Tropical fish, like most living organisms, are subject to various types of disease. Dr. Ross F. Nigrelli of the New York Aquarium has made a complete study of those factors that affect fish in captivity. Dr. Nigrelli lists the following factors that he believes account for the loss of fish in captivity; and your custom fish tank makes no exception:
1. CROWDING. A given aquarium will support only a certain number of fish before they will turn against each other in an effort to reduce their density. More carbon dioxide will also be present in the water and thus further add to the destruction. Diseases that are infectious will be more easily spread in the smaller tanks.
2. TEMPERATURE. Temperature fluctuations must be kept to a minimum. Though many fish have wide ranges of tolerance, successful adaptations to temperature changes require a long period of time. Higher temperatures may activate certain types of parasites, while lower temperatures might cause them to encyst (encase themselves and become inactive).
3. LIGHT. The fish generally kept in home aquaria are tolerant of a wide variety of light conditions. The quality—natural daylight, incandescent, or fluorescent—and quantity—providing they are not kept in total darkness or semidarkness for more than about two- thirds of the time—seem to make little difference to tropicals’ well-being. The direction of light is important, however; most aquarists agree that artificial side lighting is detrimental. In other words, all artificial lighting should come from above the water’s surface. Indeed, it is claimed that the best natural illumination also comes from above. It is widely believed that the principal reason fish in captivity spawn most frequently in the spring is because of the increasing length of daylight most apparent at that season. Certain types of flatworms (Trematoda) are phototropic (attracted to light) when in the larval stage. These trematodes, especially the gyrodactylids, cause very nasty diseases of the skin and gills.
4. pH OF THE WATER. The most suitable pH (acidity or alkalinity) of the water is variable for individual types of fish. Marine fish require a pH of about 8.0, slightly alkaline, while most tropicals require a pH of about 7.0, neutral. Most species of fish when kept in a tank of their own will tend to keep the pH of the water at the most desirable level.
5. SPECIFIC GRAVITY OF THE WATER. Specific gravity (s.g.) may be defined as weight per unit volume as compared with an equal volume of water. The specific gravity of water is 1. Should water get heavier from an increase in dissolved substances it would increase some of the chemical changes that take place within the bodies of the fish. For example, their breathing would get more rapid. An increase in s.g. has a harmful effect upon many parasites in some instances.
6. FLOW AND AERATION OF WATER. Several gases are toxic to fish when they reach a certain concentration. Various fish require different amounts of aeration to rid the water of gases such as carbon dioxide, hydrogen sulphide, and nitrogen.
7. METABOLIC WASTE PRODUCTS. Water contains many types of matter dissolved in it. Some of this material comes from the waste excreted by the fish. Certain types of this material are beneficial to some fish, but too strong a concentration is undoubtedly not good.
8. DIET. Many fish get poor diets and may suffer from various deficiencies. Liver and kidney troubles are frequent manifestations of vitamin deficiencies.
9. HANDLING. Many fish get scratched or lose a few scales when being handled. These openings are often sites of attack by harmful organisms.
10. PARASITES. Certain types of organisms attack the fish and live on them. Some parasites will attack only a specific fish, but there are many types of fish parasites that show no specificity. These types are the most dangerous.
Certain different types of ailments may be treated by the same methods, but there is definitely no “cure-all” for fish. Many types of medicines sold as cure-alls should be ignored. About the only medication that can be offered many ill fish is a bath in a gallon of water containing about 2 12 tablespoons of plain household salt. The temperature of the water should then be raised so any encysted parasites may become active. It is wise to treat the whole tank with this salt treatment. Most diseases of fish are very infectious, and salt is the best type of nontoxic medicine to be recommended.
The widespread Ichthyophthirius, a type of protozoan parasite causing “ich,” is very successfully treated this way. The white spots, which usually indicate the presence of ich, are the encysted parasite. A rise in temperature in this case is needed.
This is a slightly edited & updated version of an article originally published on “Fish-Aquariums.net”