Abstract
Salinity preference was determined in male Fundulus grandis during different seasons and after several experimental treatments. The percentage of time spent by individual fish within six compartments along a horizontal salinity gradient was monitored by photographing the position of the fish every 5 min for 6 h. Feral Fundulus grandis preferred water of greater salinity during November (mean salinity preference = 22.2 ± 3.2‰) than during June (13.2 ± 2.6‰). Daily injections of prolactin were carried out for 8 days at 0 or 12 h after daily injections of cortisol in fish kept in continuous light in order to simulate daily rhythms of the endogenous hormones present in fish under winter or summer conditions, respectively. The 0-h relation of hormone injections promoted preference for water of greater salinity (23.9 ± 1.2‰) compared with the 12-h relation (15.7 ± 2.2‰) and with uninjected (15.8 ± 2.3‰) or saline-injected (13.6 ± 2.8‰) controls. Seasonal changes in salinity preference appear to involve a shift in phase relations of the circadian rhythms of cortisol and prolactin.
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