Safety Precautions for Introducing New Fish to Old Fish

Like any living being, fish are prone to illness at some point in their lives. This section endeavors to explain how to keep fish healthy through proper diet and aquarium maintenance and to how to identify and treat an outbreak of disease.

Receiving tropical fish

It is important to be prepared to receive new shipments of tropical fish. A few simple steps will greatly reduce the chances of fish loss due to stress and disease outbreaks.

The techniques outlined in this guide are the result of many years of research in tropical fish handling, stress reduction, and disease prevention.

The all-in-all technique

Research has shown that all aquarium fish carry a variety of pathogenic bacteria, fungi, and parasites. The aquarium itself also harbors these pathogenic organisms primarily in the gravel bed.

If aquarium fish are healthy, well fed, and have proper water conditions their immune system is able to fight off these ever-present disease organisms.

Newly arrived tropical fish are stressed due to handling and possibly poor water quality in the shipping bags or containers. Therefore, newly received fish should never be mixed with fish already in the store aquariums.

Existing fish should be consolidated into a few aquariums to make room for the newly received fish. This is called the ALL IN/ALL OUT technique. Existing fish are isolated from new arrivals to insure diseases are not spread throughout all store aquariums.

It is far more economical to treat one or two aquariums for disease than every aquarium in the store.

Preparing for new fish

Before new fish arrive, consolidate compatible fish as much as possible. A large water change and a siphoning of the gravel bed is recommended.

The aquarium’s pH level should be adjusted for specific types of fish. Add an aquarium salt to help reduce stress by aiding in osmoregulation, the exchange of oxygen, carbon dioxide, and ammonia across the gill membrane.

Add 1 tablespoonful (20 g) of Aquarium Pharmaceuticals, Aquarium Salt(TM), for each 5 gallons (19 L) of aquarium water. This will aid osmoregulation and ease the initial stress from shipping.

Use stress coat as added protection

Every time fish are netted, their protective slime coating is removed. This natural slime coating helps prevent the loss of electrolytes (salts) from the gills and skin.

Tiny blood vessels (capillaries) lie just beneath the surface of the skin. If the slime coat is removed, essential salts are leached out into the aquarium water. Salt loss can lead to heart failure, muscle spasms, and increased disease susceptibility.

The slime layer also appears to “insulate” the fish from disease organisms. Stress Coat will provide a synthetic slime coat to reduce stress caused by netting and handling. STRESS COAT has been independently tested at the University of Georgia School of Veterinary Medicine and proven to reduce stress in tropical fish. STRESS COAT also contains aloe vera extract that has been proven to aid in the healing of damaged fish tissue.

Add two teaspoonsful (10 ml) of STRESS COAT to each 10 gallons (37.8 L) of aquarium water to protect fish. STRESS COAT also neutralizes chlorine in tap water.

Adjust the water temperature if necessary in the prepared aquariums. Most tropical freshwater fish require a temperature range of 78-82oF (25-28C). Goldfish prefer cooler water, ideally between 68-72oF (20-22C).

Adding new fish to the aquarium

Shipping water should never be added to the aquarium! Water in the shipping bags may contain disease organisms, ammonia, and organic pollutants and must not enter the prepared aquariums.

Pour the fish out of the bags into a net then add the fish to the prepared aquariums. There is no need to add aquarium water to the shipping bag. Fish adjust quite easily to the well oxygenated ammonia-free aquarium as opposed to the acidic, polluted water in the shipping bags.

Immediately remove dead or dying fish. In most cases dying fish will not respond to treatment. If left in the aquarium to die they could possibly infect other fish.


Never allow healthy fish to eat dead fish. This directly transmits disease organisms to healthy fish.

Observe fish closely for 48 hours after arrival. Look for the disease symptoms described later in this guide. For example, if certain species contract Ich (_Ichthyophthirius_), begin medicating as soon as the fish arrive.

Research has shown that most tropical fish carry some type of external parasites. A general anti-parasitic medication such as General Cure(TM) will help to control a variety of external parasites such as gill worms and Ichtyobodo.

Antibacterial medications should not be used unless symptoms appear. Over-use of antibacterial medications has lead to increased resistance of bacterial fish pathogens to medications.

  • Always follow the directions on medication packages. Do not underdose antibacterial medications as it only promotes resistance to the medication.
  • Do not mix two different antibacterial medications together. An antibacterial medication can be used together with an anti-parasitic medication such as General Cure but it is best to treat one disease at a time.

Your past history of shipments will dictate the medication of new arrivals. In some cases you will be able to predict that certain species “always” seem to come down with an infection. Be prepared to treat these fish when they arrive.

Use the following guide to detect the most common symptoms of parasitic and bacterial diseases. Then follow our recommended treatments to help determine the correct medication.

In some cases several medication choices are recommended to treat a particular disease.In these cases select the medications in the order they are recommended. This is because bacterial pathogens are sometimes resistant to one of the medications. If the first medication does not cure the disease it will be necessary to use the next medication listed.