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<The following is a "position paper" I produced for a college seminar class (Parasitology of Fishes, Dr. Olson), back in Fall of 1976. Though dated, the same principles apply today>
I. Considerations- What is a cultured fish, parasite, disease, infection
II. Disease differences in cultured vs. wild fishes
D. General Stress
III. Immunity and the environment
IV. Disease prevention and the environment
A. Maintaining proper conditions
B. Preventing introduction of infectious organisms
C. Sterilizing water, ponds
V. General fish pathology- disease detection
VI. Treating diseases
B. Biological control
C. Physical-mechanical control
D. Chemical control
VII. Problems in disease- discussion
What is a cultured fish? Any produced, grown for food, sport or aesthetic purposes. The current list includes several hundred species, but principally involves a few dozen as most important, particularly some cyprinids, salmonoids, acipenserids, ictalurids, silurids, pangasiids, mullets and milkfishes as food fishes, and dozens of other cyprinids (minnow-sharks, barbs, danios, rasboras), characiforms (tetras), callichthyids, loricariids, several South American and African cichlids, clownfishes, dottybacks, neon gobies... My discussion will largely involve examples of these aquatic-source protein and tropical ornamental fish groups, as well as pond rather than open-water (e.g. sea-ranching) culture.
A parasite may be defined as any organism living in or on another species where it obtains it's nourishment (plant or animal) and perhaps protection.
Disease is any departure from health; for our purposes as related to infection or infestation by other organisms, i.e. parasites. Limited reference will be made to infectious diseases "caused" by viruses, bacteria, fungi, algae and parasitic diseases caused by protozoa, helminths, arthropods and other metazoa.
A parasitic infection-infestation may be:
A) Pathogenic- disease producing
B) Latent- only mildly infectious. A situation where the fish has more or less reached an agreement with it's parasites due to natural or acquired immunities. It's important to remember that many parasites, viruses, bacteria, funguses, protozoans, helminths and arthropods are very often present with a cultured fish species. If a healthy, stable environment deteriorates, dissolution of immunity follows and a latent infection becomes pathogenic (Spotte, 1973).
Diseases in wild and cultured populations of fishes by be caused by pathogenic organisms, effects of toxic materials, or general environmental deterioration. Because all three groups of these factors operate together they will be discussed together as they relate to parasitic diseases of cultured fishes.
II. Disease differences in cultured vs. wild fishes
As Bauer (in Dogiel et al. 1970) points out, there are several major differences, positive and negative, between pond-cultured and non-pond cultured fishes, their disease control and prevention. Generally the number of parasite species is lower but due to the conditions of culture their numbers may be high and disease etiology altered. These differences may be explained by consideration of the design of culture systems vs. wild environments.
A) Density- Due to the proximity of conspecifics, transmission of parasites is facilitated. Also, very little is known re the social, pheromonal effects of crowding.
B) Confinement- The uniformity of a culture environment in terms of temperature, pH, oxygen concentration, food availability, and other physical-chemical-nutritional factors allows little latitude for cultured fishes to select more suitable conditions.
C) Monoculture- The cultivation of one or perhaps a few species in a system that is periodically sterilized, otherwise chemically treated negates the presence of intermediate hosts and vectors. Consequently, most systems harbor a smaller number of parasites than natural waters. Parasites with complex life cycles, such as flukes, tapeworms, thorny-headed worms and roundworms are rare, whereas protozoans, some leeches and copepods with direct life cycles are common.
D) General stress- Disease in fishes can be a physiological response to stress (Gratzek, 1975). Some common sources of stress are transportation, excessive handling, abrupt temperature fluctuations, physical-chemical factors, and overdosing with medicants. Many fishes die outright from severe stress but many more often from chronic less-severe stresses. Many fish pathologists feel that fish carry bacteria and protozoans in low numbers in their blood and kidney tissues as well as on the surface of their skin and intestines, but remain healthy until stressed.
III. Immunity and the environment
There are three general sets of considerations to the well-being of any cultured stock:
1) Initial state of health, genetic and developmental
2) Suitability of the environment (chemical, physical, nutritional, social...)
3) Virulence of present pathogens
Fish stocks are selected and bred for traits which insure greater resistance to the stresses of culture, including disease control. Many viral, bacterial and parasitic diseases have been selected against by genetic engineering. Recently (1975) there has been established a Fish Genetics Lab of the Bureau of Sport Fisheries & Wildlife in Beulah, Wyoming (Anderson 1974).
