Fish Health Management Overview

Fish Health Management

• Fish health management is a practice in aquaculture designed to prevent fish disease.
• Treating sick fish is often difficult and expensive.
• Prevention is key; successful management starts with preventing diseases, not treating them.
• Prevention is achieved by maintaining good water quality, proper nutrition, and sanitation.

Significance of Fish Disease

• Fish disease causes substantial monetary loss to aquaculturists.
• Production costs increase due to lost investment in dead fish, treatment costs, and reduced growth during recovery.
• Other factors must be present for active disease to develop in a population.
• Stress-reducing management practices are crucial disease prevention

Relationship of Environment, Fish, and Pathogens

• Disease outbreaks occur when pathogens and unfavorable environmental conditions exist and the fish's defense mechanisms are compromised.
• Balanced environmental conditions lead to good fish health and growth.
• Marginal environmental changes contribute to chronic diseases and reduced growth.
• Severe environmental conditions result in poor growth and overt disease symptoms.

Factors Affecting Fish Health

• Breeding cycles
• Feed management
• High density
• Pollution
• Temperature changes
• Handling
• Transport
• Water quality

Healthy Fish Symptoms

• Body shape and head size are similar
• Body and scales have a bright color
• Gills are red without spots or sores.
• No wounds
• Eats in a timely manner
• Does not approach the edge of the pond

Signs of Fish Disease

• Necrotic fins and tail
• Loss of color
• Wounds on the body
• Enlarged eyes and exophthalmia
• Breathing with mouths
• Distended abdomen and colon filled with fluid
• Heavy mucous on body and gills
• Fish stays near the surface or edges
• Fish does not eat or swims slowly
• Changes in body shape or color

Types of Fish Diseases

• Fungal
• Bacterial
• Parasitic
• Nutritional deficiencies
• Environmental problems
• Protozoan parasites
• Helminth parasites
• Crustacean parasites

Introduction to Aquaculture

• Aquaculture is the farming of aquatic organisms (fish, crustaceans, mollusks, and plants).
• The goal is to meet the rising demand for food fish as the human population grows.
• Aquaculture has seen significant growth, especially in Asia, due to increased yields from farms.

Phases of Aquaculture

• Hatchery Phase: Raises young organisms in controlled environments to ensure high survival rates.
• Nursery Phase: Young organisms are further nurtured before moving to larger systems (ponds, tanks, floating cages).
• Grow-out Phase: Final phase where organisms reach market size and are harvested (desired weight or maturity).

Aquaculture Production Systems

• Extensive System: Low stocking density, low input costs, reliant on natural resources.
• Semi-Intensive System: Moderate stocking density, requires some supplemental feeding and input.
• Intensive System: High stocking density, high resource input (e.g., feed, oxygen), higher disease and environmental stress risk, maximizes yields.

Disease in Aquaculture

• Disease is an abnormality in structure or function of aquatic organisms, displayed through symptoms (e.g., lethargy, visible lesions, erratic swimming, reduced feeding).
• Causes of Disease: Infectious agents (viruses, bacteria, fungi, parasites), poor management practices (overcrowding, inadequate water quality, poor feeding), and environmental factors (poor water quality, temperature fluctuations, pollution).
• Indicators of disease: tissue or organ damage, slower growth rates, reduced size, and increased mortality.
• Consequences of Disease: production losses, decreased product quality, potential rejection, collapse of aquaculture facilities, and threat to industry sustainability.

Disease Management

• Preventative approaches: proper stocking densities, high water quality, balanced diets, biosecurity measures, and quarantine.
• Therapeutic interventions: vaccines and antibiotics (strict regulations). Novel treatments (probiotics, immune boosters). Integrative multi-trophic aquaculture (IMTA) and recirculating aquaculture systems (RAS) for waste reduction.

Disease Development

• Disease development involves three factors: host (farmed fish), pathogens (disease-causing organisms), and environment (surrounding conditions).

Hosts

• Host resilience or susceptibility depends on factors like age and size (smaller are more vulnerable), species (some have natural resistance), defense mechanisms (innate and adaptive immune responses), and health and nutritional state (healthy, well-nourished fish are more resistant).

Pathogens

• Pathogens can be physical (extreme temperatures, UV radiation), chemical (contaminants, toxins, drugs), or biological (viruses, bacteria, fungi, parasites).
• Environmental factors (temperature, dissolved gases, pH, food availability) influence pathogen presence and numbers.
• Infectious agents are characterized by direct transmission and multiplication in host tissue.

Transmission Modes

• Vertical transmission: transfer of pathogens from parents to offspring (eggs/sperm).
• Horizontal transmission: pathogens spread through water, feed, or carrier animals.

Environment

• Essential components of fish culture environments include water, holding systems (tanks, ponds, cages, pens), and stability of physico-chemical parameters (e.g., water quality, temperature, pH, salinity).
• Fish culture activities, and natural fluctuations can affect environmental stability.

Key Water Parameters

• Temperature, pH, salinity, and dissolved oxygen affect fish health. Deviations from optimal ranges can cause stress and disease.

Fish Culture

• Successful fish culture requires understanding and managing the fish's environment.
• Recognizing how environmental factors impact disease aids in effective prevention and control.

Role of Humans

• Successful aquaculture depends on knowledgeable and skilled personnel (technicians, staff).
• Personnel need a deep understanding of the species being cultured.
• Inadequate experience or staffing can lead to costly mistakes and reduced production efficiencies.

Disease Diagnosis:

• A comprehensive history and observations are critical before conducting post-mortem exams.
• Comprehensive diagnoses include parasitological exams, bacteriology, histopathology, and on-site investigations (examining fish, taking samples, evaluating environmental conditions).
• Specialist labs are needed for final diagnostics.

Surveillance and Monitoring

• Regularly monitoring fish (populations, feed, environmental inputs) allows for quick detection of deviations.
• Maintaining records aids in identifying problems, learning from past mistakes, and minimizing costs.
• Frequent monitoring procedures include periodic microscopic evaluation of gills; daily microscopic exam of larvae; and consistent water quality analysis.

Acute Environmental vs Infectious Issues:

• Sudden fish deaths usually point to environmental problems (oxygen depletion, toxic chemicals, temperature extremes).
• Losses that start with a few sick fish often indicate infectious diseases.
• The type of loss pattern over time (e.g. gradual or sudden) can help distinguish between the two.

Stress in Disease Development

• Common stressors include handling, overcrowding, malnutrition, and poor environmental conditions.
• Stress is the sum of physiological responses fish use to maintain or regain normal balance.
• Stress response can impact growth, reproductive capacity, and immunity.
• Prolonged stress can lead to the death of the fish.

Environmental Changes

• Abrupt changes in environmental parameters (e.g., salinity, pH, temperature) stress fish.
• Increased stress makes fish more susceptible to secondary infections.
• Stress compromises fish's defense mechanisms.