1.1. Learning objectives

• Gain an appreciation for the key organ systems in fish responsible for excretion, respiration and the control of osmolality
• Know the main physiological differences between saltwater and freshwater fish
• Gain a basic understanding of the importance of maintaining good water quality for aquarium fish and how this is achieved
• Be able to develop a basic clinical approach for a diseased fish presented for examination
• Gain an awareness of the environmental concerns affecting aquaculture and wild fish stocks

1.2. Suggested review for this section

• Please review the 1st Year Comparative Anatomy notes on fish prior to attending lecture
• Interactive anatomy and necropsy video at www.aquanic.org/real/necropsy/

2.1. Ornamental fish popularity continues to rise

• Zoo/Aquarium
• Pet
• Home aquarium and pond (sales over $500 million/year)
• Goldfish are statistically most popular pet
• 80% of fish owners own other pets

Commercial aquarium setting

2.2. Expectations of care similar to domestic species

• Owner will expect you as veterinarians to be able to help them when their fish are sick or die.

2.3. Fish as a food source becomes more and more important

• More and more veterinarians deal with fish diseases
• Food born diseases from fish meat (e.g. sushi) have zoonotic potential

2.4. Plentiful variety!

Leafy seadragon

• Scientific literature and medical knowledge increases at a fast pace
• > 20 000 species
• Smallest fish is 0.4 inches (10 mm)
• Largest fish (Whale fish) 45 feet (14 m)
• Anatomy and physiology varies with habitat of fish

3.1. Organs which are found in both fish and mammals but can have anatomical variation

As you go down the list, there are more anatomical differences

• Liver
• Spleen
• Stomach
• Intestines
• Brain / spinal cord

3.2. Organs found in mammals but not in fish

• Pancreas (Pancreatic tissue found in liver)
• Adrenal Glands-instead there is
  • Interrenal organ (cortical) anterior
  • Suprarenal organ (Medulla) near sympathetic ganglia
• Lymph nodes
• Bone marrow-Diffuse lymphomyeloid tissue in mesenteries, spleen, and head kidney
• Lungs
• Parathyroids

3.3. Organs which are found in mammals but are distinctly different in fish

• Kidneys (divided into head and tail kidney)
• Gonads-seasonally variable
• Skin-no stratum corneum
• Heart-two chambered

3.4. Organs which are present in fish but not in mammals

• Fins
• Lateral line
• Swimbladder
  • Physostomous-connected to the g.i. tract
  • Physoclistous-sealed off from the g.i. tract
• Gills-gas diffusion and waste dumping
• Ultimobranchial bodies-calcitonin production
• Pseudobranch-???-May have physiological connection with eye gas diffusion
• Corpuscle of Stannius (bony fish only)-electrolyte balance
• Pyloric appendages
• Spiral colon-elasmobranchs (sharks and rays)-increased surface area
• Rectal gland-elasmobranchs-electrolyte balance

3.5. Fins

• Dorsal fin :Stabilizer, Courtship, Defense
• Pectoral fin : counteract
• Pelvic fin : stabilizer
• Caudal fin : Motor
• Anal fin : Stabilizer, Gonopodium

3.6. Integument

• Bony scales of fish are overlapping plates of bone produced in the dermal layer.
• Epidermal cells cover the dermal plates. The outermost cells of the epidermal epithelium contain microridges of uncertain function.
• Analogue to terrestrial animal
• Epidermis consists of 6-8 layers of cells
• Glassfish: collagen is arranged in uniform pattern (cornea)
• Rapid metabolism
• Mucous (glycocalyx)
  • Full of antibiotic / antifungal enzymes and antibodies
  • Protective coating
  • Slough off pathogens
  • Can be detrimental in high amounts
• Alarm cells (pheromone)
  • Taste buds-some fish
  • to feed youngsters
  • to sleep (Parrotfish creates cocoon)
  • to protect from drying out (Lungfish)

