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Methods of reproduction vary - range from oviparous (egg layers) to viviparous (live young producers). Generally, viviparousity entails internal fertilization and oviparousity means external fertilization. Freshwater fishes are usually oviparous. In referring to the latter, there are two forms: in the first, there is no cyclic reproductivity - the male and the female die after spawning. In the second, cyclic changes occur and both adults live after spawning.
Eggs tend to be demersal (sink), sticky, or non-sticky (float). Young are called fry.
well aerated water of a good quality is most important. Oxygen content depends on surface area of water. Temperature control, removal of wastes, lighting, and vegetation are also important. Size of aquaria depends on species. Paint bottom of tank - fish do not receive light from below. Clean according to schedule.
Fish become conditioned to consistency of food. Abrupt changes in diet are stressful. Natural food organisms should not be used. Commercial diets should have accompanying analysis. Feed adults daily and only as much as can be eaten within 10 minutes.
Same criteria apply for aquaria. Periodic checks must be made on the water to check for salinity. Water should be added on a routine basis to prevent a build-up in salts. Water can be taken from the ocean or "brewed" at home.
Based on trial and error and depends on species. Commonly fed items are shrimp bits, squid, guppies, and brine shrimp. Feed twice daily and remove after 10 - 15 minutes.
12.5.1.1 Piscine Tuberculosis: [Has zoonotic significance]
Tuberculosis in fish is often caused by Mycobacterium fortuitum or M. marinum. Some authorities estimate that up to 30% of aquarium fish may be infected. Signs vary from none in asymptomatic carriers to severe emaciation and anorexia in those with overt disease. The bacterium causes development of yellow-white gray nodules which are widespread throughout the body. The organisms are shed in feces or from skin lesions. It is ingested and a compromised host may then become infected. The spread of tuberculosis is favored by overshocked tank conditions and poor water quality.
This is an incurable disease and fish which fail to respond to treatment for other conditions should be removed from contact with other fish until one can rule out tuberculosis.
12.5.1.2 Aeromonas spp. Infections:
Aeromonas hydrophila, A. pemctate, and Pseudomonas spp. may infect fish and cause a septicemic infection. Sign include reddening at the base of the fins and tail and around the anus. Ascites will often develop giving the fish a bloated appearance resembling dropsy (discussed later).
These are opportunists and cause disease only in the compromised host. The conditions which favor their virulence are many which decrease water quality such as build up of organic substances causing low oxygen concentrations.
Treatment requires larger water changes and high levels of antibiotics for 5 to 7 days. Tetracycline, chloramphenicol, kanamycin, gentamicin can each be used singly at the rate of 250 mg/5 gallons of water in the tank. The dosage of tetracycline may have to be increased two to three times, especially if it has been used before. Furanace is sold for use in aquariums at a rate of one 3.8 mg capsule per 10 balloons of water. It may be the most effective treatment to use. Partial water changes (25%) should be made before the daily treatment. These antibiotics may damage plants and the biological filtrations system. Activated charcoal may filter the drugs out of the water. Organic materials will bind the antibiotic. It is recommended therefore, that treatments take place in bare all glass tanks. All treatments should be continued for 5 to 7 days, and at a temperature of at least 75 F to allow the fish to properly metabolize the antibiotics. Maintain vigorous aeration during treatment.
An excellent adjunct or primary treatment, if the fish are still eating well, is to shake the powdered antibiotic onto food and thus induce the fish to ingest more drug that it normally might. The tank treatments rely on the fish absorbing large amounts of water. All of the listed drugs except Furanace can be used in this matter.
12.5.1.3 Columnaris Disease:
This is caused by Flexibacter columnaris. Signs are reddened ulcers on the lips and skin. This is an opportunist whose virulence is favored by higher tank temperature. It gains entrance via the wounds. It can be effectively treated by penicillin baths (40,000 to 160,000 I.U. per gallon) or any of the treatments listed for Aeromonas spp.
