Fish Medicine

Question 1

‘Pet’ fish temperate freshwater - Goldfish basic requirements (Teleosts)

Answer 1

• 30 L water per fish
• 1 ft^2 of air surface per fish, can be reduced by aeration (pump pushing air through water, will inc SA + reduce air at tank to maintain oxygenation)
• Maintain 18 - 20 C, warmish room temp
• Cope in open-air pond year-round
• Ponds preferable to tanks if deep enough to avoid freezing/shade available in summer
• Feed on crustaceans + plants or pelleted food (flakes)

Question 2

Koi karp

Answer 2

• Large ponds 1.5 m depth
• Filter w/ biological + physical filtration to accommodate their size + metabolism
• Multiple chambers in filter - filter out lumps of organic material -> sand type, takes out smaller particles -> biological filter - may be spoken w/ bacteria that break down protein by-products in water + remove, water flows back = relatively clean
• Aeration - waterfalls for larger systems
• Commercial diets - vit C, carotenoids to maintain bright colouration

Question 3

Common issues of carp

Answer 3

• Water quality failings, problems w/ protein breakdowns - inc NH3, nitrates or nitrites - should be removed by water changes/used by aquatic plants
• Any organic material in water produces NH3 + NH4+
• NH3 more toxic - causes damage to surface of fish + diffuses across gills
• Need idea of proportion of NH3 : NH4+
• Mod levels but have alkaline pH/high temps, get shift of NH4+ -> NH3, will higher NH3 than results suggest
• NH3/NH4+ oxidised by bacteria mostly in filtration system -> NO2- (nitrite) -> oxidised further to nitrate (NO3^2-), dec toxicity, tend to be sequestered in water + doesn’t go far, used by some aquatic plants + take it out the water
• Can have systems w/ de-nitrifying towers - remove nitrites
• Small amount removed as N2 gas
• To remove majority of nitrates, will have to do water changes

Question 4

Causes of spikes in NH3/nitrates/nitrites

Answer 4

• 1). Failure to prepare + mature a tank + filter - bacteria need to be implanted into system + build-up its numbers, prepare tank
• Filter before introduce fish using filtration material from another tank to populate the filter or commercial liquid populations to put on sponges -> run tank w/ organic material e.g. fish food and allow to stabilise for few w
• 2). Overstocking - can be gradual as fish grow/breed, may be too small filter
• When sudden inc in no. fish by new group + don’t allow filter to adapt
• 3). Failure of filter - stop water circulating, place AB -> kill all bacteria
• 4), Overload or organic material -> overfeeding, algal or plant bloom, dead fish
• Inc feed
• Algae die -> inc release of organic matter

Question 5

Consequences of spikes in NH3 (first stage)

Answer 5

• 1). Irritation of skin - discomfort, ulceration, inc risk of skin infection
• Become more active + twisting in water/rubbing against side of tank/pond
• Ammonia burns
• Abrasions - rubbing against things
• Skin infection - barrier of skin damaged + opportunistic bacteria can take advantage + cause ulceration + infection
• 2). Gill epithelial hyperplasia - 2y effects on oxygenation -> resp signs, reduced osmosis + NH3 excretion
• Thickened gills - don’t have effective diffusion - less O2 pass over -> hypoxia
• More vulnerable to hypoxic stress
• Resp signs
• Dec excretion of toxins
• 3). General debilitation due to chronic stress

Question 6

Consequences of spikes in nitrites (NO2-)

Answer 6

• Inc nitrite absorption
• Hb oxidised to methaemoglobin - doesn’t carry Hb as efficiently
• Hypoxia due to reduction in O2 transport
• Pale tan mucosa + gills

Question 7

Consequences of spikes in nitrates (NO2^3-)

Answer 7

• Rarely clinical in itself - not particularly toxic
• May affect eggs + fry - juveniles affected, may affect fertility + development of fry
• Facilitates algal + plant bloom, only produce O2 during the day - 2y drop in oxygenation - use up O2 overnight -> O2 crash = sudden die-off -> sudden release of organic material

Question 8

Water quality management

Answer 8

• Water changes - 30 - 50% of tank pond vol, don’t replace w/ normal tap water, chloramines will wipe out filter bacteria + toxic to fish, need sample of pre-prepared water, allowed to age + allows chlorine gas to diffuse out or Tx water w/ commercial products to remove chlorine + chloramine
• Add zeolite to bind NH3 + immediately removes from water, but cannot leave in place or NH3 released bak out into water, take out + place in salt water + reuse = temp sink for NH3
• Reduce organic load - remove algae + plants overgrowth, reduce feeding - can just stop feeding for few days
• Remove debris - siphoned out but be aware of dec water quality
• Improve oxygenation - aerate water, cool or shade water if hot weather - will hold more O2 at cooler temps - ice bottles or adding colder water

