Fish & Invertebrate Dermatology

Question 1

Describe the outermost layers of the fish integument.

What is the mucus layer composed of?

What is unique about the fish epidermis?

What species produce coious mucus?

What species form mucoid casts for sleeping at night?

What causes epithelial hyperplasia?

Answer 1

• External mucus layer
  
  • Rich in mucopolysaccharides, immunoglobulins, lysozymes, free fatty acids 🡪 mucosal defense system
• Epidermis = epithelial cells, mucous glands
  
  • Thicker in fish w/ no scales
  • Unlike mammals - lacks keratin, all layers capable of mitosis (including squamous)
• Epidermis lacks keratinization except the reproductive tubercles of male cyprinids.
• Outer layer of goblet cell mucus and protoplasma aka glycocaylx or cuticle contains immunoglobulins, lysozyme, and antipathogen effector molecules for defense.
• Some produce copious mucus - eels, catfish, rays
  
  • Slippery, use chamois or flannel cloth to help
• Parrotfish create mucoid casting (cocoon) at night - hand-net catches easier at night
• Epithelial hyperplasia - common, nonspecific response to irritants; can be MF

Question 2

Describe the fish dermis.

What are the various scale types and what types of fish have them?

What species have fine scales?

What species are scaleless?

What species have bony plates within the dermis?

How do the spines of a pufferfish affect surgery?

Answer 2

• Dermis = scales, chromatophores, mast cells
  
  • Chromatophores - color change can imply different physiologic states
    
    • Generalized dark color - stress, disease
    • If only on one side - may indicate visual problem
    • If only caudal, may localize spinal problem
  • Scales embedded w/in pockets of dermal tissue, oriented toward tail
    
    • Scale types - placoid, cosmoid, ganoid, cycloid, ctenoid
      
      • Cycloid, ctenoid most common in teleosts
    • Some large & thick like ganoid scales of arowana/arapaima/sturgeon/tarpon
    • Avoid puncturing w/ needles - removal of scale can lead to osmoregulatory problems, infection (esp. 2º like oomycetes, scuticociliates)
    • For surgery - can remove along incision
    • Some have very fine scales (jacks, tuna), others scaleless (jacks, eels, catfish, elephantfish)
      
      • Scaleless - may be more vulnerable to toxins, medications, direct trauma
    • Some have deciduous scales & shed regularly (herring, anchovies)
  • Some have segmented bony plates w/in dermis (seahorses, pipefish, shrimpfish, trunkfish, boxfish, armored catfish, Plecostomus)
    
    • Injection, incision in soft areas; if must be cut - seal w/ wax
  • Pufferfish - erectable spines from scales w/ overlapping roots - must be cut for coelomic incision

Zoo Path:

• Dermis divided into vascularized stratum spongiosum and dense stratum compactum.
  
  • Also contains scales, chromatophores, and lateral line system.
  • Scale loss represents a true ulcer and potential for microbial invasion.
  • Cycloid scales – Salmonids, cyprinids; oval.
  • Ctenoid scales – Spiny fish i.e. perchids; posterior spines (ctenii) and anterior radii directed from a central focus.
• Hypodermis composed of connective tissue and adipose.

Question 3

What are the epithelial ornamentations on fancy goldfish called? What are they composed of?

Describe the lateral line system - how does it work?

How do some fish achieve transparency?

What group of fish display bioluminescence? How does that apply clinically?

Answer 3

• Some fancy goldfish - overgrowth of head epithelium (wen, hoof) - consists of non-ciliated epithelium w/ goblet cells covering mucinous stroma
• Lateral line - canal w/in integument w/ pores - in canal are neuromasts w/ sensory hairs surrounded by gel material 🡪 sensitive to water displacement and vibration
  
  • Depigmentation common problem
• Transparency feature in some - d/t arrangement of collagen fibers allowing passage of light (glass catfish)
• Bacterial luminescence - Beryciformes group (pinecone fish, flashlight fish)
  
  • Have single species of bioluminescent bacteria (Photobacterium fischeri) in organ under eye
  • Bacteria may be observed by pulling into or covering w/ fold of skin
  • Antibacterial Tx can damage the bioluminescent bacteria

Question 4

Red and erosive skin lesions are common in fish.

What differentials should be considered for a single versus diffuse or multifocal lesions?

What infectious diseases can cause these signs - what viruses? what bacteria? what fungi? what protozoa? what metazoa?