12.5.1.4 Dropsy:
This disease is caused by a variety of agents. The affected fish will have swollen abdomens and the scales protrude giving them a "porcupine" appearance. The dwarf gourami (Colisa lalia) seems to be particularly susceptible to this condition, especially if exposed to sudden temperature changes. Treatment is not usually effective. May use Antibiotics, as for Aeromonas spp.
12.5.1.5 Bacterial Gill Disease:
This is a disease complex frequently reported in young salmonids and aquarium fishes. It is initiated by crowding and poor quality water including organic overloading, high ammonia levels and silt. Opportunistic bacteria such as Flexibacter, Aeromonas and Pseudomonas spp. traumatize gill tissue. There is respiratory problems, swollen gills, and may see mottling with patchy areas of bacterial growth. Treat secondary bacterial infections by the antibacterial drugs. Control is by avoiding overgrowing and improving water quality.
12.5.1.6 Furunculosis:
The causative agent is Aeromonas salmonicida. It causes 'furunculosis' in salmonid fish and 'ulcer disease' in gold fish. In acute form; hemorrhages are found in the fins, tail, muscles, gills and internal organs. In the chronic form; focal areas of swelling, hemorrhage and tissue necrosis are seen in the muscles. Treatment can be attempted using Sulfamerazine at a dose of 200 mg per kg of fish weight for 14 days. Drug should be discontinued 21 days prior to human consumption.
12.5.1.7 Vibriosis:
It is caused by Vibrio anguillarium and other Vibrio spp. The infection is common in marine fishes and is less common in fresh- water fishes. The organism produces systemic manifestations including hemorrhages and ulceration on the skin, fins and tail, and hemorrhages and degenerative changes in the internal organs. Treatment is by Sulfamerazine at the rate of 17 g per 100 kg of fish for 10 days. Must withdraw drug 21 days prior to human consumption. Preventive vaccination with formalin-killed Vibrio is now used commercially.
12.5.2.1 Infectious Pancreatic Necrosis: [Unclassified virus]
Infected fish usually swim in frantic or spiral manner. Transmitted in sperm, feces and eggs. Survivors serve as carriers. No treatment.
12.5.2.2 Lymphocystis Disease:
[Iridoviridae, DNA virus, produces intracytoplasmic inclusion bodies.]
Granular wart-like lesions are seen on the fins occasionally on the body. Intracytoplasmic inclusion inclusion bodies are seen.
12.5.2.3 Fish Pox:
[Poxviridae, DNA virus, produces intracytoplasmic inclusion bodies.]
Pock lesions are seen on skin, fins and eyes. Intracytoplasmic inclusion bodies are seen.
12.5.2.4 Viral Hemorrhagic Septicemia:
[Rhabdoviridae, RNA Virus]
Kidney swelling and liver degeneration are seen on postmortem.
12.5.2.5 Other Viral Diseases:
- Chinook Salmon Virus
- Sockeye Salmon Virus
- Infectious Abdominal Dropsy
Treatment for viral diseases is difficult. Temperature manipulation is helpful. Sanitation of the tank is best method to control the viral diseases in general.
12.5.3.1 Branchiomycosis: [Gill Rot]
Gill rot is caused by Branchiomyces sanguines and B. demigrams. It is an infection of the gills. The gills become swollen and dull gray to brown. The fish breathe more and more rapidly as the disease progresses. If the specimens of the gill is squashed between two glass slides and examined microscopically, the fungal hyphae can be seen. Low oxygen levels, low pH, and warm temperatures (25 to 32 C) favor the virulence of this opportunistic pathogen. There is no effective treatment.
12.5.3.2 Saprolegniasis:
The etiologic agent in this disease is Saprolegnia spp. It is an opportunist that mainly infects wounds. It appears as white to gray, cottony growth on the wound area. Their hyphae are easily visualized microscopically on wet mount preparations.
It must be differentiated from the hazy gray-white mucoid material which accumulates normally on wounds.
This infection responds to the topical antifungal treatments if they are initiated before the viable, deeper tissues are invaded. Mercurochrome, copper sulfate, potassium permanganate, or tincture of iodine can be daubed onto the affected areas.