3.7. Circulatory system

• Blood cells formed in liver, spleen, kidney
• Leukocytes may be normal at 10%
• Some fish lack hemoglobin (white blood)
• Lymph vessels but no lymph nodes
• Capillaries in gas bladder (exchange gas)
• Heat exchange in red muscles of lateral body wall (Tuna raises 4-6F)
• Heart
  • Position: Ventral to the gills
  • 4 chambers: Sinus venosus, Atrium, Ventricle, Bulbus arteriosus
  • The heart is a good place for phlebotomy

3.8. Urinary system

• Mesonephric kidney
• Organ of excretion and blood formation
• Head kidney is a lymphoid organ
• Several fish (swordtail) have urinary bladder
• NH₄ is excreted via gills

3.9. Gas bladder

• 1 or 2 chambered
• Caudal end connected to esophagus
• Primarily hydrostatic organ
• Vascular rete (gas gland) O₂ or N₂ in or out

3.10. Reproductive system

• Fish which school have little adaptations (spawn)
• Fishes in high-risk habitats evolved various mechanisms (mouth breeders, sex changes)
• The reproductive tracts of most teleosts are specialized for the production of large numbers of gametes that undergo fertilization and development in the external environment.
• Female teleost have ovaries with a central cavity which collects large numbers of ova before they are expelled via an oviduct to a genital pore. The ova lack the characteristic follicular development seen in mammals.
• Male teleosts have testes which may vary in size with the breeding period. The sperm are delivered from the seminiferous tubules to the external environment via a sperm duct which may join the most caudal end of the urinary (archinephric) duct in some species.

3.11. Musculature

• Most fibers are white - rapid contractions, short stamina
• Clinical relevance: White muscle disease due to Vit. E /Se deficiency

3.12. GI system

• GI tract is longer in herbivorous fish than carnivorous fish
• Digestion is temp dependant
• Mouth is limiting factor
• Barbels have tactile and gustatory function
• Fish lack a muscular tongue, but have one formed by the hyoid arch. Teeth and taste buds may be present throughout the oral cavity.
• Stomach is highly variable from no stomach to blind sac
• The stomach contains cells that produce both the secretions of chief and parietal cells found in mammals. Some fish lack a histologic stomach.
• Pancreas/gall bladder evident
• The intestinal ceca may be numerous and are located just after the stomach.
• The liver is large, tubular and has pancreatic tissue within it.

4.1. Breathing & Dealing with the External Environment

• O₂ is as important to fish as to terrestrial animals
• The Water environment
  • Oxygen poor, H₂O contains only 3% O₂
  • Osmotically unfriendly, H₂O is 800 times denser than air
  • A soup of pathogens

4.2. Osmoregulation

4.3. The Gill

4.3.1. Gill Physiology

• Respiration
• Hemoglobin varies in fish species
  • Goldfish-high affinity for oxygen
  • Trout-quick release of oxygen.
  • Some fish lack hemoglobin (White blood)
• Efficiency
  • Under ideal conditions 80 % of O₂ is removed(Humans use 25 % of inhaled O₂)
  • This efficiency will also harm the fish (supersaturating- gas bubble disease)
  • Can accumulate concentration of toxic material of 100 (to 1 million) times higher than concentration found in water
• Surface of gill is 6-10 times greater than surface of fish
  • Lung surface is 100 times greater
• Important second function as excretory organ - loss of ions and water
• Problems with abnormal water quality: Decreased pH and increased CO₂ cause quick release of oxygen-Bohr effect.

  Bohr effect: Hb not only furnishes oxygen to tissues, but also transports the waste products of metabolism from the tissues. So there must be some regulatory interplay between these two functions, and the mechanism of this regulation of Hb is called the Bohr effect. At the tissues there is high [carbon dioxide] and [H⁺] i.e. low pH, and this lowers the Hb affinity for oxygen

• H₂O must constantly been drawn over the gills (but: Fish do sleep!)