Question 9

Longer term water quality management

Answer 9

• Identify + manage cause
• If fish died = remove, simple matter
• Allow filter maturation - re-populate
• Inc filter capacity
• Reduce stocking of plants or fish

Question 10

Low O2 saturation

Answer 10

• 1). High biomatter load - algae, fish decomposing vegetation - plants overnight when CO2 production continues + no O2 produced
• 2). High temps - O2 saturation dec w/ inc temp
• Severe issues

Question 11

Low O2 saturation - CS + Dx

Answer 11

• 1). Die off - early morning when O2 lowest
• 2). Fish gathering at point of aeration - trying to suck in air at surface
• Failure of normal diffusion - gill damage, or not enough O2
• 3). Signs of chronic stress - ulcerative skin disease, mortality of already compromised fish
• Dx - measure O2 saturation at sunrise
• Lower mortality at milder stages - those already compromised e.g. tumours are the ones that die first but still down to O2

Question 12

Low O2 saturation - managment

Answer 12

• Remove biomass - stable oxygenation throughout day + night
• Inc aeration e.g. hose at height, fountains, waterfalls, commercial - depends on size of the enclosure, aeration stones in small tank
• Dec stocking density - relocate permanently/temporary removal until dealt w/ 1y issues
• Provide shade/cool water
• Monitor nitrogen processing - NH3 + nitrites also inc due to common factors

Question 13

Ulcerative skin disease - parasitic

Answer 13

• Common in koi
• Protozoa - Ichtypthirius multifillis (Ich) - small white spots + irritation of fish - rubbing + showing irregular movements
• Gyrodactylus skin flukes
• Dactylogyrus gill flukes
• Argulus lice
• Lernea anchor worm -> focal irritation
• Then can get 2y bacterial infection due to injury to skin

Question 14

Ulcerative skin disease - bacterial (1y infection)

Answer 14

• Aeromonas spp most common - diffuse reddening + 2 y ulceration when skin sloughs off
• Range of environmental bacteria can be opportunistic invaders - Pseudomonas - when got skin surface damage
• Primary bacterial infection rare - commonly 2y: trauma, damage to skin barrier e.g. high NH3

Question 15

Skin disease - viral

Answer 15

• Rarely ulcerative
• Cyrpinid herpes
• Can be ulcerative but typically presents w/ raised plaques
• Not great deal to Tx - will remain infected
• Will see viral flares - cold, dec immune system but low mortality

Question 16

Skin disease - fungal

Answer 16

• Typically 2y
• May be ulcerative
• Can present as ‘fluffy’ growths
• Fungi within water colonise
• White or greeny-brown colour

Question 17

Approach to ulcerative skin disease - investigation

Answer 17

• Assess pond/tank side where possible - samples brought into the clinic will deteriorate over time, diff temps + conditions
• Test water parameters - NH3, nitrites, O2
• Assess individual fish for gross lesions + macroscopic parasites
• Severity + location of lesions
• Normal fish - any minor changes?
• Collect swab samples for culture
• Collect scrapes for cytology/parasitology - examine immediately if possible

Question 18

Ulcerative skin disease - Tx

Answer 18

• Medication for specific cause - in main tank/pond or in isolation tank
• Consider adding low-dose salt to reduce osmotic stress - 1 - 2 g/L, can improve overall fish health
• Manage water quality carefully
• Reduce stressors

Question 19

Medication admin of fish medicine

Answer 19

• Orally - compound into pelleted or gel food (set in ice cube trays - indv Tx) - oxytetracycline for koi + pond fish
• Can create own mix
• Injections - epaxial muscles either side of dorsal fin, hard to restrain (stressful)
• In water - dissolve/dilute, bypass filtration system - remove bacteria/take fish out until cleared out bacteria, powder/liquid directly y in water then return to normal pond
• Short term dips of higher conc
• Temp affects dosing requirements + freq

Question 20

Swim bladder disorders

Answer 20

• Goldfish
• Altered buoyancy - suggestive, but can be due to GI disease (distension), neoplasia, granulomas (TB) or ascites (renal neoplasia)
• Stuck at top/bottom of tank, unable to feed well, bump into walls, abrasions around eyes
• 2y concerns - inability to feed, abrasions
• Infection/anatomical disruption alters swim bladder filling
• Dx - radiographs - highlight swim bladder alterations in position, size or shape
  (Elasmobranchs + some bottom-dwelling teleosts e.g. flounders + some pelagic teleosts e.g. tuna lack a swim bladder)
• Physoclistous species - marine teleosts, cichlids, bass + sunfish - gases diffuse into swim bladder from rete mirabile - bloodstream ‘gas glands’
• Physostomous species (koi + goldfish, catfish, salmon + trout, tetras) - pneumatic duct connects oesophagus + swim bladder, bacteria, fluid, FB or food can enter swim bladder = more swimbladder issues; koi have rete mirabile as well as duct