Dead eggs are frequently attacked by Saprolegnia, so they should be removed to prevent the fungus damaging nearby eggs. This may be prevented by incubating the eggs with methylene blue. A stock solution is made by dissolving 1 gram of methylene blue in 200 ml of water. A 3cc of this solution is placed in 2.5 gallons of tank water. A one hour bath in copper sulfate or malachite green solutions at rate of 5 ppm, or a 15 minute bath in a 1:500 formalin solution (2000 ppm) may also effectively be used. These treatments can be given daily until the fungus is controlled, but should not be used close to hatching time.
12.5.4.1.1 Whirling Disease: [only reportable disease to Fish & Wildlife Commission, U. S. Department of Interior]
This disease is caused by Myxosoma cerebralis. These parasites are found in the cartilaginous portion of the head, and vertebral column, with resulting skeletal malformation, granulomas and necrologic damage. The nerve that controls the equilibrium (melanophores) of the posterior body, and the auditory (hearing) nerves are often damaged. There is a loss of control, (as the parasite causes necrosis of the cartilages). Fish whirl and chase their tails. Treatment involves addition of malachite green, salt, methylene blue or acetic acid to the tank has been proven effective.
12.5.4.1.2 . White Spot Disease: [Ich, Ick]
Ichthyophithirius multifiliis is known to cause this disease. It is the most common and is the largest protozoa infecting fish. It appears as "white spots" on the skin. Afflicted fish scrape against aquarium objects due to skin irritation. If the gills are heavily parasitized, the fish will show rapid breathing due to hypoxia. Scraping of white spots and examining under the microscope will reveal the parasite which has a prominent "c" shaped nucleus.
The parasite has three stages in its life cycle:
- (1) encystment on solid substrate (trophont),
- (2) free swimming (tomite) stage, and
- (3) encystment in dermis of host.
The speed of the cycle depends on temperature. Only the free swimming stage can be killed easily. Treatment requires raising of tank temperature to 80 F to speed up the life cycle and the addition of medication to the tank water. Many commercial preparations are available. The old standby is malachite green. One gram of malachite green-oxalate is dissolved in 1 liter of water. Two ml of this solution is added to 100 liters of aquarium water. Treatment is repeated on days, 3, 5, and 7. Activated charcoal filtration should be discontinued during this time. Formalin at a concentration of 15-20 ppm can be used singly or in a very effective combination with malachite green for stubborn cases.
12.5.4.1.3 Velvet or Rust:
The etiologic agent is Oodinium spp. The skin will be covered by a gray to yellow velvety coating or have multiple discrete white spots similar to those seen with "ich."
The same treatments as those for "ich" will also work for velvet disease. Many of the freshwater Oodinium spp. are susceptible to high salt concentration. Add one-half to one teaspoonful of aquarium salt to the water for prevention. This is a welcome by most fish. Cooper sulfate is considered to be the most effective treatment. Therapeutic level of free copper ions is 0.15 ppm for 2 weeks. Copper sulfate will also kill invertebrates, algae, and the aquatic plants.
12.5.4.1.4 Other External Protozoa:
Many other protozoa infect the skin of fish. Fish are most susceptible to infestation when they are stressed. Signs are similar in most infections and include "flashing" (rubbing against objects and exposing light colored belly), hazy mucoid coating of skin, rapid breathing of gills are involved, and decreased appetite. Therapies listed for Oodinium spp. or "ich" will also work on these infestations. Many good commercial preparations are available. Always follow label directions.
12.5.4.1.5 Hole-in-the-Head Disease:
This disease is caused by Hexamita spp. Angelfish are considered to be the most resistant and African chichlids and Discus fish are the most susceptible. This protozoan infests the gut and can penetrate the intestinal wall to invade other tissues. They will cause pitting ulceration of the skin, which is often most noticeable on the head. Fecal material will form white-thread-like strands which stream from the anus. The flagellated parasites can be detected microscopically in the feces. The fish become anoretic, emaciated, and eventually die. Metronidazole (Flagyl ) is the drug of choice for treatment: 250 mg/5 gallon of water as a bath every other day for 3 treatments and concurrently orally in food as 1% of ration for 5 days.