  Mostly water is drawn in per the mouth

  • Sharks have slits on first gill branch
  • Tuna, trout etc. just keep mouth open when swimming (1 mph)
• Excretion of ammonia
  • Passive and active transport.
  • Mostly concentration gradient dependent high environmental ammonia = prevents ammonia from being excreted out the fish = toxic
  • Energy required, even if fish is dormant
• Acid base balance: Enzyme function, molecular function.
• Monovalent exchange: Osmotic balance and enzyme efficiency (kidneys excrete divalent cations)

(Images adapted from Aquariology Fish Anatomy Physiology and Nutrition by Gratzek, John Gratzek, Howard Evans)

All these functions are necessary for homeostasis!!!

For more visit illustrationshttp://www.fishdoc.co.uk/water/open_systems.htm

4.4. Skin Pathology

• Break in the skin barrier
• Breech in osmotic barrier-stress
• Breech in pathogen defense-mucous tries to compensate

4.5. Kidney

Osmotic Balance: Saltwater verses Freshwater

• Immune response
• Blood production
• Excretion of cations (Ca⁺⁺, Mg⁺⁺, excess water, etc.)

Freshwater fish are hypertonic in comparison to their environment. They have to eliminate water constantly from their body. In fish with kidney disease, ascites is very common, as the elimination of water from the body is impaired ("Pine cone" look).

Fish in the marine environment are hypotonic and lose water at a high rate. They have to drink seawater and excrete the minerals mostly via the gills.

4.6. Other important physiological organs

• Rectal gland in sharks and rays - Elimation of excess Na
• Olfactory organ - Homing process in salmonids
• Lateral line organ - Mechanoreceptors
• Ear

5.1. Basic Water Quality Parameters

• Salinity
• Temperature
• Dissolved oxygen
• Ammonia
• Nitrite
• pH and hardness
• Other parameters

5.2. Types of Filtration

• Water changes
• Mechanical
• Biological
• Chemical
  • Carbon
  • Ion Exchange

5.3. Disinfection

• UV light
• Ozone

5.4. Water Quality Monitoring Equipment

Test kits run from $ 20 to $ 2000. The accuracy of the result is reflected in the price of the test. (See list of test kit manufacturers at end of chapter)

• Refractometer
• Thermometer
• Colorimetric tests
  • Ammonia
  • Chlorine
  • Dissolved oxygen
  • Nitrite
  • PH
  • Alkalinity/hardness

6.1. Definition of disease

A pathological entity characterized usually by at least by two of these criteria: a recognized etiologic agent(s), and identifiable group of signs or symptoms, or consistent anatomical alterations.

6.2. Disease continuum

Because of all the factors involved, fish diseases can be very confusing and frustrating. Also some diseases manifest in fish with very different signs (e.g. mycobacterium marinum) and lots of diseases manifest with the same clinical sign (e.g. cataract). Therefore, identification of the causative agent(s) and the nature of the predisposing condition(s) are both important in disease control and long-term prevention.

Consider the physical properties of water as the primary environment of fish:

• Fish are much more closely connected with their immediate environment than terrestrial animals (water vs. air)
• Water transports all kind of pathogens much more efficiently than air
• Water will keep pathogens alive better than air (drying is one form of sterilization)

6.3. Stress

Stress is the sum of the biological reactions to any adverse stimulus, physical, internal or external, that tends to disturb the homeostasis of an organism. Should these reactions be inappropriate, they may lead to disease states. The term is also used to the stimuli that elicit the reaction e.g. heat, nutrition, confinement, transport etc.

7.1. Environmental

All the chemistries are closely related to each other. A certain concentration of ammonia or nitrate may be tolerable at the optimum temperature but toxic at 5 10 degrees higher. Remember fish are poikilotherms!!!!! The immune system and all physiological processes need the species-specific optimal temperature to work best.

