Table 2.
Important and common noninfectious diseases, including neoplasms of zebrafish. Facilities: mean annual prevalence in facilitates based on data from 2006–2018 (752 cases involving 10,121 fish). ND = not determined.
| Lesion or Disease | Facilities (%) | Pathology | Clinical Signs | Causes | Impact |
|---|---|---|---|---|---|
| Gill lesions | 23 | Epithelial hypertrophy and hyperplasia. Fusion of secondary lamellae in severe cases | Respiratory distress, may only occur when stressed | Poor water quality (ammonia, nitrite, nitrates). Occasionally bacteria present, but generally secondary to poor water quality | Respiratory distress and mortality if severe. Ammonia toxicity associated with immune suppression, decreased growth, and mortality |
| Egg-associated inflammation | 47 | Degenerating egg material and inflammation in the ovary | Usually subclinical, distended abdomen, rarely external ulcers | Unknown, regular spawning recommended as possible prevention | Severe lesions likely reduce egg production and fecundity |
| Nephrocalcinosis | 21 | Dilation of renal ducts and tubules with calcium deposits | Subclinical | High dissolved CO2, low O2,↓ Mg, ↑ Se and As | Usually subclinical, diagnosed post-mortem. Impaired renal function and growth noted in other fish. |
| Spinal deformity | 18 | Various spinal abnormalities (malformation, dislocation, fracture, dysplasia, neoplasia, degeneration) | Kyphosis, lordosis, scoliosis, platyspondyly | Environmental, genetic, dietary, toxins, infectious agents | May alter swimming behavior |
| Operculum malformation | ND | Outward or inward curling and shortening of opercular flap(s) | Operculum fails to completely cover gill cavity and gills are visible | Unknown, postulate genetic, dietary, and environmental factors | May decrease growth rate and impair ability to cope with poor water quality and respiratory challenge |
| Supersaturation | ND | Gas emboli in tissues may be visible grossly or in histological sections | Highly variable; bubbles in tissues (esp. eyes and fins), exophthalmia, altered buoyancy, lethargy, ↑ respirations at bottom of tank, mortality | Exposure to supersaturated water | ↓ growth, secondary infections, mortality |
| Hepatic megalocytosis | 26 | Greatly enlarged hepatocyte nuclei and cytoplasmic elements. Multi-nucleate hepatocytes may be present | Subclinical | Xenobiotics, toxins, idiopathic | Effects on hepatic physiology unknown |
| Biliary and pancreatic duct proliferative lesions | 21 | Ductal hyperplasia, dysplasia, and neoplasia | Subclinical | Unknown, higher prevalence of bile duct hyperplasia in TL line | Unknown |
| Seminoma | 20 | 1)Benign spermatocytic or hyperplasia (most common) 2) Mostly earlier sperm developmental stages (oocytes may be present) 3) Dysgerminomas (aggressive and infiltrative) |
The most common type of seminoma is typically subclinical, but may result in abdominal distention | Possible hormonal influence. Have been associated with carcinogen exposure | Unknown, space occupying changes |
| Ultimobranchial tumors | 9 | Hyperplasia, adenoma, and adenocarcinoma | Subclinical | Unknown. Theoretically, electrolyte and osmotic imbalances could stimulate hyperplasia | Unknown |
| Chordoma | 2 | Tumors of notochord remnants typically occur in intestine, less commonly in axial skeleton | Subclinical | Unknown | Tumors in intestine could disrupt digestion. Spinal deformity possible with axial skeleton tumors. |
| Peripheral nerve sheath tumors | 8 | Soft tissue sarcoma; storiform pattern, bundles and streams of spindle cells | Varies with location of tumor; swelling, emaciation, exophthalmia, lethargy | Unknown | Impact may vary with location of tumor |
| Lymphosarcoma | 4 | Monomorphic, round, basophilic cells invading tissues, often in epithelial tissues (skin, mouth, and gills) | Emaciation, skin pallor, “lionhead”, edema, exophthalmia | Unknown. | General declining health |
| Thyroid tumors | 2† | Hyperplasia (simple, ectopic, and nodular), adenoma, and adenocarcinoma distinguished by cellular atypia, mitotic index, and aggressive growth | Red masses between ventral mandibles and in ectopic locations | Iodine deficiency can instigate hyperplastic growth | Thyroid hormone can affect sex ratios of progeny. Unknown if thyroid tumors skew hormone levels enough to have this effect. |
†
This number increases to 3% when considering additional facilities with reports of thyroid hyperplasia and suspect thyroid adenoma.