Fish & Invertebrate Musculoskeletal Disorders

Question 1

Describe the skeletal system of fish.

What is the most common type of bone in bony fish?

How does it differ from mammalian bone?

Describe teleost skulls.

What is hyperostosis? Is it pathologic?

Describe the ribs of teleosts.

Describe the various fin types adn functions in fish.

Answer 1

• Skeleton
  
  • Cellular bone more common in bony fish
    
    • Acellular bone in perch-like fish, bass, sunfish
  • Bone solid and Ca absorption cannot occur locally (fracturs lack Ca reserve for repair)
  • Lack bone marrow - may be some vascular canals, spaces
  • Hyperostosis (aka pachyostosis, Tilly bones) - known in 22 families, most common Atlantic spadefish - not typically pathologic but if large can form sequestrate 🡪 skin ulcerations
    
    • Removal or rongeuring bone underneath can help resolve skin signs
  • Teleost skulls - complex series of bones w/ spp. variability
  • Vertebrae vary across spp.; radiographically have prominent cross representing conical recesses enclosing intervertebral pad, a neural spine, hemal arch, and hemal spine
  • Ribes either pleural (attached to vertebrae) or intermuscular (w/in muscle; salmonids)
  • Fins may be embedded in muscle or boneFirm fin spines common, esp. along dorsal fin
    
    • Some contain venom (lionfish, stonefish)
    • Some fins modified into suckers (lumpfish)
    • Lobe-finned fish - lungfish and coelacanths - muscular fins w/ articulating bone in pectoral fin

Question 2

Describe the muscular system of fish.

What are the two types of muscle - how do they differ functionally?

What is unique about the muscle of scup and icefish?

What teleost species have regional endothermy?

How does electrogeneration work?

Answer 2

• Muscle
  
  • White (fast, twitch) predominates - anaerobic bursts, spring swimming
  • Red (slow) - aerobic swimming, more blood supply - typ. thin band under skin along lateral line and/or dorsal midline
  • Pelagic and more active fish 🡪 more red muscle
  • Drug PK likely affected by muscle type - but impact not well-known
  • Scup - pink muscle 🡪 less myoglobin; Icefish –< yellow muscle d/t lack of hemoglobin
  • Muscle and skin generally in elastic 🡪 injection volume and depth imp. to consider
    
    • IM meds may be more likely to cause lesions, volumes should be small
    • Leakage from injections common
  • Most poikilothermic but few have regional endothermy (tunas, billfish, mackerel spp.)
    
    • Endothermy d/t retes in brain, muscle, viscera 🡪 using red muscle located near vertebral column 🡪 improves digestion, nerve, and muscle activity - important for large predators chasing fast prey in cold waters
  • Electrogeneration possible d/t modified skeletal muscles in FW elephantfish, S. American knifefish, electric catfish
• Musculoskeletal system
  
  • Unlike mammals, numbers of muscle fibers not fixed and increase throughout life.
  • Segregation of white and red muscle fibers.
    
    • White muscle – Short bursts of high speed swimming.
    • Red muscle – Pelagic, long distance migrators i.e. tuna.
    • Pink muscle intermediate.
  • Fish bone lacks the ordered canalicular systems found in mammals and does not appear to serve as a reservoir for regulation of blood calcium.

Question 3

Where is adipose tissue deposited in fish?

How does coelomic versus liver or muscle deposition differ in function?

How does adipose deposition differ in active veruss bottom dwelling fish?

What is a common concern in managed care?

Answer 3

Adipose Tissue

• Lipid deposited 🡪 muscle, liver and in some species brain, under skin
• Coelomic fat 🡪 long-term storage vs. Liver/muscle fat 🡪 easier mobilization
• In active bony fish - tend to be stored in skeletal muscle vs. bottom dwellers 🡪 liver
• Red muscle stores more lipids than white
• Deposits fluctuate seasonally 🡪 less likely to vary under human care
• Over-conditioning common in human care - esp. large, mixed spp. habitats 🡪 use diets, targeted feeding, suitable fasting to help

Question 4

Describe the spinal deformities that are common in fiish.