KNOW THE AMMONIA CYCLE!see below

• New Tank Syndrome
  • Ammonia
  • Nitrite toxicity
• Supersaturation-Gas Bubble Disease
• Chlorine toxicity
• Low dissolved oxygen

7.2. Other common mistakes and pitfalls encountered in the aquatic patient:

• Failure to know your animal
• Failure to allow a system to age and come into balance before adding organisms.
• Overcrowding, which taxes the oxygen supply and the waste processing capacity of the system and increases traumatic injury, territorialism, and cannibalism.
• Overfeeding
• Failure to rinse recently disinfected vessels and implements
• Failure to quarantine newly arrived stocks or to isolate animals undergoing treatment.
• Failure to rinse dust from activated carbon, dolomite, or crushed shell when recharging a system.
• Clogged seawater lines due to accumulation of fouling organisms and resulting in decreases in water flow rates.
• Failure to remove dead animals or decaying food.
• Use of plastics impregnated with insecticides and fungicides (certain bathroom sealers).
• Use of toxins or solvents in or around aquaria (floor stripping, pest control).
• Failure to separate certain species (placing the predator with its prey or the parasite with its host).
• Failure to check the pH and specific gravity of culture solutions.
• Inadequate nutrition due to underfeeding or an unbalanced diet.
• Failure to keep adequate records of water quality data or other significant events and failure to review the data
• Failure in anticipating the onset or duration of reproductive activity or in misinterpreting reproductive behavior as aberrant
• Use of brass, bronze, or copper valves or piping which can corrode and slough off or leach toxic copper salts. Copper is especially injurious to invertebrates.
• Failure to provide proper substrates, shelter, or support of commensal organisms.
• Improperly secured electrical equipment, frayed wires or outlets not protected by ground fault interruption.
• Failure to observe all pipes, fittings, and equipment on the suction side of pumps for air leaks. Supersaturated water can kill.
• The belief that antibiotics will solve all your problems.

7.3. The ammonia cycle:

A very common mistake done by the novice aquarist, is setting up the system and not allowing time enough for the ammonia cycle to go through all its phases until it is safe for fish and invertebrates. This common mistake is often referred to as new tank syndrome. As the system is set up and plants and one or two fish are introduced, an initial built-up of ammonia will occur due to fish excrements, dead plant material and food leftovers. Slowly a bacterial population (nitrosomas sp.) will build up and transform the ammonia into nitrites which are slightly less toxic than ammonia. A second population of bacteria (nitrobacter sp.) will change the nitrites into nitrates, which are not very harmful to the fish.

The ammonia/nitrogen cycle

8.1. Parasites

Get live fish for diagnostics! External parasites will leave or die when the host dies.

Avoid having invertebrates (esp. snails) in tank as they are intermediate hosts for lots of parasites!

8.1.1. External parasites

8.1.1.1. Protozoa

• Ich (Ichthyophthirius multifiliis): Skin scrape, gill clip, see ciliate on cytology
• Treatment for Ich: Malachite green at 0.1 mg/l q3d x 3
• Trichodina spp.: Skin scrape, gill clip
• R/O fungal diseases

8.1.1.2. Crustaceans

Lernaea spp.(Anchor worm): Skin and gill exam Argulus spp.(Fish lice): Skin exam Only a little knob Animals are irritated (show flashing, scraping) Treatment Potassium Permanganate (traditional, very caustic) OR Lufenuron (Program, Anchor Away) can be used (chitin inhibitor) at 1 tab (490 mg) per 1000 US gal. (0.1-0.2 mg/L) The veterinarian should be aware of a possible risk to native aquatic arthropods from waste water runoff

8.1.1.3. Trematodes

• Skin and gill exam
• Gyrodactylus-live bearer
• Dactylogyrus-egg bearer
• Digenetic trematodes

8.1.1.4. Leaches

• Skin examination

8.2. Bacterial Diseases

Remember that fish live in a bacterial soup and are constantly challenged by their presence. A lot of infections are opportunistic.