It's been mentioned that as regards disease-causing organisms the physiological condition of the hosts determines whether they remain latent. Such factors as oxygen concentration, carbon dioxide concentration, unionized ammonia presence, organics and heterotrophic bacteria accumulation may shift the balance of health-sickness. Very often outbreaks, particularly bacterial and protozoan infections are the result of a decline in water quality or inadequate nutrition (Spotte, 1970). Pollutants are receiving more and more attention (Vernberg et al. 1977). Temperature fluctuations and high toxic metabolite levels are two most cited causes for epizootic outbreaks in established systems.
IV. Disease prevention and the environment
Most preferably and often the only way to eradicate parasitic diseases by prophylactic measures. Spotte (1970) lists four factors involved in environmental disease prevention:
1) Maintaining proper environmental conditions
2) Preventing introduction of outside infectious agents
3) Sterilizing circulating culture water and systems
4) Adequate nutrition
1) Proper environmental conditions are species and strain specific. For all factors there are optima and ranges for parasites and hosts. What is done is basic environmental manipulation to favor the host.
2) Many fisheries try to comply to the guidelines Dogiel et al. (1970) propose: that of naturally clean water of proper temperature, etc. running into and out of each system separately. Water from sterile sources is preferable, but rarely available. Often it is more economical to use other sources. The method of treating recirculating water (closed systems) described by Spotte (1970) is often used due to the unavailability of consistently good water.
A) Rapid sand filter- removes large infectious organisms
B) Diatomaceous earth- removes most bacteria, protozoans
C) Darkened storage vats- to store water for two weeks, later aerating it, causing death, lowered virulence of many parasites due to lack of hosts
D) Sterilizer- ozone or ultraviolet
Prefiltration involves a routine of chemical sterilization, drying of filters immediately after processing a batch of raw water.
Quarantine- new stocks should not be added to main systems until they have been isolated, treated by dips, inoculation, etc. and thoroughly checked to insure they are disease-free. All nets, equipment used with these stocks must be sterilized after use or used only for these fishes/systems.
Live foods- there is always a risk with live foods, even if tank raised, of introduction of disease organisms. In general it is safe to fed freshwater foods to marine fishes and vice versa, e.g. Artemia, Daphnia. Most commercially prepared foods are preferable to live or frozen from the standpoint of disease transfer.
Intermediate hosts; destruction of snails, leeches, copepods, etc. and wild fishes which may act as carriers or reservoirs is often done (Bauer 1973).
3) Sterilizing circulating water is accomplished much as described above for raw water. Generally ponds and tanks are completely dried on a regular basis and sterilized with strong bases, bleach...
4) Nutrition- a proper discussion is beyond the scope of this paper (please see here: http://www.wetwebmedia.com/feeding.htm). Considerations such as chemical balance, storage, amount, frequency and application method are important to parasite control.
V. General fish pathology
Identification of pathological signs and symptoms and their possible causes requires a knowledge of normal fish anatomy, physiology and behavior, such as habits and postures, swimming, rate of respiration and movements, color changes, feeding habits, growth abnormalities. A good review of fish pathology is Amlacher (1970) and Reichenbach-Klinke (1973).
Fish may be anesthetized or sacrificed. Procedure then is to examine microscopically and macroscopically the exterior, skin, gills, abdominal cavity, gonads, digestive tract, liver, gall bladder, pancreas, spleen, kidneys, swim bladder, heart, blood, skeleton, nervous system and sensory organs, eggs and fry if present.
A practical method of assessing stress in fishes using "stix", commercially available plastic strips applied to fish mucus to determine the presence of hemoglobin is described by Ramos and Smith (1978). Also mentioned as a chemical assay indicator in the literature is blood sugar levels.
A) Considerations- prophylaxis is preferable to treatment, but oftentimes inadequate.
Much care must be exercised when treating diseases of cultured fishes; often the cure can be worse than the disease, especially if stable environmental conditions can't be maintained. In many cases it is best not to treat animals infected by bacteria or protozoans as these losses can often be traced to improper environment. Generally the most infected stocks are removed and the problem/s corrected. (Taylor & Muller 1970).
Helminth and arthropod parasites have greater resistance to immune responses of the host and must be treated differently. Often a chemical must be applied and the culture system sterilized by drying or chemical poisoning (e.g. formalin, chlorine, lime). These infections are rare if water quality procedures are closely followed.
As usual, cost-effectiveness must be considered.
Types of controls may be divided into biological, physical, and chemical in order of preference by most workers (Mawdesley-Thomas et al. 1974).