What toxins or life support issues can cause this?

What diagnostics should be performed on these fish? What about deceased fish with these lesions?

How should these fish be treated?

Answer 4

Red/Erosive Skin Lesions

• common in fish
• single lesion and no CS - most commonly due to trauma or focal inflammation
• diffuse or multifocal lesions = systemic inflammation r/o bacterial, parasitic, viral, fungal, or toxic etiology
• focal ulcers or erosions with hyperemia and edema -> inflammatory
• focal ulcers without inflammation -> scale loss or exposure of fascia, muscle, or bone with no hyperemia or edema
• diffuse erythema or hyperemia and multifocal ulcers or erosions ->systemic inflammation
• DDX
  
  • Neoplasia - papillomatosis, dermal sarcoma
  • Infectious/inflammatory
    
    • Viruses - rhabdoviruses (IHNV, VHSV, SVCV), infectious pancreatic necrosis virus, carp edema virus, and some herpesviruses (KHV), ranaviruses, megalocytiviruses
    • Bacteria - vibriosis, Aeromonas, Citrobacter, Pseudomonas, Edwardsiella, Flavobacterium, Tenacibaculum, Yersinia, Streptococcus, Erysipelothrix, Francisella, Mycobacterium, Nocardia, piscirickettsial-like spp.
    • Fungi - atypical oomycetes, Fusarium spp.
    • Protozoa - scuticociliates, Chilodonella, Heteropolaria, Spironucleus, Ichthyobodo spp.
    • Metazoa - monogeneans, copepods, leeches
  • Toxic
    
    • Ammonia
    • Polycyclic aromatic hydrocarbons, organochlorines
    • Drug toxicity (inappropriate drug, contamination, idiosyncratic reaction)
    • Detergents
  • Trauma
    
    • Conspecific or interspecific aggression
    • Abrasions from inappropriate enclosure size, shape, substrate, walls, or décor, or due to startling stimuli
    • Catch or handling trauma
    • Fish spine perforation
    • Positive buoyancy and exposure to air
    • Negative buoyancy and damage from substrate
  • Life support system/environmental
    
    • Sunburn or excess UV light exposure
    • Residual oxidants
    • Inappropriate pH
    • Rapid change in water temperature or high water temperature
• Diagnostics
  
  • Hx
  • Assess WQ
  • Visual exam (fish and habitat)
  • Necropsy of any mortalities
    
    • Cultures - bacterial, mycobacterial, and fungal (blood, liver, kidney)
    • Wet mounts and impression smears (gill, skin, liver, spleen, kidney, gastrointestinal tract, any lesions)
    • Histology
    • Other diagnostics (swabs or tissues for PCR testing for IHNV, VHSV, SVCV, KHV, Yersinia ruckeri)
    • Archive samples (gill, muscle, liver, spleen, kidney, frozen at −20°C (−4°F) or ideally −80°C (−112°F) and fixed in 95% ethanol and electron microscopy fixative)
  • Live fish exam
    
    • skin scrapes of affected areas under direct microscopy and impression smears (DifQuik, Gram, and acid-fast stains)
    • gill biopsies under direct microscopy +/- histology
    • consider biopsies of edges of skin lesions for histo
    • consider blood cultures and cultures from under edges of skin lesions
    • consider endoscopic coeliotomy for biopsies and cultures of liver or spleen
  • Consider diagnostic freshwater or salt water dips (matched to pH and temperature) to look for ectoparasites
• Management Approach
  
  • Reduce or remove any possible sources of trauma
  • Treat infectious organisms
  • Reduce or resolve stressors
  • Consider slightly increasing salinity with freshwater fish or slightly decreasing salinity with salt water teleosts to reduce the osmotic stress
  • Consider analgesia and anti-inflammatory medications, e.g. short courses of corticosteroids
  • If lesions severe and fish do not show rapid improvement with management – guarded prognosis

Question 5

FIsh with light spots or skin lesions are most commonly affected with what two parasites?

What if they look more like plaques? Or cotton? Or bubbles?

What infectious diseases can cause these lesions? What viruses? What bacteria? What fungi? What protozoa? What metazoa? What myxozoa?

How should these cases be diagnosed and managed?

