Aquatic species
Last updated on September 12, 2010
Fish diseases
General information
Biology
Cephalopods
(squid, cuttlefish)
Common laboratory fish species{3982}
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Common name
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Latin name
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Uses
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Common carp
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Cyprinus carpio
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Aquaculture
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Channel catfish
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Ictalurus punctatus
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"
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Tilapia
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Tilapia spp., Oreochromis spp.
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"
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Atlantic and other salmon
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Salmo salar, Oncorhynchus spp.
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Comparative physiology
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 Rainbow trout
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Oncorhynchus mykiss
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Comparative physiology
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Platyfish
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Xiphophorus maculatus
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Carcinogenesis
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Swordtail
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Xiphophorus helleri
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Carcinogenesis
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Fathead minnow
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Pimephales promelas
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Carcinogenesis, toxicology
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Zebrafish
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Danio rerio
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Developmental
biology, carcinogenesis
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Medaka
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Oryzias latipes
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Developmental biology, carcinogenesis
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Killifish
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Fundulus heteroclitus
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Endocrinology,
development
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Goldfish
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Carassius auratus
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Neuroscience,
nephrotoxicology
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Electric eel
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Electrophorus electricus
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Neuroscience,
nephrotoxicology
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Electric ray
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Torpedo californica
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Neuroscience,
nephrotoxicology
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Top
Fish have several physiologic features that make
interesting experiments possible.
 | Melanoma occurs in platyfish-swordtail hybrids, and serves
as a model of genetic factors in carcinogenesis.. Neither platyfish (X.
maculatus) nor swordtails (X. helleri) develop melanoma. F1
hybrids with the spotting trait may develop pre-melanomas. F1 x swordtail
produces frank melanoma.{3571} |
|
Electric ray axons are studied
in neurobiology |
| Vertebrate developmental genetics are studied in zebrafish
and medaka, which can be made using transgenic technology. {3982} |
Transgenic fish are useful compared to mammals, because the egg is
fertilized externally, the embryos are usually transparent, and the
investigator can manipulate both ploidy and the gender of the fish. Genes that
have been manipulated include those for growth hormone, insulin-like growth
factor, and antifreeze proteins. Lysozymes or viral antisense RNA genes are
used to immunize commercially valuable fish against pathogens. There is great
concern over potential accidental release back into the wild with some of these
fish.{3982}
Integument{3571}
| No keratin layer as in mammals; covered by a cuticle comprised of mucopolysaccharides,
mucus, sloughed cells, immunoglobulins, and free fatty acids
|
| Scales are calcified plates covered with epidermis, and originate in the
dermis. Elasmobranch fish (sharks and rays) have ctenoid scales with
spicules, while teleost fish (bony fish) have cycloid scales having a smooth
outer surface and concentric rings making them useful for age determination. |
| Pigment-containing cells of the dermis contain melanin, guanine, or
exogenous carotenoids which may be self-modified to change color intensity
and quality. |
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Respiratory system{3571}
| Fish expend much more energy during respiration than mammals, due to low
oxygen tension and high weight of the water |
| For each 10°C rise in water temperature, oxygen demand increases by a
factor of 2-2.3 |
| Sea water carries 20-23% less oxygen than fresh water |
| Because of these limitations, fish are excellent sprinters, with large
amounts of white muscle fibers in which there is rapid build-up of lactic
acid that takes hours to metabolize. |
| When confronted with reduced oxygen content, fish respond differently:
 | teleosts increase respiratory flow rate |
| elasmobranchs maintain or reduce respiratory flow rate |
| both increase blood pressure and decrease heart rate, enabling the
heart muscle to absorb oxygen from venous blood |
| Under chronic hypoxic conditions, some species can acclimate to lower
oxygen levels |
|
| CO2 influences the blood's affinity for oxygen
| Bohr shift: hemoglobin has less affinity for oxygen when CO2
increases or pH decreases. Oxygen is therefore more easily released at
metabolically active sites, and more easily taken up at the gills where
CO2 dissipates in the water. |
| Root effect (only in teleosts): hemoglobin loading of oxygen depends
on pH. At high pH in the gills, oxygenation= 4x deoxygenation. At lower
pH in the tissues, deoxygenation = 400x oxygenation. |
|
| Gills are the primary site of air exchange, but some can take place in the
skin (benefits only the skin). Some fish have accessory breathing organs
(sacs in the oral cavity, modified gills, and lungs or modified swim
bladders) that allow them to use air as well as water (i.e. the Betta and
other tropical fish) |
| Gills utilize countercurrent mechanisms with blood flow counter to water
flow. This allows fish to remove 40-80% of the available oxygen from the
water. |
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Circulatory system{3571}
| The heart consists of a ventricle, bulbus arteriosis, atrium, and sinus
venosis. Some authors consider the bulbus arteriosis or the sinus venosis as
a "third chamber." |
| Blood flow goes from the ventricle--bulbus arteriosis (maintains blood
pressure)-- ventral aorta--afferent branchial arteries--gill arches--gills--
efferent gill arteries--dorsal aorta--viscera and muscle--heart |
| Note that the heart receives only venous (unoxygenated) blood |
| Some blood from the dorsal aorta enters modified first gill arch (pseudobranch)
and traverses a countercurrent capillary bed. It then enters a second
countercurrent system in the choroid gland posterioventral to eye; this
supplies oxygenated blood to the retina, which in the fish is the most
highly oxygen-demanding tissue. |
| In small fish, blood is sampled by cutting off the caudal peduncle (mixed
venous and arterial blood). In large
fish, heart puncture is used (pure venous blood).