1) Predation- certain organisms feed on intermediate hosts of parasites. Some examples are the red ear sunfish (Lepomis microlophus) that eats snails, the protozoan (Amphileptus voracus), that feeds on other (parasitic) protozoans, Chaetogaster sp., an oligochaete worm, feeds on snails.
2) Cleaning symbiosis- known mutualistically symbiotic cleaner fishes and shrimps are used in the pet-fish interest as biocontrols.
3) Physical controls- includes such things as increasing flow rate, filtration, sonic vibrations, photoperiod and strength, pH, UV light sterilization, surgery (brood fish) and temperature manipulation. There are often differences between ideal temperatures and ranges for hosts and parasites, such that by raising or lowering one may be selected for. Anthony (1969) observed that raising temperature from 12 to 20 C. resulted in the disappearance of Gyrodactylus elegans on the goldfish, Carassium auratus. According to Lom (1969), the protective capacity of the mucus of carp infected with trichodinids is manifested only at elevated temperatures.
4) Chemical control- generally considered a last line of defense, prophylactic use of chemicals is often important in North American fisheries during March through July when parasitism is highest, resistance lower, and fish and parasite reproduction coincides. Inspection and treatment are scheduled using temperature as an indicator. (Herman 1970).
Degree of success in using a compound is related to water chemistry, temperature, pH, salinity substances with synergistic and antagonistic effects, formulation differences and methods of application; the susceptibility of fishes to toxicants is affected by their developmental stage, physiological condition, age, size and sometimes sex. Species, subspecies, and strain differences may be profound, so effect determinations must be exact (Hoffman 1974).
When selecting a medication several factors should be kept in mind.
1) The medication should be "quickly" degradable; many have residual effects.
2) The compound should be as specific as possible; few are.
3) It should have as little deleterious effect on beneficial microbes, e.g. filter bed, as possible.
4) It should cause as little stress to the cultured species as possible. Several compounds, e.g. heavy metals, cause fishes to shed lots of mucus; this should be avoided as the mucus serves several vital functions (please see here: http://www.wetwebmedia.com/fbodyslimfsh.htm); defense against invasion, attachment of ectoparasites, involvement in gas exchange and osmotic balance. Fish mucus contains parasitic protozoan repelling antibodies (Lom 1969).
5) Laws- FDA requires extensive testing of any chemical agent before it can be used on a sport or food fish. Other countries have even stricter laws.
Often used chemicals:
Formalin continues to be a mainstay for the prevention and treatment of external protozoans and monogenetic trematodes. There are lots of cautions on use re temperature, oxygen levels, etc. This material is best used as a flush.
Malachite green is the only other chemical used widely in the U.S. for the treatment of fish parasites (Herman 1970). Calomel and Carbersome are no longer widely used; they are toxic and carcinogenic. Enhaptin and Cyzine are suggested for hexamitiasis. Di-n-butyl tin oxide has replaced Kamala as a vermifuge. Gammaxine (benzene hexachloride, BHC) is used for the treatment of parasitic copepods; Dylox (Dipterex, Neguvon... please see here: http://www.wetwebmedia.com/PondSubWebIndex/contrpdparasit.htm) is preferred by others. Quinine is limited to use in aquaria. NaCl, copper sulfate and potassium permanganate are highly toxic to some species.
E) Methods of application
Diseased animals generally should not be treated directly in the culture system with chemicals. Many substances such as antibiotics and formalin interrupt nitrification, so treatment tanks use physical and chemical methods, e.g. carbon filtration, air-stripping with ozone for ammonia conversion, and not bio-filtration (Mawdesley-Thomas 1972).
Several methods of application are used. The most common method of administering therapeutic agents to fishes is bathing them in water-soluble compounds. Variations are dips, short baths (1 hour), flush (flow through), long bath or constant flow of drug. Oral-medicated feeds are widely used to administer drugs to fishes for systemic infections. Injection of large numbers of fish is time-consuming and stressing to livestock. Small numbers of valuable fish may be treated this way. Topical-wounds and localized infections of valuable fish are sometime treated with topical applications.
VII. Problems in disease- discussion
Treatment of parasitic diseases is largely limited to those occurring on external surfaces and the intestinal lumen. Blood parasites and encysted worms can't be treated effectively and economically at this time. Treatment of intestinal parasites must be accomplished orally.
There are many serious parasitic disease w/o cure. We need a drug badly in the fish industry that will treat for both protozoans and gill and body flukes for instance.