Question 21

Swim bladder disorder - Dx

Answer 21

• Radio/US to check for mass or fluid displacing the swim bladder - done consciously, cope for short periods w/o water, put in dish where cannot jump out in lateral
• Aspirate for culture + cytology -> AB
• US - when fluid/water gets in the way
• V fibrous tissue - hard to interpret mass unless well-defined
• Can instil sterile saline + aspirate back if appears to not have much fluid in swim bladder

Question 22

Swim bladder disorder - Tx

Answer 22

Based on findings
- Systemic antimicrobials - Oxytetracycline to start off before get C&S results back
- AB instil directly into swim bladder but can cause irritation due to presevatives
- Feed larger food items to trigger opening of pneumatic duct to allow equalisation of pressure between swim bladder + oesophagus
- Remove hazards from, if got over distension of swim bladder, feeding goldfish peas to normalise swim bladder
- Adapt environment - remove any decor that they may collide w/ + injury themselves
- Guarded Px - most present well-on in the disease

Question 23

Notifiable disease

Answer 23

• Spring viraemia of carp
• Koi herpes virus
• Contact APHA for advice + testing if high mortality, weird-looking skin/gills

Question 24

Spring viraemia of carp

Answer 24

• Petechial H+ of skin, gills + eyes
• Exophthalmos - protrusion of eyes
• Pallor - of mm
• High mortality

Question 25

Koi herpes virus

Answer 25

• Anorexia, lethargy
• Gill necrosis
• Skin pale patches
• Erratic swimming
• High mortality

Question 26

Tropical freshwater - common conditions

Answer 26

• Water quality issues - if have breakdown of aeration system can lead to O2 depletion but less common as less temp variation + less vegetation overgrowth
• Fin rot (similar pathology to ulcerative skin disease)
• Conspecific and intraspecific trauma - deplete numbers when grow in size
• Mycobacterium marinum - zoonotic, occasional issues
• Lymphocystis
• White spot (Ich)
• Fungal skin disease
• Velvet (Piscinoodinium)
• Hole in the head (Hexamita)

Question 27

White sport (Ich)

Answer 27

• Protozoa - Ichthyophthirius multifilliis
• < 1 mm, appear as fine white dots over skin and cause
• 2y dermatitis
• Inc mucus, ulceration
• Gill damage pos -> more sig signs when damages diffusion

Question 28

White spot (Ich) - Tx

Answer 28

• Over-the-counter copper-based water treatment
• UV filtration of water will reduce protozoal replication + breaks lifecycle
• Raise temps to 30 C over 48 - 72 h to reduce protozoal replication + kill them off a bit faster
• 1g/L salt added into water -> dec stress

Question 29

Mycobacterium marinum (TB)

Answer 29

• All fish species, causes
• Ulcerative skin disease, less common
• Visceral granulomatous form, most cases, only find out PME - lethargy, anorexia, loss of condition, coelomic distension, but lose of muscle + overall condition
• Dx - identification on biopsy of skin lesions of histopath of granulomas at PME
• Slower progression
• Impossible to erradicate from shoal
• Depopulate, disinfect, dry out tank
• Quarantine new fish for 2 m

Question 30

Hole in the head

Answer 30

• Affects cichlidae (cichlids, discus + Oscars)
• Presents as shallow ulcers on head + sides
• Due to Spironucleus flagellated protozoa (catfish - Edwrdsiella ictaluri -> head ulcers)
• Mortality low but may be part of chronic stress or co-morbidity w/ higher mortality, presents when other issues going on
• Metronidazole given in food or in water (less effective) but recurrence occasionally seen, repeat Tx
• In catfish - Edwardsiell ictaluri causes head ulcers = similar presentation but Tx w/ AB

Question 31

Marine tropical - common diseases

Answer 31

• Water quality issues
• Cryptocaryon (similar to Ich protozoal)
• Marine velvet (Amyloodinium)
• Lymphocystis

Question 32

Lymphocystis (Irdovirus)

Answer 32

• Marine angelfish, butterfly fish + clownfish; cichlids (brackish/freshwater)
• Viral infection causes fibroblasts to balloon in size
• Hypertrophied cells of 1 mm diameter are visible as white dots
• Disfiguring but low mortality
• Lesions recur spontaneously but relapse is pos at times of stress
• Tx/management - accept endemic lymphocystitis or cull affected animals