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Temperature resistance and thyroid activity in goldfish maintained under controlled photoperiods Robertson, Georgina Beth


Temperature resistance was measured in goldfish which had been maintained under controlled photoperiods during different seasons over a twelve month period. A consistently higher heat resistance was found in fish which had been kept under the longer photoperiod. The cold resistance of short-day fish was greater than that of long-day fish in the fall and winter, but in the spring and summer the relationship seemed to be reversed. Thyroid uptake of radioiodine was determined in fish which had been subjected to the same photoperiod treatment. Short-day fish showed a consistently higher uptake of I¹³¹ , although the differences were not statistically significant. Photoperiodically adapted fish treated with thyroxine or TSH showed increased resistance to cold. Thiouracil caused the reverse effect, but thiourea caused increased resistance in the long-day group. Tissue cholesterol analyses were carried out on fish treated with thyroid materials. Gonad weight/body weight relationships were compared in fish maintained under the two photoperiods to determine possible correlations between the state of sexual maturity and thermal resistance.

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