• Common sign is hemorrhages in fins and scales
• Fin rot
  • Fin rot is a bacterial disease involving opportunistic bacteria such as Aeromonas, Pseudomonas or Flexibacter that abound in all aquatic environments + Stress
  • It is usually self-resolving as they settle in, but does demonstrate just how sensitive fish can be to stress and how fin erosion is often a sign that all is not well.
  • Investigation into a underlying cause should continue!!

  Injected vessels in the tail fin

  Finrot

• Mycobacteria
  • Improperly called Fish T.B.
  • Probably the most frequent disease
  • All species are susceptible
  • Found in the water
  • Squash of liver, spleen-acid-fast stain
  • Culture will take 1 month - make sure the lab knows the sample is from a fish, so that they culture under the right conditions and look for fish mycobacteria
  • Zoonotic potential
  • Always wear gloves when handling fish or cleaning an aquarium
  • Treatment difficult, culling and disinfection, Kanamycin might be best

• Aeromonas hydrophila: Culture of blood, liver, kidney; zoonotic
• Vibrio spp: Culture of blood, liver, kidney; zoonotic
• Edwardsiella tarda: Culture of deep ulcers, blood
• Columnaris: Squash prep of gills
• Anaerobes

8.3. Viral

• Infectious salmon anemia (see article on APHIS site)
• Lymphocystis: Squash prep and histopathology
• Viral Hemorrhagic Septicemia - Viral isolation

• Once diagnosed in pet fish, concentrate on immune modulators (Vit.C, levamisole, best aquarium conditions)

8.4. Fungal

Usually true opportunistic invaders. Also check for underlying stressor.

• Saprolegnia
  • can act as a primary pathogen infecting fish that havent shown signs of previous damage
  • It is believed that such attacks are temperature-dependant, usually occurring at low temperatures, possibly as a consequence of a reduced immune response
  • Diagnose with skin scrape and gill clip (looks like cotton wool)
  • R/O Ich

Identification of the causative agent and the nature of the predisposing condition are both important in disease control and long-term prevention.

Saprolegnia infection in a fish

9.1. Different settings

• Pond vs. Aquarium
• Individual (small animal medicine) vs. Herd health
• Big differences, but same physiology, same environment

9.2. History

• How long have you been keeping fish?
• What are the problems with the fish today?
• When did you first notice these problems?
• How long have you owned the sick fish and where were they obtained/purchased?
• Are there other fish in the same tank or pond with the sick fish, and if So, how are they?
• What is the size (volume) of the pond and how is it heated, filtered, and aerated?
• Do you have a water test kit, and if so, how often do you test the water?
• What are your most current results?
• What and how often do you feed your fish?
• Have the fish already been treated? If so, by whom and with what medications?
• Is there a possibility that the fish were exposed to some type of toxin?

9.3. Aquatic Environment

• Fish are ectothermic
  • Pond vs. Aquarium
  • Every reaction is governed by temperature of system
• Improving the water quality and environmental conditions are key to success
• Most diseases are related to disturbance of the balance between waste production by the fish and its metabolism by the bacteria in the biological filter.

9.4. Feeding

9.5. The different disease patterns

• Sudden onset + all species affected = Environmental Problem
• Gradual onset + increasing no. affected = Infectious Disease
• Isolated cases + small no. affected = Non- infectious Disease

The bacterial soup - Parasites are always present on fish in controlled number

Stress often results in an increase in pathogens and results in disease

9.6. Approach to the caseCrisis management

A step by step procedure:

• Perform water testing
• Isolate the fish and keep in Quarantine (Koi may need a buddy)
• Change water
  • Change 1/3 of tank/pond water to dilute poor conditions
• Reduce feeding
  • It will add extra ammonia to the system
  • It will also improve acceptability of medicated foods
• Make sure aeration is proper
• Add un-iodized salt@ 2 g/l (1/4 ounce/gal) = 0.2 % solution (2 ppt)
• Check Filter
• Reduce Stock density

9.7. The physical exam

Generally the clinical signs are very non-specific and sometimes not uniform!!