Answer 5

Light skin lesions

• r/o Cryptocaryon irritans (in salt water) and Ichthyophthirius multifiliis (in freshwater)
• diagnostics - skin scrapes and gill biopsies examined under direct microscopy
• DDX
  
  • Small spots - often Cryptocaryon, Ichthyophthirius, sessile ciliates, monogeneans, or Flavobacterium spp
  • Plaques - often viral
  • Cotton-like lesions - often oomycetes or sessile ciliates
  • Bubbles - often gas supersaturation
  • Metabolic - calcinosis cutis or calcinosis circumscripta
  • Neoplasia – cutaneous (papillomatosis, dermal sarcoma)
  • Normal anatomy
    
    • Nuptial tubercles of male cyprinids during the breeding season
  • Infectious/inflammatory
    
    • Viruses - lymphocystis, carp pox, adenoviruses
    • Bacteria - Mycobacterium, Nocardia, Edwardsiella, Streptococcus, Flavobacterium, Tenacibaculum spp., Renibacterium salmoninarum, epitheliocystis or other CLOs
    • Fungi - oomycetes, microsporidian xenomas (Glugea spp.), Mesomycetozoea
    • Protozoa - Cryptocaryon spp., scuticociliates, Amyloodinium spp., amoebic gill disease (SW); Ichthyophthirius spp., scuticociliates, sessile ciliates (e.g. Heteropolaria spp.) (FW)
    • Metazoa - monopisthocotyle monogeneans, digenean metacercariae, turbellaria, leeches, copepods, branchiurans, mussel glochidia
    • Myxozoa - Henneguya spp
  • Trauma
    
    • Venomous fin ray (lionfish) or barb (stingray)
    • Foreign bodies (fiberglass, gravel)
    • Abrasions from inappropriate enclosure size, shape, substrate, walls, or décor
  • Life support system/environmental
    
    • Gas supersaturation
• Diagnostic Approach – see above
• Management Approach
  
  • If no signs of gas supersaturation (microbubbles in water or ocular and skin gas bubbles), increase aeration and water flow; target dissolved oxygen may be 95–100%
  • Reduce or resolve stressors
  • Treat pathogens if found

Question 6

What differentials should be considered in fish with dark colored skin lesions?

What is the most common?

What infectious diseases can cause these signs - what bacteria, fungi, protozoa, and metazoa?

What disease would have the worst signs?

Answer 6

Dark Skin Lesions

• less common in fish than light-colored spots
• most common - encysted digenes
• generally morbidity and mortality from these lesions low and investigation not as urgent as white spots
  
  • Amyloodinium can cause more severe signs
• dark foci or plaques - often chronic
• DDX
  
  • most common differential - encysted digenes
  • neoplasia/hyperplasia
  • normal

§ nuptial tubercles on male cyprinids during breeding season

§ anal fin spots on some male African cichlids during breeding season

· infectious/inflammatory

§ bacteria - Flavobacterium, Tenacibaculum spp

§ fungi – oomycetes

§ protozoa - Amyloodinium spp.

§ metazoan - digenes (Clinostomum spp.), capsalid and monocotylid monogeneans, turbellaria, leeches, nematodes (Huffmanela spp.), copepods, branchiurans

· Trauma

§ venomous fin ray (lionfish) or barb (stingray)

§ foreign bodies

§ abrasions from inappropriate enclosure size, shape, substrate, walls, or décor

Question 7

Describe the differentials and management of fish with pruritus.

What are the clinical signs that indicate a fish is pruritic?

What are the most common causes of these signs?

What infectious diseases should be considered? What bactiera, protozoa, and metazoa?

What toxins should be considired?

How should these cases be managed?

Answer 7

Pruritus

• CS - flashing, clamped fins, erratic or agitated swimming, increased jumping, dyspnea, or tachypnea
  
  • Flashing = fast rub on substrate or décor that many fish show in response to skin or gill irritation
• common presenting sign in fish and often due to ectoparasites or chemical or particulate irritants
• DDX
  
  • Most common - ectoparasites, particularly protozoa, environmental irritants
  • Infectious
    
    • Bacteria - Flavobacterium, Tenacibaculum spp.
    • Protozoa - Cryptocaryon, Ichthyobodo, Amyloodinium spp., scuticociliates, amoebic gill disease (SW); Ichthyophthirius, Ichthyobodo, Piscinoodinium spp., scuticociliates, sessile ciliates (Heteropolaria spp.) (FW)
    • Metazoan - monogeneans, leeches, gastrointestinal nematodes
  • Inflammatory
    
