Fish Disease and Health Management

Introduction:

Aquaculture in Bangladesh is growing rapidly with respect to both quantity and variety of species. Bangladesh ranked 5th position in leading aquaculture producing countries in the world just after China, India, Vietnam and Indonesia (FAO, 2013). Bangladesh produced 30,61,687 mt fish in 2011 of which 15,23,759 mt i.e. 49.76% was produced by the aquaculture sector. Bangladesh contributed 2.43% in world total aquaculture production in 2011. Pond culture represents the mainstay of aquaculture in Bangladesh, accounting for 85.8% of the total recorded production and 57.7% of the area under culture (DOF, 2010).

The current trend in aquaculture development is towards increased intensification and commercialization of aquatic production. Like other farming sectors, the likelihood of major disease problems increases as aquaculture activities intensify and expand. Disease is considered as a primary constraint to the culture of many aquatic species, impeding both economic and social development in many countries. A number of diseases like epizootic ulcerative syndrome, skin erosion, gill damage, tail and fin rot are common in farmed fishes of Bangladesh. In pond aquaculture system, high stocking density and irregularly feed supply is very prone to disease outbreak. Most pond fish farmers do not have a good understanding of health and disease issues in their system. Many diseases of fish are secondary to environmental insult, and can be prevented through proper management. (FAO, 2013).

Types of Fish Disease

Fish ailments can be separated into 4 general types including bacterial infections, fungal infections, parasitic or protozoan infections, and physical ailments and wounds.

Bacterial Diseases: Bacterial diseases are usually characterized by red streaks or spots and/or swelling of the abdomen or eye. These are best treated by antibiotics such as penicillin, amoxicillin, or erythromycin.

Fungal Diseases: Common fungal infections often look like gray or white fluffy patches.

Parasitic Diseases: The most common parasitic disease called "Ich" can be treated most effectively with copper or malachite green in the right dosage. Most treatments will have copper as an ingredient. Many water treatments like "Aquari-Sol" will also contain copper as an ingredient. If the treatment you use is an anti-biotic or copper based, remember to remove all carbon from the filtration system.

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Physical Ailments: Physical Ailments are often the result of the environment. Poor quality water conditions can lead to fish gasping, not eating, jumping out of the tank, and more. Tank mate problems can result in nipped fins and bite wounds.

Table: Types of Fish Disease

Bacterial Parasitic Protozoan Fin Rot Pop-Eye Cloudy Eye External Infections Fish TB Dropsy Septicemia Swim Bladder

Disease Enteric Red Mouth

Argulus Anchor Worm Black Spot -

Black Ick Ergasilus Flukes Nematoda Leeches Uronema

marinum

Velvet or Rust Marine Velvet Brooklynella/Clownfish

Disease Costia Hexamita Ich - White Spot Marine Ich -

Crypt/Marine White Spot

Neon Tetra Disease Glugea and Henneguya Chilodonella

Fungal Fungus Ichthyosporidium

Non-infectious Viral Miscellaneous Tumors Congenital

Abnormalities Injuries Constipation

Herpesvirus disease

Epithelioma papillosum (Fish Pox)

Infectious Hematopoietic Necrosis (IHN)

Viral Hemorrhagic septicemia

Spring Viremia of Carp (SVC) and

Swim Bladder Infection virus (SBI)

Head and Lateral Line Erosion'Hole-in-the-head' Disease

Eye Problems Swim-bladder Disease

Health as a constraint to aquaculture:

The current trend in aquaculture development is towards increased intensification and commercialization of aquatic production. Like other farming sectors, the likelihood of

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major disease problems occurring increases as aquaculture activities intensify and expand. Thus, the aquaculture industry has been overwhelmed with its share of diseases and problems caused by viruses, bacteria, fungi, parasites and other undiagnosed and emerging pathogens. Disease is now a primary constraint to the culture of many aquatic species, impeding both economic and social development in many countries. This situation can be attributed to a variety of multi-faceted and highly interconnected factors such as the increased globalization of trade in live aquatic animals and their products; the intensification of aquaculture through the translocation of brood stock, post larvae, fry and fingerlings; the development and expansion of the ornamental fish trade; the enhancement of marine and coastal areas through stocking aquatic animals raised in hatcheries; the misunderstanding and misuse of specific pathogen free (SPF) stocks (e.g. shrimps); unanticipated negative interactions between cultured and wild fish populations; poor or lack of effective biosecurity measures; slow awareness on emerging diseases; climate change; all other human mediated movements of aquaculture commodities.

