Influence of Temperature and Photoperiod on Guanine and Hypoxanthine Levels in Skin and Scales of Atlantic Salmon ( Salmo salar ) during Parr–Smolt Transformation

• Published in: Journal of the Fisheries Research Board of Canada
• Main Authors: Johnston, C. E., Eales, J. G.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 1968
• Subjects: General Medicine; Atlantic salmon; Salmo salar
• Online Access: http://dx.doi.org/10.1139/f68-170; http://www.nrcresearchpress.com/doi/pdf/10.1139/f68-170

The influences of temperature and photoperiod on the purine (guanine, hypoxanthine) levels in skin and scale silvery layers of Atlantic salmon at parr–smolt transformation were assessed by holding 2-year-old parr from December to June under four controlled temperature and photoperiod regimes: NLNT, 8LNT, NL3T, and 8L3T (where NL = naturally lengthening daily photoperiod; 8L = 8-hr daily photoperiod; NT = temperature held at 3 ± 1 C until mid-March and then rising to 14 C in June; 3T = temperature maintained at 3 ± 1 C throughout).From December through to March, levels of both purines increased under all four regimes. From April through to June purine levels continued to increase but were greater under NT than 8T regimes, showing that temperature influences purine deposition. Photoperiod changes did not modify purine levels appreciably. Other factors presumably influence silvering since under 8L3T (sustained "winter" conditions) purine levels more than doubled between December and June. The guanine/hypoxanthine ratio, higher for skin than for scale silvery layers, changed little seasonally and showed negligible dependence on temperature and photoperiod. Visual assessment of the extent of silvering correlated closely with measured purine levels. Increases in the fresh weight of fish were similar under all four regimes but a more pronounced decrease in the coefficient of condition occurred under NT regimes.