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Abstract

Goldfish (Carassius auratus) of identical thermal and dietary history were subjected to long-day (16 hours) and short-day (8 hours) light periods. Variation in the ability of these groups to withstand temperature extremes were compared during the fall and winter of 1955 and during the spring and summer of 1956. In the fall and winter group fish exposed to 8 hour daily illumination were consistently more resistant to cold and less resistant to heat while the reverse was true of the 16 hour group. In the spring and summer fish the differences were not as marked and were generally in the opposite direction. In general, the data showed that size as well as sex of the goldfish tested modified the observed resistance. At both seasons, fish exposed to shorter daily illumination had higher tissue phospholipid and cholesterol than those exposed to longer illumination. Phospholipid and cholesterol were also compared in the different sexes.