However, once a pathogen or disease agent is introduced and becomes established into the natural environment, there is little or no possibility for either treatment or eradication. While consequences of "trickle" infections from wild to cultured populations have predictable consequences due to accessible hosts under cultured conditions, the consequences of culture-borne transmission to wild stocks are harder to predict.

Fish Health management:

This requirement recognizes two related aspects of the fish health management as it applies to aquaculture operations, these being that:

Trans-boundary movement of fry, fingerlings and market size fish should be conducted in ways that minimize risk of spread of fish pathogens; and

Aquaculture farms should adopt effective farm and fish health management practices favoring hygienic measures and vaccines.

Trans-boundary diseases are highly contagious and can spread rapidly across national borders, causing serious socio-economic and public health consequences. The expanding trade in grouper seed for grow-out for the Live Reef Food Fish Trade will, without proper quarantine and health measures, increase risks of pathogen spread. The FAO Technical Guidelines on Aquaculture Development states that transfers of eggs, fingerlings and adults among river basins or large water bodies should be avoided. Introduced species are often preferred because they attract higher prices and have greater export potential.

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Where possible, Governments should assist in ensuring grouper seed and broodstock are sold free of disease by:

Requiring a breeding and disease history be maintained for broodstock and seed that is be transferred within the country or exported. Where possible, only eggs or seed that are certified as specific pathogen free should be used (including those supplied to backyard nurseries);

Requiring the use of approved chemicals and drug use prior to and during transport of seed and marketable fish  and

Developing guidelines on certifying seed for trans-boundary movements.

Most disease outbreaks occur during the first 2 - 12 weeks after initial placement in the grow-out cages. And depends on the condition of the fish on arrival, their size and fish species involved. Regular monitoring of the health of cultured grouper is important for effective prevention of diseases caused by infectious micro-organisms or stress, and early detection of health problems. The main areas for consideration that will facilitate the prevention and containment of diseases include:

Poor handling and transportation techniques that induce stress, lower water quality and cause external injuries;

Disease transmission in transportation through contaminated water; Disease transmission caused by farming multiple species that come from

various locations in close proximity and by regularly exposing newly introduced juveniles to existing pathogens in the cages;

Poor feed handling and storage of trash fish or artificial feeds

The socio-economic impacts of higher costs imposed on small-scale aquaculture nursery operators in adopting disease prevention and treatment programs should be considered in terms of higher benefits. Governments, non-government organizations and regional agencies should facilitate extension, outreach and technical support activities that raise awareness of farmers and aquaculture operations on health management issues including:

Technical training to farm managers and workers on the surveillance, monitoring and early detection of disease in fish and the course of action to be taken once diseased fish are identified; 

The availability of diagnostic services to identify those pathogens already present in the culture environment and the methods for sending specimens for diagnosis; and

Common diseases in grouper species and their prevention and treatment.

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Routine disease prevention or prophylactic treatment should be incorporated into both the transport and packing of grouper seeds the farm management activities for newly arrived seed/fish. The main principles of disease treatment and control are to:

Establish an accurate diagnosis; 

Select the appropriate environmentally responsible treatment; and

Evaluate management practices and identify areas critical to the prevention of future outbreaks.

Any chemicals or drugs used should be acceptable in terms of risk to human health or the environment and to end markets, should be easily available and importantly, their correct use must be understood.

