Unit 11

Health Management in Aquatic Species

There are a variety of different areas of emphasis in fish production.  We will begin by considering several of these and their general management features.

Food Fish Production

• Warm water fish-Catfish (75-85oF), Tilapia (80-90oF)   esp. in the Mississippi Delta
• Cold water fish-Salmon and Trout (32-77oF)
• Cool water fish-Hybrid striped bass, Walleye

Bait Fish Production

• Fathead minnows
• Crayfish

Sport fish

• Fish grown for fee lakes and releasing into streams for sport fisherman and for hobby ponds.

Ornamentals

• Tropical fish for aquariums.
• Large tropical fish farm industry in Florida.

In additon to the variety of specialty areas in fish production, a number of different systems are used in fish production.  These include:

• Ponds
• Raceways - an enclosure where water moves in at a rapid rate to carry out waste at the other end. Used commonly in cool and cold water crops. there is a constant water turnover in this system.
• Cages - used in ponds, lakes, rivers and oceans. Used when production outside of a cage is difficult due to the size of the water facility and predators.
• Recirculating system - tanks are used in this system. The water is pumped out, filtered and recirculated. Baitfish and ornamental fish are raised in this type of system.

Rearing methods

• Extensive – low population density, minimal intervention by the farmer and minimal control over the system.
• Intensive – high stocking rate, extensive intervention by the farmer and control over the system.

Producers can raise one species of fish or two or more species together; they can also double crop – for example - Tilapia in the warm season and Rainbow trout in the cold season.  With the variety of ways to raise fish and the variations in environment, it is easy to see how easily fish can become stressed.

  WHAT IS STRESS AND WHY IS IT SO IMPORTANT TO FISH?

Stress: The state caused by a procedure, environmental or other factor which interferes with the fish's ability to grow to market size at the expected rate.

Stressors: Any "challenging factor" which subjects the fish to stress.

Examples of stressors:
(Categories)

1. Poor Water Quality
2. Poor Environmental Conditions
3. Individual Factors
4. Pathogens
5. External forces (mechanical, electrical, human)

Factors influencing fish health

Water quality

1. Temperature – keep in mind the temperatures the different species tolerate. A constant temperature is important.  Sudden temperature changes can kill fish.  If the temperature is below the range for a particular species, the metabolism will slowdown and the fish will not eat.
2. Light – sunburn problems in catfish
3. Oxygen – it is highest in the evening. Fish use oxygen in the evening without replenishment by photosynthesis therefore there is low dissolved oxygen (DO) in the morning.
4. Ammonia – excreted by fish by diffusion. Waste product that goes through the nitrification cycle. Bacteria convert ammonia to nitrite which is then converted to nitrate. Ammonia and nitrite are both toxic to fish

Environment

1. predators – migratory birds
2. pollution – thermal, metal, sewage, particulate, oil, acid rain
3. stocking density – high stocking density can lead to elevated ammonia and nitrite levels and increased incidence of disease.   Streptococcus septicemia is seen in Tilapia at high stocking densities.

  WHAT ARE THE EFFECTS OF STRESS ON FISH?

Stress measurements can be divided into primary (1⁰), secondary (2⁰) and tertiary (3⁰) effects.

PRIMARY EFFECTS

1. Increased plasma levels of corticosteroids
2. Adrenergic response -- increased plasma levels of catecholamines (epinephrine and norepinephrine)

  SECONDARY EFFECTS

1. Abnormal ( or ) blood glucose
2. Abnormal ( or ) plasma free fatty acid
3. Circulating lymphocytes (lymphopenia)
4.   Immunologic function (immunosuppression)
5. Heart/gill blood flow rate

As a general rule, the metabolic effects (secondary effects) of the primary stress mediators remain longer than do the actual elevated mediator levels (days vs. hours). In other words, the stress may be of relatively short duration, but the abnormal levels of substances in the body will remain for longer periods.

  TERTIARY EFFECTS

1. Abnormal behavior (hiding)
2. Abnormal feed consumption
3. Feed conversion efficiency
4. Growth rate
5. Disease incidence
6. Mortality rates

In order for the aquaculturist to successfully raise disease-free fish, he/she must do everything possible to minimize stress.

  COMMON SENSE RULES TO MINIMIZE STRESS IN FISH

1. Maintain excellent water quality, flow and temperature
2. Maintain excellent nutrition
3. Select the best stock
4. Maintain same environment (light, noise, personnel)
5. Minimize handling, transportation, predation
6. Minimize pathogen exposure with biosecurity NOT ANTIBIOTICS
7. Isolation procedures for new stock
8. Therapeutics -- salt
9. Maintain satisfactory stocking density
10. Avoid disease and remove all diseased fish

  BIOSECURITY

Biosecurity involves the exclusion of potential pathogens from an animal production facility.

Examples of biosecurity include:

1. Screens to prevent entrance of wild fish/birds
2. Sanitation/Disinfection of all materials used to handle or house fish, i.e., buckets, nets, tanks, boots, etc.

  EXAMPLES OF DISINFECTANTS USED FOR AQUACULTURE

1. Copper sulfate -- inorganic compound that is a bactericide and a parasiticide.  Be careful when using because this can kill fish if used improperly and will kill all invertebrates.  Important to know the alkalinity of the water before using.
2. Quatenary ammonium compounds -- used as a bactericide.
3. Formalin -- used as a parasiticide and fungicide.

  READ AND FOLLOW ALL LABEL DIRECTIONS WHEN USING DISINFECTANTS

EXAMPLES OF INFECTIOUS DISEASES

• Bacteria – Renibacterium salmoninarum – salmonids, bacterial kidney disease; Aeromonas hydrophila – all fish, septicemia
• Virus – Channel catfish virus disease (herpes virus)
• Fungi – Saprolegnia

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