Gill Hyperplasia

Also known as: Environmental Gill Disease — Bacterial Gill Disease

Introduction

The most common response 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 examine 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.

Gill Hyperplasia Learning Resources
Flashcards Test your knowledge using flashcard type questions	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

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