Other major deficiencies in the field are lack of people who can make accurate diagnoses, low availability of cures, and lack of knowledge re life cycles, physiology and ecology of fish parasites.
Amlacher, E. 1970. Textbook of Fish Diseases. Transl. by D.A,. Conroy and R.L. Herman. TFH Publ. Jersey City,
Anderson, D.P. 1974. Fish Immunology. TFH Neptune City, New Jersey.
Anthony J.D. 1969. Temperature effect of the distribution of Gyrodactylus elegans on goldfish. J. Wildlife Disease Association.
Bauer, O. 1973. Diseases of Pond Fishes. Transl. by A. Mercado. Israel Prog. for Scientific Transl. Jerusalem.
Dogiel, V.A. Petrushevski, G.K. & Yu. I. Polyanski. 1970. Parasitology of Fishes. TFH, Great Britain.
Gratzek, J.B. 1976. Stress in fish. Pets/Supplies/Marketing 30:2
Herman, R.L. 1970. Prevention and control of fish diseases in hatcheries. In: A Symposium of the Am. Fisheries Soc. on Diseases of Fishes and Shellfishes (S.F. Sniezsko, ed.) Am. Fisheries Soc.., Wash. D.C.
Hoffman, G.L. 1974. Parasites of freshwater fishes; a review of their control and treatment. TFH Publ. New Jersey.
Lom, J. 1969. Cold-blooded immunity to protozoa. In: Immunity to parasitic animals, vol. 1. G.J. Jackson, R. Herman and I. Singer (ed.s). Appleton-Century-Crofts, New York.
Mawdesley-Thomas, L.E. 1972. Diseases of Fish. Academic Press, London.
Mawdesley-Thomas, L.E., K.W. Burris, J.L. Knuckles et al. 1974. Diseases of Fish. MSS Info. Co., New York.
Ramos, F. & A.C. Smith 1978. The C-reactive protein (CRP) test for detection of early disease in fishes. Aquaculture, 14 (1978).
Reichenbach-Klinke. 1973. Fish Pathology. TFH, New Jersey.
Spotte, S.H. 1970. Fish & Invertebrate Culture, Water Management in Closed Systems. Wiley-Interscience, New York.
Spotte, S.H. 1973. Marine Aquarium Keeping, the Science, Animals, and Art. John Wiley & Sons, Inc.
Taylor, A.E.R. and R. Muller. 1970. Aspects of Fish Parasitology. Blackwell Scientific, Oxford.
Vernberg, F.J., A. Calabrese, F.P. Thurberg, W.B. Vernberg. 1977. Physiological responses of marine biota to pollutants. Academic Press Inc., London.
FAQs/Input re Parasites and ornamental aquatics business:
Treatment of Ich in Retail System
commercial holding tank questions; Crypt...
Alternative treatment for a common marine parasite... Commercial Crypt remedies, prevention - 07/19/08 Hello, I was wondering if anyone on the team has had any good experience with giving a marine fish with crypt a freshwater bath in place of a more 'solid' technique, such as copper treatment or hyposalinity (not that hypo is Bob's favorite)? <Some folks report success with such... perhaps their trials involve fishes with only superficial infestations... maybe these are principally only symptomatic...> I'm more of a Cupramine guy myself (in a separate treatment tank), but it seems my employer would like me to use freshwater baths exclusively in the main display / selling tanks which also house invertebrate life. <Mmm... I strongly suggest that they, you do a bit of further considering here... I would do FW baths on arrival (pH adjusted, with formalin if a commercial setting)... and even better to best, keep all incoming fish livestock quarantined for a few weeks before showing, offering it to the public... I would NOT mix fish and invertebrate livestock in a wholesale or retail setting... period> No option for separate treatment in a different tank. So while not my favorite option it will probably still give results and just wanted to fine tune it with some input. If you could tell me your frequency of the bath, duration of the bath you find effective. <Won't be... like the idea of invading countries, murdering their citizens to "make people free", this idea is contrary to reality. How to put this another way... it won't work> And if you combo it with gravel vacuuming - water change, the frequency and percentage of water changed. If you use any other methods with it such as melafix <... API should be sued back to the stone ages for this and other faux products and their promotion. Really. Have stated this often and loudly enough. This product is garbage> for bacterial infections of crypt wounds or cleaner gobies / shrimp to lending a helping hand, or anything else which might contribute to a recovery. <All this is gone over and over on WWM> I was considering fw bath repeated daily for 14 days, <... no... too much time, trouble, and stress on the fish livestock. Ridiculous> 7 min duration, gravel vacuuming bottom of tank 5 gallons out of 60 every fourth day or so, melafix dosed daily, <Please...> few cleaning shrimp there for luck. <Don't rely on luck...> Considering use of a U.V. sterilizer instead of melafix, but not likely. Trading out treatment of secondary infections for a unknown increased destruction of the parasites free swimming stage. experience and suggestions appreciated, and thank you for your time, Jonathan <Thank you for sharing Jonathan. A note to browsers through time... this is actually an indicative case, window into the thinking, operation of the trade... A reminder that many folks, though honest, of good intent, don't really know much re the science of actual husbandry of ornamental aquatics. Bob Fenner>