12.5.4.1.6 Neon Tetra Disease:
This condition is caused by an obligate intracellular parasite Pleistophora hyphessobryonis. It encysts in the back muscles of the neon tetra (Hyphessobrycon innesi) causing the dorsal bright blue stripe to become dull brown. Other tropical fish may also become infected. It is spread when the host dies and a new susceptible host ingests the affected muscle tissue. There is no treatment.
Monogenetic - these flukes do not require intermediate host. They are most commonly found in the aquarium fish.
12.5.4.2.1 Gyrodacytlus spp.
These flukes live on the skin and fins where they feed on epithelial cells and tissue fluids. Occasionally they are found infecting the gills. They are just barely visible to the naked eye. Clinical signs include discoloration of the skin, emaciation, and fraying of the fins. The small wounds produced by the parasite permit entry of bacterial and fungal invaders. Gyrodactylids lack visible eye spots. They are hermaphrodite and have one live young at a time which is capable of an immediate parasitization.
12.5.4.2.2 Dactylogyrus spp.
This is another common monogenetic trematode. It has four black eye spots at the anterior extremity. It is oviparous and the adults die after shedding large number of eggs. This fluke can destroy gill tissue and may cause respiratory distress if present in large numbers. The gill covers appear to be raised as the gill lamellae become distended. Affected areas of the gill are grayish white.
Treatment of many trematode infestations is by formalin baths (30 drops of 3% formaldehyde per gallon of water) for up to 30 minutes. This can be repeated in a few days if reinfestation should occur. Other agents which can be used include trichlorfon, copper sulfate, malachite green, methylene blue, potassium permanganate, and sodium chloride in dosages listed elsewhere.
12.5.4.2.3 Nematodes
Copepods (microscopic crustaceans) always serve as the first intermediate host for piscine roundworms. Care should be taken when wild caught copepods are used for food. Aquarium fish are often infected in outdoor production ponds. Camallanus spp. is the most common roundworm in aquarium fish. The parasites tend to protrude from the fish's vent. When startled they retrieve into the rectum. They are active blood feeder and can cause anemia.
Treatment with piperazine at a rate of 25 mg/10 grams of food has been reported. The tablets should be pulverized and mixed with a prepared gelatinous food mixture. It can be fed for a maximum of 10 days.
Fish can serve as either definitive host or intermediate hosts for tapeworms. The intermediate host stage in fish is called a Plerocercoid. These appear as cystic lesions which contain at least one scolex. They can occur in any organ. There is no treatment for the plerocercoid.
As a definitive host, the fish carry the adult tapeworm in their digestive tract. They can be treated with niclosamide (Yomesan) at a rate of 50 mg per 10 grams of food. A single treatment should suffice.
1. Argulus spp. [Crustacea; subgroup- Branchiura, "fish louse"]
It sucks body fluids through a sharp, stylet-like proboscis. A toxic substance is released from the proboscis glands which causes localized reddening and swelling. The death of young fish has been attributed to infestation by this parasite. The parasites are shield-shaped, flattened, and are 5 to 8 mm long.
If found few in number, they can be picked off with forceps. Trichlorfon baths at a concentration of 0.25 to 1.0 ppm may be used if the crustacean is in large numbers. The drug is rapidly hydrolyzed when placed in the warm water of an aquarium. It has no adverse effects (when used in therapeutic doses) on the beneficial bacterial flora in the biofilter. Treatment may be repeated once weekly for up to 3 weeks if necessary. Sources of trichlorfon include Dipterex, Dylox, Dryex, Chlorphos, Bot-x, Magoten, and Neguvan. Prevent exposure to children and pets.
2. Lerneae: [Crustacea; Subgroup- Copepoda, "anchor worm"]
Only the female is parasitic. They embed their "anchor" in the skin of gills and suck body fluids. Two egg sacs are attached to the posterior end of the female parasite. Damage is variable depending upon the number of anchor worms attached and their sites of attachment.