What is the difference between scoliosis, kyphosis, and lordosis?

What are some of the etiologies of these deformities? What developmental issues have been documented? What nutritional issues? What environmental issues?

How should these cases be worked up and managed?

Answer 4

Spinal deformity

Curvature nomenclature (can be combined)

• Lateral: scoliosis
• Dorsal/convex: kyphosis
• Ventral/concave: lordosis

Common in laval bony fish in aquaculture, sand tigers under human care 3-8 yo

• Concurrent deformities in sand tigers: gingival hyperplasia, curled pectoral fins, transient luxation of lower jaw (“drop jaw”)

Etiologies

• Degenerative: OA
• Developmental
  
  • Genetic
  • Triploidy
  • High water temp, high water flow, low dissolved O2 during development
  • Failure of swim bladder inflation
  • Selective breeding for characteristic deformities (fancy goldfish, balloon kissing gourami, balloon molly)
• Neoplasia
• Nuritional
  
  • Deficiencies: vitamin A, B1, C, E, tryptophan, phosphorus, potassium, zinc
  • Excess vitamin A or E
  • Overfeeding and rapid growth rates
  • Suboptimal fatty acid composition of diet
• Infectious/inflammatory
  
  • Bacterial: Mycobacterium, Streptococcus, Flavobacterium psychrophilum survivors
  • Fungi/fungi-like: Microsporidia (eg. Pseudoloma), Mesomycetozoea
  • Metazoa: digenes
  • Myxozoa: Myxobolus spp.
• Iatrogenic
  
  • Intraperitoneal vaccination using oil adjuvants
  • Local injection site reactions
• Toxic
  
  • Selenium
  • Pesticides, herbicides
  • Heavy metals (arsenic, cadmium, copper, lead, mercury, zinc)
  • Mycotoxins
• Trauma (especially when young)
  
  • Electrical stunning
• Life support system/environmental
  
  • Inappropriate enclosure size or design; short glide distances and reduced time gliding correlate with spinal deformities in sand tigers
  • High CO2
  • Stray voltage and poor electrical grounding
  • Lightning strike

Diagnostic highlights

• Check water quality: esp heavy metals and CO2
• Voltmeter to assess for any stray voltage ideally over 24-48 hrs (may be transient)
• Necropsy with additional testing (rads, CT, culture, archive serum, liver, vertebrae, and muscle frozen for vitamin A, C, E, zinc testing)
• Consider aspirate or biopsy of bony lesions and adj muscle

Management highlights

• Supplement diet with vitamin C, E, and potassium (wide safety index) +/- Vit A, phosphorus, zinc if known deficiency

Question 5

Describe the management of exertional myopathy in fish.

What species are particularly susceptilbe?

What is the pathophysiology?

What are some of the risk factors?

What diagnostics can be performed?

What treatments can be done?

Answer 5

• Exertional Myopathy
  
  • Ram ventilating elasmos (esp blacktip, dusky, bonnethead, Atlantic sharpnose) more susceptible, bony fish susceptible, larger > smaller
  • Exertion → lactic acid, CO2 buildup → fish not able to recover aerobically or buffer blood → acidemia
  • Incr risk with low DO, alkailinity, high water temp, lack of recovery time
  • Reduced swimming, dysp/tachypnea, muscle rigidity, acute mortalities
  • Dx
    
    • Clin path - blood gas and lactate via iSTAT (lactate on venous, arterial or mixed, blood gas on arterial)
      
      • Lactate >5 is concerning
    • Grossly normal, histo - muscle necrosis
  • Husbandry
    
    • Incr DO, water flow
  • Tx
    
    • Ventilation [water pumps, syringes, walk animal thru water], O2, fluids [modify osmolality for elasmos, can use LRS, 5 ml/kg bolus IV, or 30 ml/kg IC slow), vitamin E/Se, Na bicarb
    • Sometimes Ca suppl, steroids
    • Muscle relaxants maybe
  • Prevent - high risk spp, plan manual and chemical restraint carefully, ample recovery time