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Levels of choroidal body carbonic anhydrase activity and glycogen in farmed halibut
D L Williams1, T Hopcroft, U Pantel
1Animal Health Trust, Kentford, Newmarket, UK.
Insights
Aberrant gas production in Atlantic halibut eyes is linked to high carbonic anhydrase enzyme activity and glycogen levels in the choroid. This research explains ocular abnormalities in farmed fish.
Area of Science:
- Ocular pathology
- Fish physiology
- Enzymology
Background:
- Farmed Atlantic halibut can develop ocular abnormalities.
- Aberrant gas production in the choroidal body is a suspected cause.
- Carbonic anhydrase enzyme activity is implicated.
Purpose of the Study:
- Investigate choroidal body carbonic anhydrase activity in affected and normal halibut.
- Quantify enzyme activity and glycogen levels.
- Correlate findings with ocular abnormalities.
Main Methods:
- Histochemical detection of carbonic anhydrase for microdensitometric quantification of enzyme activity.
- Best's carmine staining and microdensitometry to evaluate glycogen levels.
- Comparison between affected and normal halibut groups.
Main Results:
- Mean carbonic anhydrase enzyme activity was over twice as high in affected halibut compared to normal fish.
- Glycogen levels were significantly higher in affected fish.
- Posterior segment gas bubble and cyst formation correlated with elevated enzyme activity and glycogen.
Conclusions:
- Aberrantly high choroidal carbonic anhydrase activity and glycogen concentrations are associated with ocular abnormalities in farmed Atlantic halibut.
- These factors likely contribute to gas bubble and cyst formation.
- Understanding these mechanisms can inform strategies to prevent ocular disease in aquaculture.
Abstract:
We postulate that ocular abnormalities in farmed Atlantic halibut occur following aberrant gas production in the choroidal body associated with the enzyme carbonic anhydrase. We investigated choroidal body carbonic anhydrase activity in affected and normal halibut. Immunohistochemical detection of carbonic anhydrase allowed neither quantification of enzyme levels nor determination of enzyme activity. Histochemical detection of carbonic anhydrase, however, allowed microdensitometric quantification of enzyme activity. Mean enzyme activity in affected individuals was over twice that in normal fish. Glycogen, which we suggest is used to fuel oxygen production in the choroidal body, was evaluated by Best's carmine staining. Microdensitometry demonstrated glycogen levels of be significantly higher in affected fish. These findings show that posterior segment gas bubble and cyst formation is associated with aberrantly high choroidal enzyme activity and high choroidal glycogen concentrations.