A 0.1% potassium-permanganate may be painted on the exposed parts of the lernaeid carefully avoiding contact with the fish's skin. The parasite may be removed with forceps once it dies. If the parasite numbers are high, the use of trichlorfon as described for Argulus spp. works well. Use 0.25 to 1.0 ppm of trichlorfon in the water once weekly for up to 3 successive weeks. Although this treatment kills the parasite, the head often remains embedded leaving an unsightly scar.
3. Ergasilus spp. [Crustacea; Subgroup- Copepoda]
It is a parasitic copepod which feeds mainly on the gill epithelial cells. The females are parasitic. The males are free-living and die shortly after copulation. They utilize extra cellular digestion and can severely damage the gill, causing severe hemorrhage. The heavily infested fish will show signs of respiratory distress, gasping at water surface and breathing rapidly. They may also scratch their opercle on aquarium objects. Microscopic examination of gill material will reveal the parasites with their clasper-like claw. Treatment is the same as for Arqulus spp. and Lerneae spp.
12.5.5.1 Anoxia or Gasping Syndrome:
This condition is easily recognized. The fish hang near the surface of the water, sometimes gulping air. The opercles will be flared and they will breathe rapidly. There are many possible causes of this syndrome.
Warm water will hold less oxygen than cold water. Deep tanks with small surface area limit air-water contact. Aeration will allerviate this problem by increasing circulation of "old" water to the surface to absorb oxygen and release carbon dioxide. Fish should not be crowded. The rule of thumb is one inch of fish per gallon of water in nonaerted tanks. This can be boosted to three inches in an aerated tank. This does not include the tail fin. Deep bodied fish have more mass per inch than thinner ones and therefore acquire more oxygen.
Rising ammonia levels will inhibit oxygen carrying capacity of blood. Decaying organic materials in the tank will use oxygen. Large numbers of plants with inadequate light will compete with fish for available oxygen. Additionally, damage to the gills through infectious or mechanical means, will decrease their oxygen extraction efficiency. Treatment requires correction of the inciting environmental problems.
12.5.5.2 Chlorine, Fluorine, Chloramine:
Chlorine and/or fluorine are dissolved in public water sources for health reasons. The use of chloramine instead of chlorine is increasing. This compound is more stable and breaks down into chlorine and ammonia.
These chemicals will cause gill damage and death of fish. They are effectively removed by commercially available water additives (usually sodium thiosulfate). Water for the new tank should be aged for 3 to 5 days with agitations. Use of the dechlorinating chemicals for small water changes (up to 10%) is safe. Chloramine breaks down into chlorine and ammonia. The chlorine leaves rapidly with aeration but the ammonia takes longer to dissipate. Test kits are available to analyze water for the presence, and level of these toxic substances.
12.5.5.3 Ammonia - New Tank Syndrome:
The main form of nitrogen waste excretion by fish is trimethyl-ammonium. It is rapidly broken down into ammonia. Ammonia is broken down in bacteria/nitrogen cycle to several compounds. The new tank lacks a high population of these beneficial bacteria (Nitrosomonas spp. and Nitrobacter spp.) and should be stocked lightly for 1-2 weeks to allow these to accumulate. The seed cultures of appropriate bacteria are commercially available. Alternatively, a cup of gravel from a healthy established tank will speed things up. The new tank will take at least 30 days to fully develop its biological filtration system.
When ammonia levels are low, the fish may "flash" against objects to itch themselves, dart around the tank, and hyperventilate. As levels rise and become more toxic the fish may have convulsions, become comatose, and die. A low pH will often be present. Ammonia is more toxic at high pH because there it exists in an un-ionized form (NH3) which can cross membranes more easily than the ionized form present at lower pH (NH4+). Ammonia test kits are available to help monitor tank conditions. Treatment requires a large water changes to reduce the ammonia concentrations.
12.5.5.4 Metals:
Dissolved metals such as copper, iron, chromium, or zinc will kill fish. Sources are copper pipping, water, and tank frame, or ornaments. Chelating solution for addition to water can be purchased at most aquarium supply shops.
