Fish & Invertebrate Theriogenology & Neonatology

Question 1

Describe mucometra and ovarian cysts in fish.

What species are particularly susceptible?

What is the etiology of these diseases?

How does normal histotroph differ in appearance from mucometra?

What treatments can be provided?

How can these diseases be prevented?

Answer 1

• Mucometra and Ovarian cysts
  
  • Uterine and ovarian pathology esp mucometra and cystic ovaries are common in female rays
  • Coelomic distension, US to diagnose
  • Tx - sx, hormone therapy or breeding
  • Etiology: rays show aplacental viviparity (ovoviviparity) and are induced ovulators. w/o males present, females will constantly produce follicles and become large and cystic. Ovarian cysts can rupture leading to coelomitis, hemorrhage. The uterus never involutes and produces histotroph and over time becomes filled with dense histotroph (mucometra) and uterine trophonemata become large and irregular.
    
    • Housing w/o males is a risk factor
    • Infectious agents may be found such as visceral larval migrans, mycobacteriosis, or fungi
  • Signalment: female elasmos, esp rays - southern stingrays, cownose rays, white spotted eagle rays overrepresented
  • Clinical findings
    
    • Generalized coelomic distention, can progress for years w/o significant pathology
  • Ddx: pregnancy, mucometra, pyometra, uterine neoplasia, hepatomegaly, obesity, coelomic effusion
  • Dx:
    
    • US_ hypoechoic uterine fluid, thick and irregular uterine wall +/- sloughing of trophonemata, L ovary (active one) large and cystic, +/- coelomic effusion
    • Aspiration of uterine fluid, risk iatrogenic infection. Histotroph normally thick and yellow. In mucometra, histotroph may be clear, bloody, or thick and yellow. Leukocytes, bacteria, parasites, fungi are abnormal.
    • Estradiol higher in affected females.
  • Husbandry
    
    • Consider allowing breeding to resolve pathology if mild
  • Medical tx
    
    • Catheterization or cannulation of the oviduct through the cloaca and cervix allows removal of the uterine fluid, but usually recurs
    • MGA 20 mg/kg IM q30d x 2-3mo has improved ovarian and uterine pathology
  • Prevention
    
    • Allowing female rays to breed periodically MAY reduce incidence
    • Prophylactic ovariectomy may be considered, regrowth of ovarian tissue possible.

Question 2

Describe the management of egg retention in fish.

What are some of the proposed etiologies for retained eggs?

What species are particularly suceptible?

How do these fish typically present?

How are these cases diagnosed?

How are these cases managed from a husbandry and medical point of view?

Answer 2

• Egg Retention (Egg Binding)
  
  • Inability to release eggs from the ovaries, oviducts or uteri, common in human care
  • Insufficient envtal or social cues for spawning, associated with primary or secondary oophoritis
  • Ovariectomy is often required
  • Etiology
    
    • Environmental (inappropriate), nutritional (low essential Fatty acids, inadequate caloric intake, obesity), neoplasia, oophoritis/salpingitis/cloacitis, toxic (heavy metals, estrogens)
  • Signalment
    
    • Oviparous and ovoviviparous fish - esp Groupers, Flatfish, Tetras and Irish Lords, less common in elasmos but examples in sandtigers and some skates
  • Clinical Findings
    
    • Coelomic distention, inappetence, coacal/anal distention or prolapse, cutaneous ulcers/fistulas esp in elasmos
  • ddx : egg retention, obesity, hepatomegaly, neoplasia, pregnancy
  • Dx:
    
    • Aspirates or sx (bony) and US (elasmos)
    • US to characterize
    • Bony fish - FNA or tru cut bx through the body wall - cytology, culture, histology
      
      • Normal follicles are spherical, uniform; old follicles show incr translucency, denser cortical cytoplasm, incr variabl size, content; degenerative follicles show lipofuscin depostes, disintegration and leukocytes
      • Red rubber tube or IVC can be insert into genital pore to get a sample of ovaries in some fish
      • Coelomic endoscopy or ceoeliotomy - definitive
  • Husbandry
    
