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D.M. Allen, S. Cooper, L. Shelton, G. Hendricks; A Uniform and Thermo–Neutral Illumination for Study of Light Damage to Fish Retinas . Invest. Ophthalmol. Vis. Sci. 2006;47(13):4558.
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© ARVO (1962-2015); The Authors (2016-present)
We present a "Lumitron" method to minimize behavioral evasion of light exposure by fish in retinal light damage studies while at the same time minimizing thermal absorption.
We used 6–150 watt fluorescent bulbs backed by mirrors arranged symmetrically around a hexagonal 30 gallon aquarium. A transitional dimmer circuit was used to provide artificial twilight. Light measurements showed that horizontal intensity was nearly uniform in all directions and averaged 10,000 lux. To test the efficacy of this apparatus in eliciting light damage, albino and normally–pigmented species of fish were exposed to a standard protocol during which fish were sampled for ocular histology: Rainbow sharks – Labeo erythrurus, oscars – Astronotus ocellatus and channel catfish – Ichthalurus punctatus were given 10 days of dim cyclic light ( 50 lux:12hr–ON/12hr–OFF), 7 days intense Lumitron 20hr–ON/4hr–OFF light, then 20–40 days of dim cyclic light for recovery. The OFF period allowed repeated testing for visual sensitivity of dark–adapted fish during the light damage and recovery phases. In the rainbow shark, we measured visual sensitivity by tracking CW and CCW optomotor swimming responses under scotopic illumination meted through reciprocal neutral–density wedges.
Even at the end of the 20 hr ON period, water temperature under full illumination never exceeded 26oC (2oC above ambient air temp). In rainbow sharks, there was a 2.7 log unit decline in dark–adapted sensitivity of albinos during the 7 days of full illumination, whereas normals were unaffected. The albinos recovered visual sensitivity within 7 days of their return to dim cyclic light. Reduction and recovery of visual sensitivity was correlated with damage and repair to rod outer segments (ROS). By histological comparison only, rods of albino oscars were most severely damaged of the three species, while in albino catfish the degree of ROS damage was least, being inversely proportional to a dorsal–ventral gradient of melanin. Albinos of the latter species are not completely tryosinase –/–. Melanin is variably present in melanosomes of the retinal pigment epithelium in the dorsal ¼ of the retina, but this decreases ventrally, such that little or no melanin protection is observed in the inferior half of the retina.
The results demonstrate the efficacy of a thermally safe method to achieve and monitor species–specific levels of light damage in groups of fish exposed to intense uniform horizontal illumination.
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