• Exophthalmus
• Cataract
• Dropsy
• Strange breeds vs. tumor
• Trauma/Furuncle

Emaciation and Dropsy in Zebra Danio

Pinecone appearance from several angles

9.8. Diagnostics

9.8.3. Direct microscopic examination at 10X, 20 X and 40X

• New Methylene blue stain, Gram stain
  • Gill biopsy
  • Mucous smear
  • Fin biopsy

9.8.4. Hematology and Blood Chemistry

• Phlebotomy

9.9. Treatments

Depending on the severity and circumstances of the situation (pet fish in one aquarium vs. 1000 of fish in commercial aquarium or pet store) different forms of delivering the medication might be chosen. Apart from the direct medication by injection or topical application there are different indirect ways to medicate the fish. See next section for specifics on pharmaceuticals.

9.9.6. Injections

• Intramuscular in longissimus dorsi
• Intracoelomically

IM Injection

9.9.7. Some problems with treating fish

• The Pathogen
  • Not all ectoparasites are easily eliminated with one dose (e.g. white spot requires repeated treatments)
  • Drugs can be difficult to obtain (e.g. lice and anchor worm usually require organophosphates)
  • Not all bacteria can be treated easily (e.g. Mycobacteria are found deep inside lesions.)
• Drug Resistance - Bacterial resistance to antibiotics is now an important factor in the treatment of bacteria diseases of fish. Culture and sensitivity tests may take too long to complete but it is often essential to start treatment as soon as possible to avoid a disease "explosion"
• In-contacts - many fish pathogens are infectious or potentially infectious, therefore all in-contact fish should be treated enmasse.
• The Patient
  • Small fish and fry may be too small to inject safely.
  • Severe illness - too ill (e.g. gill disease) to inject or handle without causing serious stress.
  • Unpalatable drugs (e.g. some antibiotics) and anorexic fish limit the use of in-feed medications.
  • Shoaling - Some fish prefer company particularly in isolation facilities, even if it is with other species.

9.10. Nutritional support

• For the most part, captive fish are overfed and fed an inappropriate diet
• Increase to allow for increased metabolism
• Oral intubation-no worry about aspiration but water fowling and coating gills are problems. Some animals will regurgitate when tubed under anesthesia. Make sure you have fresh water around to flush over gills if they are covered with food material.

9.11. Anesthesia

• Tricaine Methane-sulfonate (MS-222) Carcinogenic!!
• Clove oil (Eugenol) (Mix 1:10 with 95 % ethanol for stock solution) 25 50 mg/l will anesthetize fish. Recovery period is longer than with MS-222.
• Isoflurane-special ventilation to decrease human exposure.
• Make sure recovery water is available (temperature and pH matched)

Preparation for surgery

Induction

9.12. Surgery

• Anesthesia set-up
• Absorbable monofilament. Remove suture after 3 weeks !!
• Standard surgical technique.

	Surgery in a goldfish
	Ophthalmic surgery for exophthalmos in a fish

9.13. Imaging

• Radiology
  • Can be done awake or under anesthesia
  • Fish will struggle initially but then remain calm
  • To protect the fish at all times is utmost importance
• Ultrasound
  • Water is best medium for utlrasound exam

10.1. Antibacterial

• Oxytetracycline
• Ciprofloxacin
• Enrofloxacin
• Amikacin
• Trimethoprim-sulfas
• Watch salt water and antibiotic baths-salts (Ca⁺⁺, Mg⁺⁺ may bind such antibiotics such as tetracycline rendering the antibiotic functionless)

10.2. Antiprotozoal