Goldfish retina structure and function in extended cold

Abstract

Poikilotherms that are stored in the cold often do not give normal visual responses. This experiment was undertaken to examine the electrophysiological and morphological changes in the retina during cold stress. Twenty-two goldfish ( Carassius auratus) were placed in a refrigerated aquarium and the temperature reduced from 20 to 6 C (±2) for up to 31 days after which temperature was gradually returned to 20 C. During the period of cold stress and recovery, recordings were made of the electroretinogram, fast retinal potential, and tectal evoked response. Eyes of 22 animals were removed at various intervals for histological examinations. Electrical signals of nine animals were tested during cold stress and recovery to monitor for cold effects on retinal and visual pathway discharge. The temperature of two normal goldfish was reduced from room temperature to 5 C during 2 hr to control for the effect of temperature on visual signals. This resulted in minimal physiological changes. All visual signals nearly disappeared within 14 days of exposure to continuous cold stress. Slow recovery to 20–100% of normal was achieved within 52 days after return to room temperature. Statistical analysis of results from samples of retinal tissue indicated that electrical signal loss and return was paralleled by depletion and restitution of many cone outer segments. The return of visual behavior was correlated with the return of nearly normal complements of cone outer segments.