|
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Urinary system{3571}
| Fish kidneys are much more primitive than mammalian kidneys (but see
below). |
| Kidney is the major site of
hematopoiesis in the fish
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| May be divided into "head" and "trunk" kidneys
depending on species |
| Freshwater fish must conserve ions and excrete water, while saltwater fish
must do the opposite. |
| The majority of nitrogenous wastes are removed through the gills. |
| Chloride cells of the gills, operculum and buccal cavity are the major
site of osmoregulation. |
| Several species can regenerate entirely new nephrons following
toxic insult; this phenomenon is unique to fish. It has been shown to occur
in goldfish, trout, tilapia and toadfish (although the Army quotes a ILAR
journal saying that toadfish have no glomeruli and therefore are not
susceptible to gentamicin toxicity). This has been studied in goldfish, in
which it was found that they regenerate nephrons after repeated injections
of gentamicin at 50mg/kg. This may be a valuable biomarker of environmental
nephrotoxicosis.{4599} |
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Reticuloendothelial system{3571}
| Fish have no lymph nodes or functional hepatic Kupffer cells. |
| Fish have phagocytic cells in the endothelial lining of the atrium and the
gill lamellae. |
| Melanomacrophage centers are found in the spleen, kidney and liver, and
have also been observed in amphibians and reptiles. Melanin inhibits free
radicals and has a bactericidal action via hydrogen peroxide production.
This is not a temperature-dependent system, which is important in
poikilotherms. |
| Teleosts are immunocompetent: they produce immunoglobulins (only IgM),
have cell-mediated immunity (the thymus may produce B cells early, but later
only T cells), both delayed and immediate hypersensitivity, and immunologic
memory. |
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Digestive system{3571}
| Fish can be carnivorous, herbivorous (carp), or omnivorous; the length of
the GI tract varies accordingly. |
| Fish have teeth in the pharynx as well as the oral cavity. |
| Taste buds may be found on the skin as well as the oral cavity, pharynx
and esophagus. |
| Liver is more primitive, and not lobulated, but it does metabolize toxins
via similar enzyme systems. |
| The swim bladder or air bladder is found in many fish. It is an
outpouching of the GI tract. It adjusts specific gravity, reducing the
amount of energy expended to keep the fish at constant depth. In fish living
at great depths it may be filled with oil. In some air-breathing species,
the swim bladder acts as a modified lung. |
| Some fish (salmonids, ictalurids and others) have an absolute requirement
for vitamin C, while others (carp) can synthesize it. |
| In general, salmonids and most other fish require very high protein, and
produce most of their glucose from amino acids. Carbohydrates in the diet
are therefore not useful for energy production, and fish store it readily as
glycogen but release it very slowly. |
| Provision of proper diet can be difficult due to the lack of knowledge of
specialized needs; for example, the jawfish will develop thyroid hyperplasia
on a diet containing adequate iodine for most species{3571} |
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Endocrine system{3571}
| No parathyroid or other hypercalcemic organ in the fish. |
| Calcitonin produced by the ultimobranchial body near the esophagus.
