Fish emergency medicine (Proceedings)


Emergency situations are a common scenario for the 'fish' practitioner. As with any other species, immediate action should be taken to stabilize the patient before any attempt is made to correct underlying problems. This lecture will describe the steps for providing first aid to the critical patient.

Objectives of the Presentation

Emergency situations are a common scenario for the 'fish' practitioner. As with any other species, immediate action should be taken to stabilize the patient before any attempt is made to correct underlying problems. This lecture will describe the steps for providing first aid to the critical patient.

Key Points

     • Emergency therapy

     • Further treatments

     • Common scenarios

     • Common drugs

     • Prevention

Overview of the Issue

      First Aid Advice

A common scenario presented to veterinarians is the concerned owner of an aquarium or fish pond calling for advice after a few fish have suddenly died. As with other species, a diagnosis cannot be made over the phone, but initial supportive therapy can be begun to try to prevent more losses. The following steps provide a rough guide for the owners to follow:

           1. Immediately isolate any sick animals, and remove any dead individuals. Parasites and other pathogens will quickly leave the dead host and seek out live hosts spreading the disease throughout the entire population.

           2. Ensure adequate aeration in the system. Some aquatic systems can normally be maintained with minimal aeration; however, diseased fish have an increased need for oxygen, and just as with critically ill terrestrial or avian patients, they should be kept in an enriched oxygen environment. Remember that gas exchange happens at the surface of the water, so it is important to have a large surface area and to keep the surface water moving.

           3. Check the filtration system. Make sure that both the mechanical and chemical properties of the filtration system are working. In pond settings filters sometimes get clogged with a thick layer of mud, allowing the water to bypass the different filtration steps. As a result the water simply trickles back to the system unchanged. In an aquarium setting, make sure that the activated charcoal in the filter is not expired and that the filter floss has been cleaned or changed.

           4. Stop all feeding. The sick fish will not eat, and the leftover food will sink, decompose, and result in increased ammonia levels, creating a more toxic environment.

           5. Change one-third to one-half of the water. Use dechlorinated water, or water treated with water conditioner, to dilute any toxic substances present in the fish's environment. Complete water changes are not recommended, as such drastic changes of the environment could become an additional stress factor and possibly kill the sick fish.

           6. Check water quality immediately. Levels of ammonia, nitrite, nitrate, pH are most important. Even if previous testing has been done, a repeat of the test is still advisable to rule out any errors and to compare the water quality after the partial water change.

           7. If no salt has been added to the system before, add non-iodized salt at 2 g/L. This quantity equals a 0.2% solution. For example a 10 gal system would need about 80 g. of salt!! Initially add 50% of the calculated value of salt, wait 24 hours, and then check the water salinity level. If it is at the appropriate level, add the rest of the calculated value. Kosher table salt is non-iodized, readily available, and cheap. Salt will help to improve the osmotic balance between freshwater fish and their environment and therefore reduce stress on the fish's metabolic system. Salt added at this concentration will not harm the fish in any way. In addition it may also kill many ectoparasites and will block the uptake of toxic ammonia by the gills. The only negative side-effect is that this concentration might possibly kill some freshwater plants. Also before adding salt make sure that the charcoal in the filter does not contain zeolite, as adding salt will release ammonia bound to this filter medium.

Further Investigation

Once the system has been initially stabilized, attempts should be made to prevent ongoing losses. Good communication with the owner is a key to success in diagnosing the underlying problem. It is a good practice to have a standard questionnaire prepared which can be filled out by the owner while first aid is being initiated. In questioning the owner it is extremely important to get a feeling for their understanding of fish medicine. It is a common scenario that multiple antibiotics and antiparasitics have already been applied to the system by the owner, and therefore that the pathogens present might already exhibit multi-drug resistance. Questions such as these establish a minimum database from which to pursue further diagnostics:

     • How long have you been keeping fish?

     • When did you first notice these problems?

     • How long have you owned the sick fish?

     • Are there other fish in the same tank or pond with the sick fish, and if so, how are they now?

     • What is the size (volume) of the tank or pond and how is it heated, filtered, and aerated?

     • What and how often do you feed your fish?

     • Have the fish already been treated? If so, by whom and with what medications?

     • Is there a possibility that the fish were exposed to some type of toxin?

Common Scenarios

Abnormal water chemistry parameters. This is the number one fish killer. Careful monitoring of these parameters through regular water checks and corrective water changes can save the life of many fish

Suffocation. This usually originates from an increase in water temperature which results in a decrease in the oxygen available in the system.

Chlorine intoxication. The use of chlorinated tap water without pretreatment with dechlorinating agents can create lethal chlorine levels which can kill all fish within hours. It is important to note that simply aging tap water will not effectively make it safe to use if chloramine complexes are present since they will not evaporate out of water the way chlorine will and will remain at harmful levels.

Tank mate aggression. Fish are very territorial and aggressive individuals can prevent other fish from eating or even inflict actual wounds. High stress levels in the subordinate fish can increase their susceptibility to disease.

Sepsis. Systemic infections are usually the result of a chronic stressor in the environment which has lowered the effectiveness of the fish's immune response.

Parasitic infestations. Macro or microscopic in size, infestation by ecto- and endoparasites can result in severe losses within a collection of fish. Routine diagnostic exams for fish parasites should always be included in routine examinations in order to avoid increases in parasitic populations.

Emergency Drugs

      Hydrogen peroxide (H2O2)

As water temperature increases, the concentration of dissolved oxygen decreases. If fish show signs of suffocation, through piping behavior, an increase in the dissolved oxygen concentration is needed.

Use commercially available H2O2 (3% solution) at a rate of 24-25 ml per 10 gal of water. Caution: It is a very caustic agent in the concentrated form, and the gills can be damaged by direct contact.

Ice Packs

These are a great way to cool down water temperatures, and thereby increase the oxygen carrying capacity, of the water. Owners of ponds should always have a few ice packs in the freezer just for this purpose.

Sodium bicarbonate (Baking Powder)

When a system crashes the pH often falls significantly. Sodium bicarbonate will act as a buffer and prevent the pH dropping too low. One teaspoon per 10 gal. water should be enough.


This should only be used in the shocky or traumatized patient at a dose of 1-2 mg/kg.


When choosing an appropriate antibiotic to fight infections in fish, keep in mind that most bacterial pathogens of fish are gram-negative.


The best way to deal with emergencies is simply to avoid them. Make sure that you have educated your fish client appropriately right from the initial visit. This education can be accomplished even if the first aid attempts were unsuccessful and the patient died. Most clients will learn from this experience, and are willing to be educated as to how to prevent further losses and avoid future die offs. It is important to discourage the use of poly-pharmacy by the lay person thereby increasing the chances of a controlled application of drugs to succeed. Additionally one of the most frustrating experiences is the outbreak of disease in an established system due to the introduction of a new pathogen through improper quarantine protocols. Often once a system has been managed successfully without major losses or complications, owners forget about all the different problems that could be encountered via new acquisitions. Make sure your clients are reminded on a frequent basis about this issue and educated to practice proper quarantine when adding new individuals to their previously closed colony.


As in other species, in an emergency situation, stabilization is critical for saving the fish's life however the emergency therapy should always be followed by a search for the real problem. A significant percentage of all fish emergencies are related to poor husbandry techniques. Environmental factors are usually implicated in the demise of the patient. The need for a proper quarantine also can not be overemphasized.

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