Fish Neurology

Question 1

Describe the causes of circling or spiraling in fish.

What are the clinical signs in these fish?

What are some of the potential etiologies? Nutritional? Infectious? Toxic?

How should these fish be worked up?

Answer 1

Circling or Spiraling

• Spiral swimming also called corkscrew or whirling)
• Pruritis can look neurologic - consider parasites or irritants
• Most commonly toxic and infectious

Clinical signs

• Changes in posture: listing, head-down, tail-down
• Behavior: spy-hopping
• Feeding: missing food strikes
• Paralysis or paresis, unilateral or caudal
• Seizures have not been specifically reported in fish
• Blindness hard to evaluate but most fish should show a startle response to a sudden movement above the water

Etiologies: most commonly Vibrio or Streptococcus and myxozoan infections in the CNS

• Developmental
• Metabolic: acid-base, glucose, electrolyte changes
• Neoplasia: nervous system or musculoskeletal
• Nutritional: deficiency of Vit E, several Bs, selenium, calcium or phosphorus
• Vascular: ischemic or vascular event
• Infectious/inflammatory: septicemia, meningitis, encephalitis, myositis
  
  • Viral: betanodaviruses, rhabdoviruses, herpesviruses, birnaviruses, ranaviruses
  • Bacterial: vibriosis, Edwardsiella, Carnobacterium, Serratia, Streptococcus, Francisella, Flavobacterium psychrophilum
  • Fungi/fungi-like: Exophiala, Microsporidia
  • Protozoa: scuticociliates
  • Metazoa: philometrid nematodes, digenes
  • Myxozoa: Myxobolus cerebralis
• Idiopathic: chronic liver or kidney disease
• Toxic
  
  • Ammonia
  • Chlorines
  • Heavy metals
  • Drug toxicity
  • Pesticides, herbicides
  • Paint fumes
  • Cyanide
• Trauma: spine, head, electrical stunning
• Life support system/environmental
  
  • Stereotypies
  • Inappropriate enclosure shape
  • Stray voltage/poor electrical grounding
  • Lightning strike

Diagnostic highlights

• Check water quality especially ammonia, copper, and chlorine
• Differentiate from pruritis or musculoskeletal and swim bladder pathology
  
  • With CNS, fish often show no effort to correct posture
  • Buoyancy is often not affected
  • Signs are often continuous or triggered by a visual or tactile stimulus