Fish health management in aquaculture refers to the set of practices and strategies aimed at preventing diseases among fish. Once fish become ill, it can be challenging to save them.
Effective fish health management starts with disease prevention rather than treatment. Preventing fish diseases involves maintaining optimal water quality, providing proper nutrition, and ensuring good sanitation practices. Without these fundamental aspects in place, it becomes difficult to stop outbreaks of diseases that take advantage of weakened fish. Fish are constantly exposed to potential disease-causing agents like bacteria, fungi, and parasites, even if efforts are made to eliminate them through sterilization methods like ultraviolet treatment and ozonation. Subpar water quality, inadequate nutrition, or weakened immune systems due to stress provide openings for these agents to cause diseases. While medications can be used to treat such diseases, they are not a substitute for proper fish care.
Regularly observing fish behavior and feeding habits allows for early detection of issues, enabling diagnosis before the majority of the fish population becomes sick. If treatment is necessary, it is most effective when administered early in the disease’s progression, while the fish are still in good health.
The impact of fish diseases on aquaculture is significant in terms of financial loss. Disease outbreaks increase production costs due to losses from dead fish, the cost of treatment, and reduced growth during recovery. In natural environments, fish diseases have less noticeable effects because sick fish are swiftly removed by predators, and fish populations are less crowded than in aquaculture settings. However, when fish are densely packed and stressed in captivity, parasites and bacteria that are normally of minor concern in natural settings can lead to substantial problems.
It’s important to understand that fish diseases are typically not solely caused by pathogens infecting host fish; other factors and conditions must also be present for active diseases to develop within a fish population.
If you suspect that your fish may be falling ill, the first step is to assess the quality of the water in which they are kept. If you lack the necessary tools for water quality testing, reach out to your local county extension office. Some counties may have these testing kits available, and your extension agent can offer assistance. In cases where your county does not possess such kits, you can contact the nearest aquaculture extension specialist listed at the end of this publication. For those considering commercial fish production, it’s highly advisable to invest in a water quality test kit and acquire the knowledge to use it effectively. Even an introductory kit for freshwater aquaculture, which comes at a minimal cost, can potentially save you thousands of dollars in fish losses with its first use.
In ponds, low oxygen levels are a common culprit behind fish mortality, particularly during the summer. Disease outbreaks in crowded vats or tanks are often associated with elevated levels of ammonia. Additional fact sheets are available that provide explanations on oxygen and ammonia cycles, along with guidance on managing these water quality issues. Generally, when dealing with a fish disease outbreak, it’s essential to monitor dissolved oxygen, ammonia, nitrite, and pH as part of a basic water quality assessment. Depending on your specific system, parameters such as total alkalinity, total hardness, nitrate (for saltwater systems), and chlorine (if using city water) may also be significant.
It’s advisable to maintain daily records that can be readily accessed in the event of a fish disease outbreak. These records should include information such as the dates when fish were introduced, their initial size, the source of the fish, feeding rates, growth rates, daily mortality figures, and water quality measurements. This data is invaluable for aquaculture specialists working to address your fish health issues. Well-kept records, along with detailed observations of abnormal fish behavior and physical symptoms, as well as the results of water quality tests, provide a comprehensive case history for diagnosticians analyzing your situation.
If you decide to send fish samples to a diagnostic laboratory, it’s crucial to collect live, diseased fish and place them in a freezer bag (without water). These samples should be shipped on ice to the nearest facility. For smaller fish, they can be shipped while alive by placing them in plastic bags partially filled (around 30 percent) with water, and oxygen can be injected into the bag before sealing it. To minimize temperature fluctuations during transit, it’s advisable to use an insulated container when shipping live, bagged fish. In addition to fish samples, including a water sample collected in a clean jar for analysis is also recommended.
Fish diseases can be divided into two main categories: infectious diseases and non-infectious diseases. Infectious diseases result from the presence of pathogenic organisms in the fish’s environment or transmitted by other fish. They are contagious and may require treatment to control outbreaks. On the other hand, non-infectious diseases are caused by factors such as environmental conditions, nutritional deficiencies, or genetic abnormalities. These diseases are not contagious and typically cannot be cured using medications.
Infectious Diseases: Infectious diseases in fish can be further classified into parasitic, bacterial, viral, or fungal diseases.
- Parasitic Diseases: These are commonly caused by microscopic organisms known as protozoa, which inhabit the aquatic environment. Protozoans often infest fish gills and skin, leading to symptoms like irritation, weight loss, and eventual death. Many protozoan infections can be controlled using standard fishery chemicals such as copper sulfate, formalin, or potassium permanganate.
- Bacterial Diseases: Bacterial infections can be internal or external. Internal infections usually require medicated feeds containing approved antibiotics. Fish with bacterial infections may display symptoms such as hemorrhagic spots, ulcers, enlarged abdomens, and protruding eyes. External bacterial infections can cause skin erosion and ulceration. Proper handling can prevent some external bacterial infections, like Columnaris.
- Viral Diseases: These are challenging to diagnose without specialized laboratory tests and cannot be cured with specific medications. A notable viral infection affecting fish production in the southeastern United States is Channel Catfish Virus Disease, caused by a herpes virus. Consultation with a fish health specialist is advisable if you suspect a bacterial or viral disease.
- Fungal Diseases: Fungal spores are common in aquatic environments and usually don’t affect healthy fish. However, when fish are injured, have external parasites, or suffer bacterial infections, fungi can colonize damaged tissue on their skin. Infected areas may appear as cottony growth or brown matted areas. Formalin or potassium permanganate can be effective against most fungal infections.
Non-Infectious Diseases: Non-infectious diseases can be broadly categorized as environmental, nutritional, or genetic.
- Environmental Diseases: These are crucial in commercial aquaculture and result from factors like low dissolved oxygen, high ammonia levels, elevated nitrite levels, or the presence of toxins in the water. Proper water quality management is essential to prevent most environmental diseases.
- Nutritional Diseases: Diagnosing nutritional diseases can be challenging. For example, “broken back disease” in catfish is caused by vitamin C deficiency, leading to spinal deformities. Another catfish nutritional disease is “no blood disease,” possibly linked to a folic acid deficiency. These issues can often be resolved by adjusting the fish’s diet.
- Genetic Abnormalities: These include conformational oddities like tail deformities. While many genetic abnormalities have minimal significance, it’s advisable to introduce unrelated fish into the breeding program periodically to reduce inbreeding.
Summary: Fish diseases can pose challenges for both commercial producers and recreational pond owners. Many disease outbreaks in captive fish populations are associated with stressful conditions such as poor water quality, overcrowding, or inadequate nutrition.