The effects of prolonged exposure to cold on visual cells of the goldfish

Abstract

Adult goldfish were maintained at 6±1°C (cold stress) for up to two months. Changes in their visual cells were then studied by microscopy and autoradiography. Under normal conditions the length of visual-cell outer segments remains relatively stable because the addition of new membrane components balances the disposal of used membranes. During prolonged exposure to cold, however, outer-segment length decreases significantly. The length of cone outer segments averaged 68% of normal after one month, and 44% of normal after two months at 6°C. The cone outer segments recovered their normal dimensions within two weeks after water temperature was raised to 24±2°C, following one month at 6°C. The length of rod outer segments decreased less than that of cones, averaging 89% of normal after one month, and 72% of normal after two months at 6°C. Cytoplasmic vesicles, probably autophagic vacuoles, increased in number and size during cold stress, and returned to normal within two weeks of recovery at 24°C. Evidently, the shortening of visual-cell outer segments during cold stress reflected an imbalance between the rate of disc formation and the rate of disc elimination by shedding. Upon warming to room temperature, formation of new membrane exceeded loss by membrane shedding, resulting in growth until normal length was attained. Thereafter, length was maintained by a balance between formation and shedding of membrane.