    • Review spawning parameters, stimulate spawning if focllicles look normal
    • Provide areas for egg-laying
  • Medical tx
    
    • GnRH agonists IM or IC once (salmonid GnRH and domperidone; Ovaprim) may induce spawning
    • Chorulon (hCG) may induce spawning
    • Others reported: carp pituitary extract, channel catfish pituitary extract, PGF-2alpha
    • Stripping under ax in bony fish
    • Ovariectomy required if stripping fails in bony fish
    • Elasmos - removal of ova from uteri via per-cervical aspiration and lavage with saline
  • Prevention
    
    • Prophylactic ovariectomy may be considered

Question 3

Describe the management of dystocia in fish.

What species are commonly affected?

What are some of the proposed etiologies?

How do these animals present?

How are these cases managed?

Answer 3

• Dystocia
  
  • inability/difficulty passing a fetus in ovoviviparous or viviparous species
  • MC in rays (myliobatiformes)
  • Etiology
    
    • Nutritional - inappropriate diet, inadequate food intake, obesity
    • inflammation/infection ie metritis
    • Idiopathic - ie uterine inertia, large fetus, abnormal fetus, malpositioning
    • Life support system/envtal - inappropriate water temp, salinity, substrate, photoperiod, social groupings, seasonal variation, other stressors
  • Signalment: rays, esp cownose and yellow stingrays
  • Clinical findings
    
    • Lethargy, acute collapse, coelomic distention if late term, cloacal edema, hyperemia, d/c
  • Dx: if anticipated gestation length surpassed, cloacal palpation of fetus, ultrasound/rads→ assess viability (HR, movement, signs of degeneration), endoscopy
  • Husbandry - optimize envt, review natural hx
  • Medical tx
    
    • If visible, stingray pups can be pulled manually (beware of barb)
    • If fetus cranial, dilate cervix with digital pressure or cannulate (ie sterile syringe case) to insert padded forceps or hemostats
    • C-section using ventral or paralumbar approach reported
    • Overall success poor, but anecdotally attempts at using oxytocin, relaxinm, PGE-1/misoprostol, estradiol, or PGF2a-dinoprost
  • Prevention
    
    • Regular US monitoring of gravid rays

Question 4

Describe the diseases of fish eggs.

Gelatinous egg masses are more susceptible to what types of disease? How is this treated?

What causes soft egg disease in salmonids?

How close to hatching can you medicate eggs?

Answer 4

Egg Diseases - Noga

• Gelatinous egg mass (cyprinids, ictalurids, other species) – eggs stick together and increase risk for secondary bacterial or water mold infection. Treat with sodium sulfite.
• Soft egg disease (salmonids) – eggs become soft and flaccid during incubation because perforations in shell allow loss of fluid. May be due to bacterial or amoebic infection. Antiseptic treatment may help.
• Polypodium hydriforme – one of the few metazoan parasites that is intracellular; problem in caviar and may affect reproduction
• Temperature shock – when acclimating shipped eggs, don’t increase temperature by more than 0.5C/minute
• Premature hatch – Don’t medicate eggs at least 24hr prior to hatching (at least 3 days for salmonids)

Question 5

What is American foulbrood?

How does it affect honeybees?

How is it diagnosed?

How is it treated? Why is treatment controversial?

Answer 5

• American foulbrood
  
  • Caused by the bacterium Paenibacillus larvae, which infects older, sealed larvae or pupae causing them to decay, which results in a foul odor (sulfurous)
  • Usually leads to the death of infected colonies
  • Hives affected by or lost to AFB should be destroyed to prevent spread
  • Detected in suspect cells (discolored, sunken, perforated, or partially capped cells) by use of the ropiness test, which consists of inserting a toothpick or tweezers and twisting out the cell contents
    
    • confirmed if the cell contents twist and rope out of the cell then spring back into the cell when the strand breaks
  • In many states, AFB is a reportable communicable disease
  • In the US, treatment of AFB is controversial and varies by state
    
    • Does not eliminate P larvae spores and may mask signs of the disease in infected hives making detection more difficult
    • Oxytetracycline is the antimicrobial most commonly used to treat AFB. Lincomycin and tylosin can also be used.