By Peter G. Walker.
Transporting fish or fish eggs from one place to another always carries with it the risk of spreading diseases. Thus as the science of fish pathology has developed, so too has a maze of State and Federal regulations designed to minimize these dangers.
Available treatments for some fish diseases are expensive and often only partially effective; for others such as the viral diseases, no known cure exists. Once a virus has been introduced to a site, a fish culturist has two options: live with the problem or take the station out of production, disinfect and start over with disease-free stock. Either choice is very costly. The alternative is to take the necessary precautions to avoid diseases in the first place.
Fish diseases of State and national concern were, until quite recently, almost entirely those that affect species of the trout and salmon family. Now there is increasing concern in some areas for protection from certain serious diseases and parasites of warm water fishes as well.
The most serious fish diseases are responsible for grave financial losses wherever they occur. Fortunately, wise fish health management assisted by adequate fish importation legislation can effectively minimize spread of these diseases from one area to another.
Legal restrictions faced in transporting fish or fish eggs can vary a great deal, depending on the locale. Federal regulations prohibit importing members of the trout and salmon family (alive or dead) and their eggs unless they have been certified free of two serious disease-causing agents. Individual State fish importation laws, however, range from very strict to none at all. In addition, there is a growing trend towards integrated fish health management of entire watersheds spanning two or more States or Canadian provinces.
It therefore pays to check with authorities before importing or transporting fish and eggs.
Since transporting fish or fish eggs from one place to another carries with it the risk of spreading diseases, a variety of legal restrictions or certification requirements exist to protect fish health. Before any anticipated transfer or importation of fish or eggs, the local fishery agency should be contacted to determine what regulations exist.
Advantages of Eggs
Shipping fish eggs offers some advantages with regard to preventing disease transmission. While viral diseases and at least one bacterial disease are passed from parent to progeny within the egg (vertical transmission), most of the bacterial diseases and virtually all the higher parasitic diseases can be removed from outside surfaces of trout and salmon eggs with an iodine disinfectant.
Two major salmonid viral diseases are endemic to North America: Infectious hematopoietic necrosis (IHN) has, until recently, been largely confined to salmon and trout hatcheries along the Pacific slope; infectious pancreatic necrosis (IPN) is especially devastating in cultured brook trout.
Another serious viral disease, viral hemorrhagic septicemia (VHS), has been con-fined to European trout farms to date. It is of special concern to salmonid fish culturists everywhere since, unlike other viral diseases, it often breaks out in market-sized fish and thereby causes grievous financial losses. VHS is one of the two diseases that is included under Federal Title 50 regulation, a legislative mandate requiring certification on salmonid importations into the United States.
Main State Action
State regulations regarding bacterial fish diseases are most often confined to furunculosis, enteric redmouth disease and bacterial kidney disease. All three pose an economic threat to salmonid growers.
Furunculosis and enteric redmouth disease are caused by Aeromonas salmonicida and Yersinia ruckeri respectively; both pathogens can be effectively disinfected from egg surfaces. Renibacterium salmoninarum, the causative agent of bacterial kidney disease, is transmitted vertically within the egg and should therefore be given special consideration when planning shipments.
Among the higher parasites, the myxosporidian protozoan Myxosoma cerebralis,causative agent of whirling disease, is often considered the most serious danger from fish importations. Endemic to Europe, this internal, cartilage-destroying parasite became established in the United States in the late 1950's and has since spread to a number of States, although in most cases those with enforced importation laws have successfully remained free of the organism.
M. cerebralis is the second pathogen (along with VHS virus) for which inspection is required by Title 50 regulation before importation into the United States. Some other serious parasites frequently specified in interstate or inter-drainage shipment requirements include the myxosporidian Ceratomyxa shasta, digenetic trematode blood flukes of the genus Sanguinicola and the Asian tapeworm Bothriocephalus opsarichthydis.