Fish & Invertebrate Emergency & Critical Care

Question 1

What differentials should be considered for acute mortalities in a group of fish?

What are the most common differentials?

What demographics of fish are the most susceptible in these situations?

What clinical signs might you see in some of the other fish?

Answer 1

B1 Acute Mortalities in a Group

• · Often environmental or infectious - common differentials are low DO, ammonia toxicity, bacterial infections, Ichthyophthirius multifiliis, or Cryptocaryon irritans
• · Fish under severe, multiple or chronic stressors and juveniles are more susceptible
• · Variable signs: no signs to skin or gill changes and flared operculi
• · Etiology
• o Following fish editions - ammonia toxicity, bacterial infections, Ichthyophthirius multifiliis, or Cryptocaryon irritans
• o Catch/transport - trauma, barotrauma, ammonia toxicity, low DO, metabolic
• o Metabolic - nephroliths
• o Infectious/inflammatory
• § Viral: rhabdoviruses (IHNV, VHSV, SVCV), IPN, KHV, ranaviruses, megalocytivirus
• § Bacteria: Vibrio, Aeromonas, Citrobacter, Pseudomonas, Edwardsiella, Flavobacterium, Yersinia, Streptococcus, Francisella spp
• § Atypical oomycetes
• § Protozoa: Cryptocaryon, Brooklynella spp. (SW); Ichthyophthirius, Heteropolaria spp. (FW).
• § Metazoa: monogeneans
• o Toxic: ammonia, nitrite, chlorines or chloramines, metal, drugs, pesticides/herbicides, fertilizers, paint fumes, nicotine, detergents, hydrogen sulfide, cyanide, harmful algal blooms
• o Trauma, cnidarian nematocysts
• o LSS/Environmental: Low DO, gas supersaturation, rapid changes (temperature, pH, salinity), electrical or lightning, water loss

Question 2

How shoudl acute mortalities in a group of fish be managed?

What diagnostics should be performed? What samples should be collected?

How should the event be managed?

What can be done to reduce the stress on the fish?

Answer 2

Diagnostic approach

• Assess animals (signalment, % effected, clinical signs) and habitat (water flow, organic material, micro bubbles, possible contaminants)
• Check life support system - assessment for stray voltage should include monitoring for 24-48 hours
• Check water quality - especially temperature, DO, ammonia, salinity, pH, copper, chlorine
• Freeze 1 L water in clean plastic bottle for later analysis (pesticides, cations, drugs)
• If concerned about pesticides - freeze sample of the top sediment or substrate in water bottle or sturdy bag
• Review history - system and animal, new animals, quarantine protocols, feeding behavior, water source and additives, water changes, time and species of mortalities, prior morbidity or mortalities, recent medications, life support changes, recent weather
• Skin/Gill/Fin and Necropsy - fresh best
• If after drug exposure, confirm drug identity, record lot number, acquisition, and save sample (can assess content or purity)

Management

• Remove dead fish asap
• Unless evidence of supersaturation, increase aeration (DO target 95-100%)
• If source water not suspected to be contaminated, 20-50% water change
• Remove dead plants and organic debris
• Manage or treat known problems
• If contamination suspected, consider moving fish with acclimation (contraindicated with severe dyspnea); if in doubt start with one or two then move others
• FW: salt supplementation (2-3 g/L) for osmotic stress reduction
• Unless fish emaciated, reduce feeding
• Cover tank windows to reduce lighting or visual stress
• Consider short corticosteroid course to reduce inflammatory response (dexamethasone SP 0.5-1 mg/kg IM 2-3 doses)
• Consider euthanasia with high mortalities >90% (infectious, toxic)
• Monitor for secondary disease

Question 3

Describe the management of physical trauma in fish.

What are some of the common causes of such trauma?

What fish are particularly susceptible?

What findings might be found on physical exam?

What diagnostics should be performed?

How can husbandry be modified to reduce trauma?

What treatments are recommended?

Answer 3

• Physical Trauma
  
  • Sources: capture, inappropriate enclosure, cohorts
  • Often heal well if appropriate envtal conditions
  • Etiology
    
    • Inappropriate enclosure, decor, transport containers
    • Inappropriate cohorts - bite wounds, chasing
    • Mating in elasmobranchs
    • Rough handling
    • Predation
  • Thermal trauma esp common in seahorses as they perch around heaters
  • Signalment:
    
    • Pelagic fish esp trauma from enclosure
    • Fine or no scaled fish - skin trauma more likely
  • c/s
    
    • Location of wounds can help id the source (ie rostral is more habitat)
    • Blood d/c from gill cavity, cloaca, anus
    • Lethargy, gill pallor with internal trauma
    • Darkening of skin with delineation - spinal trauma
    • Abnormal swimming or buoyancy
  • Dx:
    
    • PE, neuro exam if spinal suspected, cytology of lesion scrapes (direct and stained), CBC, blood culture (r/o systemic), imaging, ultrasound
  • Husbandry
    
    • Modify envt
    • Neural and retinal tissue can regenerate in fish at all ;life stages, improvement seen in first few days
    • Incr DO if hemorrhage severe
  • Medical tx
    
    • Hemostasis with pressure, ligation, hemostatic sponges (gelfoam), electrocautery or infiltration of epi or phenylephrine into wouunds
    • Oral admin of water in marine fish, IVF (isotonic, crystalloids, whole blood [if PCV <10%] , can use IC but absorption variable
    • Oxyhemoglobin IV - an oxygen carrier
    • EPO has been used, does not work in goldfish
    • Weigh analgesia with risk fo further trauma
    • Antibiotics with broad spec (gram neg aerobes MC chosen - enro, ceftaz, florfenicol, amikacin) while C&S pending, less susceptible to secondary infx than other vertebrates
    • Topical tx rarely indicated
    • Flushing rarely indicated
    • Becaplermin gel (Regranex) is a PDGF that can accelerate re-epithelialization - spray onto wound bed after gentle debridement
    • Naltrexone cream - similar wound closure rate to Becaplermin in mammals
    • Misoprostol and phenytoin powder - gelling agent and applied topically
    • Topical antiseptics (iodone) may damage tissues and are NOT indicated
    • Surgical repair rarely indicated - if necrosis, infx, improve apposition, or Gi trauma
      
      • Tail fx on batoids heal better by second intention
      • Xenografts reported in skin and cornea of skin - provides and ECM to accelerate healing/repair
  • Prevention
    
    • Attention to habitats, stocking density, barriers/lids, chemical restraint as needed

Question 4

Describe the management of electrical trauma in fish.

What are some sources of such trauma?

How do these fish typically present?

What diagnostics can be performed in these cases?

How can they be managed or prevented?

Answer 4

• Electrical trauma
  
  • Lightning storms, stray voltage, power surges
  • Spinal fractures, abnormal swimming; prognosis poor if signs are obvious
  • c/s
    
    • Asymptomatic with low level exposure
    • Spinal abnormalities, skin discoloration, acute mortalities
  • Dx
    
    • Voltmeter to measure stray voltage, imaging, hx, necropsy (hematomas or necrosis with spinal lesions)
  • Supportive care, euthanasia, analgesia
  • Prevent: surge protectors, pumps and heat exchangers should be routinely grounded