Corpuscles of Stannius in the kidney also decrease calcium. |
| Corticosteroids are produced by the inter-renal tissues of the head
kidney. They also act as mineralocorticoids. |
| Pineal gland produces melatonin in the absence of light. Melatonin
influences melanin distribution in the skin and circadian activity. |
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Acousticolateralis system{3571}
| Teleosts are the most primitive vertebrates able to detect sound |
| Fish have ears and lateral line organs |
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Reproduction
| The electric eel and the Amazon molly (Poecilia formosa) are all
female, and all identical. In the molly, sperm of closely-related species
stimulate the development of the ova but do not contribute to the genetic
makeup of the offspring.{3571} |
| Chromosome sets can be manipulated by
temperature shock, change in pressure or chemically to induce triploidy or
tetraploidy. |
| Radiation of gametes inactivates them, so the resultant offspring
will have only the genetic material from one parent. In one study using carp
(Cyprinus carpio),
the statistical power of the results using isogenic fish was significant,
compared to using standard diploid fish.{3534} |
|
Sex-reversal can be
induced with hormone treatment. |
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Fathead minnows (Pimephales promelas) are common fish native to North
America. The larvae are used to monitor the toxicologic effects of effluent
discharges. A substantial body of toxicology data exists for this species. An
online digital atlas (http://som1.ab.umd.edu/AquaticPath/fhm)
of the histology of the fathead minnow has been produced by scientists at the
University of Maryland.{4516}
Zebra fish (Danio rerio) are popular omnivorous warm-water laboratory
fish, but there is much to be learned about an optimal diet. One study
determined that a high ratio of n-3 to n-6 polyunsaturated fatty acids produced
better growth and reported historically higher fertility when such diets were
fed. Fish require both linoleic and linolenic acid in their diet.{4187}
In a CT "Diagnostic Exercise", zebrafish obtained from the local
pet store were kept in 1-gallon tanks with 20 fish per tank. The filtration
system consisted of mechanical, UV and biological filters with a pump flow rate
of 8 gallons/minute serving a total of 220 tanks. Source water was
reverse-osmosis purified with sea salt added. Two weeks prior to stocking, a
commercial source of bacteria (Nitrosomonas and Nitrobacter) was
added to the water to populate the biological filters. Approximately 4 weeks
after arrival, many fish developed petechial hemorrhages and ulcers on the skin
on several areas of the body. Some were observed to swim at odd angles.
Histologically, the epidermis had multiple ulcerations and mononuclear cell
infiltrates, with multifocal necrogranulomatous myositis in skeletal muscles.
Aggregates of Gram positive bacteria were seen under the skin surface and on the
spinal cord. Cultures were negative for fungi. Skin bacteria isolated were Aeromonas
caviae and A. sobria externally. The interior skin swabs yielded A.
caviae, Plesiomonas shigelloides, beta-hemolytic and gamma Strep.
Water testing showed that nitrite levels were 1-5ppm, ammonia 0, pH 6.8. The
conclusion was that the fish were stressed by high nitrite levels, because of
insufficient time to allow the nitrogen cycle to develop. Aeromonas is
part of normal skin flora but can cause lesions in stressed fish. The fish were
also overcrowded (1 inch of fish per gallon of water is the rule of
thumb).
The
diagnosis was therefore "motile aeromonad septicemia", aka ulcer
disease, aka aeromoniasis. The problem resolved with tincture of time and
decreased stocking density. The Plesiomonas and Strep, along with Xanthomonas,
Flaviomonas and Bacillus cultured from the water, were relegated to
the department of raised eyebrows.{4188}
Toxicology studies in Danio
Early life stages of fish are more sensitive to chemical stress than juvenile
and adult stages. This is due to their large body surface, undifferentiated
epithelia, and the vulnerability of the developmental process itself. Zebrafish
(which are in the family Cyprinidae) are related to the most abundant cyprinid
fish in Europe such as roach (Rutilus rutilus) and bream (Abramis
brama). They have translucent, non-sticky eggs making them easier to handle
than Northern Hemisphere fish. To date, the fathead minnow (Pimephales
promelas) and the African clawed frog (Xenopus laevis) have been used
more for toxicology, but now there is a short-term zebrafish embryo assay which
has potential to become a standard.{4517}
A simple and efficient housing method involves maintaining breeding groups
(12 wild-type females and 15 males) in glass aquaria (100L capacity). Such
groups produce approximately 1000 eggs per day with 80% viable. The sides of the
tanks are covered with dark cardboard, which encourages less dense schooling and
more pronounced coloration. Light is maintained at 14:10. Water is either Berlin
tap water or RO water with 200mg CaCl- x 2 H20, 103mg NaHCO3,
and 100mg sea salt per liter. Conductivity is 800µS/cm at pH8. Water
temperature is 26°C, supplemented with heaters if necessary to encourage egg
production and keep the fish robust. Biofilters must have adequate surface area.