    • Branchitis, dermatitis
    • Enteritis, cloacitis
  • Toxic
    
    • Ammonia
    • Chlorines
    • Drug toxicity (inappropriate drug, contamination, idiosyncratic reaction)
    • Inappropriate pH
    • Detergents
    • Harmful algal blooms
  • Trauma
    
    • Cnidarian nematocysts
• Diagnostic Approach
  
  • See above
  • Fecal to look for intestinal parasites
  • Consider freeze 1L of water in a clean plastic bottle for later analysis for pesticides, drugs if work-up unrewarding
• Management Approach
  
  • Increase aeration and water flow; target dissolved oxygen may be 95–100%
  • If source water considered appropriate (similar temperature, salinity and pH, with no risk of contamination), perform 20–50% water change
  • Reduce or resolve stressors
  • Consider short courses of corticosteroids to reduce the inflammatory response (dexamethasone SP 0.5– 1.0mg/kg IM for 2–3 doses)
  • Treat specific cause if identified

Question 8

Describe the external masses found in fish.

What are the most common masses?

What neoplastic diseases should be considered?

What infectious diseases can produce masses? Viruses? Bactiera? Fungi? Metazoa? Myxozoa?

How should masses be diagnosed?

Answer 8

External masses

• Particularly common in bony fish
• Masses in oral or gular area are most commonly goiters

Etiologies: most commonly neoplastic, esp spindle cell tumors

• Metabolic: calcinosis cutis, circumscripta
• Neoplasia: spindle cell, pigmented, lymphoma/sarcoma, lipoma, xanthoma, papilloma
• Normal anatomy: nuptial tubercles, cloacal protuberances, goldfish wen
• Infectious
  
  • Viral: lymphocystis, carp pox, adenoviruses
  • Bacteria: Edwardsiella, Mycobacterium, Nocardia
  • Fungi/fungi-like: microsporidial xenomas
  • Metazoa: pentastomids
  • Myxozoa: myxozoan pseudocysts
  • Algal granulomas
• Inflammatory: panniculitis, dermatitis, steatitis
• Trauma
  
  • Venomous fin ray (lionfish) or barb (stingray)
  • Foreign body (fiberglass, gravel)
  • Abrasions and hyperplasia
  • Hematomas

Diagnostic highlights

• Scrapes, aspirates, impression smears: dif-quick, gram, acid-fast, other special stains
• Culture
• Incisional/excisional biopsy (skin prep not indicated, fix in formalin, left to heal by second intention unless coelomic exposure)
• Endoscopic or exploratory coeliotomy to look for systemic lesions

Question 9

Describe head and lateral line erosion in fish.

What are some of the proposed etiologies?

Where does the erosion typically occur?

What species are particularly susceptible?

What treatments are there? What appears to be the most effective?

Answer 9

• Lateral Line depigmentation
  
  • Chronic ulcerative dermatopathy of fish, starts at head and lateral line does not go past dermis, aka Head and lateral line erosion (HLLE)
  • Etiology
    
    • Likely multifactorial, suspected nutritional, infectious, toxic [heavy metals, nitrates], environmental [granular AC, loss of micronutrients in water, excessive ozone or UV]
    • Damage to sensory canals in the skin
    • Surgeonfish and tangs, tropical angelfish and butterflyfish in established >3 mo aquariums most likely; in FW - discus, FW angelfish and gouramis most
  • c/s
    
    • Symmetric depigmentation and pitting around sensory canals of the head and/or lateral line, systemically fine, low mortality
  • Dx - visual exam, skin scrapes, fecal to r/o infx/parasites
    
    • Histo shows thinning, ulceration or hyperplasia of the epithelium of the skin, lateral line canals
  • Husbandry
    
    • Resolve stressors, can fully heal over weeks to months
  • Medical tx
    
    • Becaplermin - effective if underlying stressors are resolved
    • Vitamin C oral supplementation
    • Metronidazole to treat flagellates
    • Other reported treatments: naltrexone cream, collagen products topically, misoprostol and phenytoin compounded with gelling agent
  • Prevention
    
    • AC filtration in closed systems for short periods of time
    • Regular water changes in closed systems
    • Diets should be varied, micronutrients provided
• Head and lateral line erosion HLEE syndrome.
  
  • Associated with use of activated carbon in filtration.
    
    • Lesions include depigmentation to pitting to large erosions or ulcerations on lateral line structures of head, opercula, body.
    • Can live for long periods of time.
      
      • Animal welfare concerns, maintaining exhibit-worthy specimens.