Responsible Practice:

Controlling trans-boundary movements. Trans-boundary movements of fry, fingerlings and market size fish should be conducted in ways that minimize risk of spread of fish pathogens

Utilize existing international codes of practice. Existing international codes of practice that address trans-boundary movement and use of introduced species in aquaculture should be used as a framework to develop codes relevant to tropical latitudes and species. Existing databases should be used to identify and determine risks from imported species. 

Recording breeding and disease history. Breeding history and disease history should be maintained for aquaculture stocks to facilitate exchange of disease free brood stock and seed both within the country and for export.

Farms should ensure fish are sold free from disease. Aquaculture farm should use eggs or seed that are certified as specific pathogen free (including eggs supplied to backyard nurseries) 

Accessing fish health management advice. Governments, non-government organizations and regional agencies should facilitate extension, outreach and technical support activities that raise awareness of farmers and aquaculture operations on health management issues including technical training, diagnostic services and disease prevention and treatment.

Adopting farm and fish health management practices:

Fishers, exporters and farms shall adopt effective fish health management practices for the prevention and containment of diseases by:

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Reducing stress potential for injury during handling and transportation,

Minimizing the potential for disease transmission among different cohorts and species; and

Implementing good handling and storage practices for trash fish and artificial feeds

Aquaculture farms shall adopt effective prophylactic treatment programs for the prevention, treatment and control of disease through:

Establishing effective and accurate diagnosis procedures,

Selecting the treatments that meet acceptable environmental and human health risks; and

Evaluating management practices and identifying critical prevention areas

Recognize socio-economic impacts: The socio-economic impacts of higher costs from adopting disease prevention and treatment programs should be offset against potential higher benefits

Good Farming Health Management Practices:

A health management program has several requirements and must cover all levels of aquaculture activity. At the production level, the requirements for a healthy environment include strong healthy seed and juveniles, proper nutrition, appropriate waste management, optimal water quality, and regular monitoring. At the farm site level, good record keeping is essential. It should cover all aspects of farm operation. Farmers should be trained to understand the importance and value of such information in determining the course or nature of a disease outbreak, providing accurate and rapid diagnosis, and enabling sensible management decisions for intervention and control. Record keeping is crucial to aquaculture and can go a long way in supporting effective health and productivity management efforts.

A good farm profile should contain the following information:

Treatment administered;

Clinical signs (behavior, appearance);

Farm lay-out (inflow, outflow, connection of ponds);

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Animals cultured (species, numbers, origin, age classes);

Yields (per pond, per cage, per farm, normal survival rates);

Nutrition (live food, manufactured food, sources, feeding practices);

Management practices (continuous stocking, closed operation, stocking densities);

Mortality data (affected sites, cages, ponds along with approximate percentages and numbers); and

Unusual events (abnormal weather changes, mortality above average, yield below average, land-use activity, run-off, spills, abnormal growth, spawning events).

In addition to regular record keeping, there should be a continuous monitoring and updating of information (new animals on farm, change of feed, new ponds connected, and new farms upstream).

Economic investments and opportunities in aquatic animal health:

Economic impacts have also been expressed in terms of costs of investment in disease research and control and health management programmes. so far no systematic economic assessment has been carried out. In the foreseeable future, there will be increasing demand for such assessments in order to gain attention and continuous support from both the public and private sectors.

Conclusion:

Aquaculture activities in Bangladesh are predominantly pond based. Addressing health questions with both pro-active and reactive programs has become a primary requirement for sustaining aquaculture production and product trade. The current strategy in the Asia-Pacific region emphasizes responsible health management to minimize the risks of disease incursions brought about by the movement of live aquatic animals and their products. The risk of major disease incursions and newly emerging diseases will keep on threatening the sector, and unless appropriate health management measures are maintained and effectively implemented, the government and private sectors will be faced with more costs in terms of production losses and the efforts needed to contain and eradicate diseases, funds that would have been better spent in preventing their entry into the system. Focusing efforts on prevention, on better management practices and on maintaining healthy fish maybe more important than focusing on why fish get sick. Health management is a shared responsibility, and each stakeholder's contribution is essential to the health management process.

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