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To investigate the effect of water temperature on gamete maturation and gamete quality, European grayling (Thymalus thymallus) were held under different temperature regimes prior to spawning. Maturation of males and females and their gamete quality depended strongly on temperature regime. The highest percentages of maturing fish and highest gamete quality were obtained under a creek water temperature regime with natural seasonal fluctuations. In warmed creek water (3-4°C), at a constant temperature of 8-9°C, and under an abruptly increasing temperature, regime maturation rates and gamete quality were reduced. The effect was more pronounced in females than in males. The spawning dates of different wild Austrian grayling populations were also correlated with water temperature data collected during the last 10-15 years. The mean spawning date expressed as the number of days from 21 December until spawning ranged from 98 to 111 days for lower elevation populations, while it was considerably delayed for an alpine population. All populations spawned at water temperatures of 5.5-7.2°C. Regression analysis indicated that spawning date correlated with (1) the overall mean water temperature from 21 December until spawning, (2) the mean water temperature during both the last 10 days and 15 days before spawning, and (3) the difference between mean January temperature and that of the last 15 days before spawning. The regression functions indicate that an increase in water temperature from 21 December to spawning of 1°C advances spawning by 5½ days, and an increase of 1°C in the last 10-15 days advances spawning by 3½ days.

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The present study investigated the effect of various temperature regimes on embryonic and yolk-sac larval development of the burbot Lota lota. At constant temperature regimes a high percentage of ready-to-hatch embryos, hatched larvae and normally shaped larvae was observed at the lowest temperature (2° C), which significantly decreased with increasing temperatures (4 and 6° C). No larvae hatched at 9° C. The stream temperature regime had no effect on the percentage of ready-to-hatch embryos, but significantly decreased the percentage of hatched larvae and of normally shaped larvae. The lake temperature regime did not affect the viability variables. Also an abrupt temperature increase from 2 to 4° C after 8 days and from 2 to 9° C after 48 days had no effect on the evaluated viability variables. For yolk-sac larvae no temperature related mortalities or abnormalities were observed between 2 and 9° C.