Clumps of fern are added to provide shelter for spawning, and snails (Melanoides)
to keep the glass clean. Fish are fed 3x per day with either frozen white worms
(Chaoborus), daphnia, or adult brine shrimp (Artemia). Dry flake
food is used on weekends in feeders.{4517}
Fish spawn at the onset of light on the day after a clump of fern is added
covering a spawning box in the tank. Eggs are removed and rinsed with artificial
water (ISO 7346/3) and placed in Petri dishes. Incubation media is changed
daily. Plates are kept semi-statically at 26C and 12:12 light:dark. When
examining embryos at various set points in development, one must be fast or else
the other embryos will be at a different stage when examined.{4517}
Stages of development at which measurements can be made include:
| (1) 4hr is the late high blastula stage; |
| (2) 8hr is late epiboly (late gastrula, embryo still spherical); |
| (3) 24hr is prim-6 (basic body organization, beginning of heart beat,
melanophores in the eye, spontaneous movements); |
| (4) 32hr is prim-16 (blood circulates, melanophores on trunk); |
| (5) 55hr is pec-fin (hatching begins, melanophores pronounced, blood
circulatory system fully developed); |
| (6) 80 hr is protruding mouth (eleutheroembryo resting on side, still yolk
present, xantophores present making embryos yellow); |
| (7) 144 hr is early larva
(body orientation upright, swim bladder
inflated, swimming and feeding). The short-term embryo test can be extended
to 21 days, when fish are weighed and measured.{4517} |
The first toxic effects of a test compound can be seen during blastogenesis;
in the worst case, development stops before epiboly. Malfunction of epiboly
inhibits formation of the anterior-posterior body axis, or causes protrusion of
the yolk, exogastrulation, or retardation of organogenesis. Advanced embryonic
lesions may include edema around the heart and yolk, bent tails, lordosis,
pectoral edema and blistering, or tail necrosis.{4517}
Advantages of performing a semi-static test are (1) low demand for test
chemicals; (2) easy access to the developing embryos in the dish, and (3)
endpoints that are simple visual measurements. Limitations include (1) it is
short-term only, vs. life-cycle tests or fertility studies; (2) sample quality
changes with time in the dish, due to microbial action and metabolic by-product
buildup; and (3) lipophilic compounds that can't be added to the water must be
injected in the yolk.{4517}
Advantages of using zebrafish over other aquatic systems include (1)
artificial hormonal control of reproduction is not necessary (vs. Xenopus);
(2) non-sticky translucent eggs are easy to see.{4517}
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 The two
most common laboratory cephalopods are the cuttlefish (Sepia officinalis)
and Pacific long-finned squid (Sepioteuthis lessoniana). Several
generations have been raised at the National Resource Center for Cephalopods of
the Marine Biomedical Institute in Galveston, Texas. These animals live
approximately one year in a semelparous lifestyle (grow rapidly to sexual
maturity, spawn once, and die). Squid live in the water column (pelagic) that
must be at least 1 meter deep, whereas cuttlefish are bottom-dwellers (benthic).
They grow rapidly in the juvenile stages and require virtually pure protein
diets to achieve this. Shrimp, crab and non-oily fish can be fed. They produce
highly nitrogenous waste, about 2-3 times the amount of ammonia per kg as fish.
They have superb (although black-and-white) vision to enable them to compete for
prey. They are also able to use camouflage.
High water quality through filtration is especially important for rearing
these animals. The NRCC system utilizes a foam fractionator (protein skimmer),
mechanical 100µm filter, activated carbon, and a biologic filter with crushed
oyster shell, finished by a UV sterilizer. The entire volume is filtered every 2
hours. Cephalopods are sensitive to rapid changes in pH, salinity, low-dissolved
oxygen concentration and nitrogenous waste. Maintaining low nitrogen levels is
important to proper management. The tanks must have tops, because both species
can jet themselves right out in response to sudden motion or light changes.{3787}
| Copper treatment, used for many invertebrate diseases, is highly toxic to
cephalopods. |
| Stress is associated with inking in the water. |
| Crowding can result in aggressive behavior. Frequent observation of animal
behavior is the single most important management strategy in a quality
animal health program. |
| Animals can be injected IM at the base of the arms until they are well
enough to be able to consume drugs in their food. |
| Euthanasia can be achieved by rapid cooling in iced sea water or
administration of a 10% solution of ethanol in sea water. Necropsy should be
performed immediately because of the rapid autolysis of these animals. |
| The immune system is rudimentary. Cephalopods have only one type of
circulating hemocyte that clumps and isolates but does not phagocytize
foreign materials. The humoral immunity consists of a hemagglutinin protein
that may function similarly to lectins in other invertebrates.{3787} |
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