System for Fish at new facility ( Emergency) 8/28/05 Hi Bob and Team <Hello> This is a desperate cry for help.....I have previously written asking for advice on my system for livestock (fish) <I recall> I thought I had it made....following all your guerilla acclimation procedures.... had minor cases of ich and Velvet but got rid of those effectively, and had no problems with them since....... Now I have the Mother of all major problems.....I have over 50 Queens, French, and some additional red Sea fish in stock......I have confirmed that ...I have a bad outbreak of Brooklynella <Through what observation, tools?> ......I sort of identified it a few days ago, and we have been doing 8 minute pH adjusted Freshwater baths with Formalin... <... and moving the dipped/bathed fishes to another non-infested system...> also added Methylene Blue today to the dip.......but.....I am super concerned about the next 48 hours. I removed all Cupramine with Cuprisorb....changed 50% of the water.....I possess 3/4 of an ounce of 37% Formalin...and the supplier is closed till Monday......hmmmm It's late at night here, so I hope I didn't make the wrong call by adding the Formalin to the system ( 1250 gallons)... <Very dangerous> I guess it is way below the recommended dosage for hospital tanks, and I also know you don't recommend it in the display tanks....Is there anything else I can do???? <... not enough data... re your systems...> I have some Hospital tanks, but not sufficient for all of these fish.....They are still eating , but less...are really twitchy, and today was the day they became pale. <Very bad> I used to deal with Ken at Yankee Divers, and got great fish from him...He was just about to let me in on how he had used Formalin for years, starting with very, very small amounts... <Very small> in his main system....Anyway, he sold out to a guy who has since lost me more money than I would like to admit by sending sick fish, and incomplete orders.....He also sent me 50 Turbid Flames, on the one day I was off work this year......and they spent 24 hours in my system....half were dead by then, and the other half I ordered dead ( feel guilty, but didn't want to prolong their agony).. That was a month ago...my Brazil shipment arrived 2 weeks ago. Anyway Ken said that his Bio-towers had over time become "immune " to using Formalin.....is there any truth in this? <Some> ...and....what can I do, if anything now?...as I am in danger of a big die-off in the next 48 hours looking forward to some solid advice.... JD <... we need to "start at a/the beginning"... know what you do on receiving, your systems... At this point, I would increase aeration, circulation to the maximum... NOT put any more formalin in your systems, monitor ammonia... be ready with water to change most all out... Get a microscope! BobF>
Re: System for Fish at new facility ( Emergency) 8/28/05 Hi
Bob....thanks for the swift reply.......Observation?....well I have
some books on the subject, and also spent a long time reviewing your
site and others....The fish started scratching a little a couple of
days ago, but only around the gill areas....the other signs
were the twitchiness, followed by this scratching, a white
mucus forming on 1 eye, followed by listlessness, losing
their appetite, the whitish areas appearing, and now the "looking
for air"......Also, the failure of Copper to do anything
positive...... <All indicative, especially the last... though there
are still a handful of genera, species of protozoans this might
otherwise be... real trouble...> I have sufficient room for a couple
of dozen fish in Hospital tanks, but not 60 or 70 My water parameters
are perfect, and monitored every day. <I suspect/ed as such... the
problem is the state of the folk's ahead of you... what were their
systems like?> And I do have 800 gallons of water on
standby, as well as Seachem AmGuard concentrate. All the
details of my system are in the attached emails <Good> I
certainly shall have to get a microscope.... <Yes> Do you have
any ideas what would be a good thing to do now?? JD <Yes... add
aeration, lower specific gravity... a few thousandths a day by adding
freshwater... to about 1.017-1.018 (almost always a good change with
marine parasitic infestations), look into that microscope, Ed
Noga's works... Bob Fenner>