livelihoods.

– Some diseases like VHS, IHN are transboundary in nature impacting international trade and market access.

– Preventive measures and disease control add tremendous costs escalating production overheads for farmers.

Prevention and Control

Timely identification of skin diseases and implementation of effective prevention and control measures are crucial for sustainable aquaculture development:

– Practice of strict biosecurity protocols – Disinfection of water, equipment, structures, preventing interactions between wild and cultured stocks etc.

– Surveillance and screening of broodstock, fry and fingerlings before their introduction to farms.

– Maintaining optimal water quality through adequate rates of water exchange, aeration and maintaining recommended levels of physico-chemical parameters.

– Implementing all-in all-out production cycles for individual rearing units.

– Following recommended vaccine schedules where effective vaccines are available against specific diseases.

– Prompt treatment of any disease outbreaks under expert guidance using approved chemicals and designing effective farm management strategies.

– Husbandry and management practices that avoid fish stress, crowding and injuries predisposing fish to health issues.

– Training aquaculture workers in disease identification, hygiene maintenance and implementing biosecurity protocols diligently.


1. Source: Coherent Market Insights, Public sources, Desk research
2. We have leveraged AI tools to mine information and compile it