12.5.5.5 pH Shock and Temperature Shock:
Most tropical fish can handle gradually changing environmental conditions such as pH and temperature. Sudden changes will kill or injure them.
A change of up to 0.2 pH units over an hour are usually well tolerated. Temperature changes of 1 to 3 degrees over a half to one hour are acceptable. Fish going from cooler to warmer tanks will have sluggish defense systems against bacterial and protozoa pathogens of the warmer tanks. It takes up to 14 days for the fish to fully adjust to a warmer environment.
The tank should have its pH and temperature carefully matched to the conditions of the incoming fishes' home tank. If this is not possible them floating the fish in a plastic bag full of its own water will provide a slow temperatures adjustment and exchanges of new tank water with that in the bag will allow a gradual exposure of the fish to its new home.
12.5.5.6 Congenital Defects:
A wide variety of defects including double headed, scoliosis, kyphosis, and anopthalmia have been reported. They may be congenital and/or hereditary. For more information, one of the listed references may be consulted.
12.5.5.7 Trauma:
This may be caused by rough handling or by aggressive tank mates. Wounds on fish provide an easy entry for theopportunistic microorganisms. If the environment is clean and the fish is healthy, the wounds will become covered by a small amount of bluish-gray slime and heal over a 5 to 10 day period. If they are easy to catch, merurochrome may be applied to the wound to prevent infection.
12.5.5.8 Aggression:
This is often a problem. Many species are extremely territorial and can be very physical in defense of their territory. Cichlids are especially notorious for this behavior. Fish raised together usually develop an armed truce. Big fish eat little fish. Rule of thumb is that a fish will eat whatever it can get into its mouth. One should study the species contemplated prior to acquiring them in order to better predict their community behavior.
12.5.5.9 Scurvy:
Fish do not synthesize vitamin C. Signs of deficiency are hemorrhage and slow clotting time in older fish; the skeletal deformity (scoliosis, kyphosis) will occur in growing fish. This is more of a problem with homemade foods than well-formulated commercial foods. Food cans should be kept properly closed and stored at cooler temperature to prevent the degradation of ascorbic acid.
12.5.5.10 Exopthalmos: [abnormal protrusion of eyeball]
"Popeye" can occur bilaterally or unilaterally. It is usually a sequela of asepticemic infection, or the result of a trematode encysting in the eye itself. It is not usually treatable and makes an unsightly specimen.
12.5.5.11 Neoplasia:
Tumors occur is fish occasionally. Some may be amenable to surgical excision. Others eventually will kill or incapacitate the fish. Those more commonly seen include papillomas and fibromas.
GENERAL REFERENCES
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- Brown, L. Anesthesia in fishes. J. Sm. Ani. Prac. 22: 385-390, 1981.
- Diseases of Fish, The Merck Veterinary Manual, Vith Edition, Published by Merck & Co., Inc., Rahway, NJ, 921-934, 1986.
- Dulin, M.Fish Diseases. TFH Publ. Inc., London, 1979.
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- Halver, J.E., Ed. Fish Nutrition. Academic Press, NY, 1972.
- Hawkins, A.D., Ed. Aquarium Systems. Academic Press, NY, 1981.
- Herwig, N. Handbook of Drugs and Chemicals Used in the Treatment of Fish Diseases. Charles C Thomas Publ., Springfield, IL, 1979.
- Newhaus, O. W. and Halver, J. E., Eds. Fish in Research. Academic Press, NY, 1969.
- Pseut, A. P. and Goldschmidt, M. Selected integumentary diseases of tropical freshwater fish. Comp. Cont. Ed. Vet. 5: 343-353, 1983.
- Ribelin, W. E. and Migaki, G., Eds. Pathology of Fishes. Univ. of Wisconsin Press, Madison, WI, 1975.
- Scott, P. W. Ornamental fish keeping and veterinary surgeon. J. Sm. Ani. Prac. 22: 331-343, 1981.
- Sommerville, P. Parasites of Ornamental fi