Gill Hyperplasia
Introduction
The gill has several important functions in fish physiology: respiration, nitrogenous excretion and fluid balance regulation.
The anatomic structure of the gills helps in its functions by providing a large and very thin surface. The gill filaments are divided into multiple finger-like projections, the primary lamellae, which in turn are divided into secondary lamellae.
There is usually very little mucus on the gill surface.
The most common reponse of the gill to damage is hyperplasia and hypertrophy of epithelial cells, which results in shortening, rounding and fusion of the secondary lamellae. Sometimes even the primary lamellae are affected.
This severely affects the structure and function of the gills and reduces the surface area available for exchange. This also predisposes the gills to further bacterial colonisation and potential septicaemia.
Excessive mucus production also compromises gill function.
Causes
Any irritation can lead to gill hyperplasia, most commonly from bacteria or parasites or from poor water quality.
The most common causes are as follows:
- Protozoa: Trichodina, Chilodonella, Ichtyobodo
- Parasites: Ichthyophthirius, Amlyoodinium
- Bacteria
- Environmental toxins: ammonia, nitrite, heavy metals
- Poor water quality
- Pantothenic acid deficiency
Clinical Signs
These are primarily of respiratory compromise: rapid opercular movements, lethargy, grouping near inlets, tachypnoea.
Fish may show lesions characteristic for a particular disease.
There will be increased mortality.
Diagnosis
Gill biopsies should be performed on dead fish to examing their gross and histological appearance.
Histology will reveal shortening, fusion and clubbing of the secondary lamellae.
If gill hyperplasia is detected on a wet mount this indicates that severe pathology is present.
Treatment
The underlying cause should be dealt with.
This may include chemical treatment of the water to eliminate parasites, protozoa or bacteria.
Improvement of the water quality is also important and oxygen and toxin levels should be monitored.
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Ornamental Fish Q&A 20 |
References
Noga, E. (2010) Fish disease: diagnosis and treatment' John Wiley and Sons
Rosenthal, K. (2008) Rapid review of exotic animal medicine and husbandry: pet mammals, birds, reptiles, amphibians, and fish Manson Publishing
Roberts, R. (2001) Fish Pathology Elsevier Health Sciences