Metabolic responses of fresh-water sunfish to seasonal photoperiods and temperatures

Kurzfassung

Beim Gemeinen SonnenbarschLepomis gibbosus wurden nach Adaptation an 9- und 15stündige Photoperioden und an Temperaturen zwischen 5° und 25° C (Anstiegsintervalle 2,5° C) im Herbst und Winter die Respirationsraten bestimmt. Es zeigte sich, daß die Temperaturadaptation der Atmung in einem bestimmten Temperaturbereich nahezu perfekt ist (Q ₁₀ etwa 1); dieser Bereich wird aber durch eine Veränderung der Tageslänge oberhalb einer kritischen Temperatur von ungefähr 10° C modifiziert. Innerhalb dieser Spanne thermischer Homöostasis war die Atmungsintensität von Langtag-Fischen merkbar niedriger und das Ausmaß der Perfektion der Anpassung etwas größer als bei den Kurztag-Fischen. Derartige tageslängenabhängige Unterschiede wurden an Frühjahrsfischen in Brutkondition nicht gefunden. Die stoffwechselphysiologische Akklimatisation vonL. gibbosus läßt sich auch an Hand der Operculumbewegungen nachweisen; sie ist hier allerdings weniger perfekt (Q ₁₀ etwa 1,3) als im Falle der Atmung und offenbar auch weniger von der Tageslänge abhängig. Unterschiede in der Atmungsintensität von Gehirn- und Kiemengewebe bei verschiedenen Tageslängen und Temperaturen scheinen nur als Folge einer Entkoppelung durch Dinitrophenol aufzutreten. Dieser Sachverhalt deutet auf Aktivitätsveränderungen einiger Komponenten der zellulären Systeme dieser Gewebe hin, welche bei der Adaptation an verschiedene Tageslängen und Temperaturen auftreten und erst nach partieller oder vollständiger Entkoppelung der oxydativen Phosphorylierung limitierend für die Stoffwechselintensität werden.

Summary

1. Metabolic compensations by pumpkinseed sunfish,Lepomis gibbosus, to photoperiods of 9 and 15 hours and to acclimation temperatures ranging between 5° and 25° C have been examined. Respiration rates of whole fish, their brain, gill and muscle tissues, and opercular frequencies were used as indices of adaptation. Techniques for the determination of respiration rates and opercular frequencies have been outlined and discussed.

2. A range in thermal homeostasis has been found forL. gibbosus over which thermal acclimation of respiration is nearly perfect (Q ₁₀ about 1), but which is modifiable by alterations in day length above 10° C. Although less obvious, a relative thermal homeostasis has been detected for opercular frequency as well. Perfection of acclimation appears to be best with both indices in the groups of sunfish which have been adapted to the 15-hour photoperiod.

3. Significant differences in rates of respiration, but not in opercular frequencies, have been observed between the long and short-day groups of fall and winter sunfish above 10° C. During spring and with sunfish in breeding condition, these differences were not detected. Both short and long-day fish showed the same higher level of respiration found to be related to short photoperiod adaptation (9 hrs.). It is suggested that the photoperiodic effect of inducing changes in metabolic rates, most directly relates to some process of conditioning the fish for their primary biological function, reproduction.

4. Because the characteristics and photoperiod sensitivity of metabolic compensations for temperature byL. gibbosus are not apparent below 10° C, this temperature is considered to be critical ecologically for the species in western Massachusetts. The existence of a lower critical temperature for thermal homeostasis of metabolic functions (capacity adaptation) in sunfish is stressed because of its potential as a sensitive indicator of physiological variations for climate and latitude.

5. No indications of compensation for photoperiod (9 and 15 hrs.) and temperatures (7.5° and 20° C) have been detected in the respiration of brain and gill tissues ofL. gibbosus at 25° C except after uncoupling with dinitrophenol. The response of brain respiration with the drug appears to be greatest in sunfish adapted to a 9-hour day and 20° C. In contrast, the dinitrophenol effect upon respiratory change of gill filaments appears to be reversed with respect to the thermal history of the donor fish (highest with acclimation to 7.5° C), but unrelated to the length of the adaptation photoperiod. It is apparent that metabolic systems in different tissues of the same animal or the same tissues in different species, contrast greatly in compensatory responses to temperature and photoperiod. Therefore, the suggestion is offered that the resultant of systemic integration often may be more significantly reflected in responses of whole fishes to changing environmental factors than the possible direct effects of temperature sometimes seen in isolated tissues.