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The effects of photoperiod and temperature on the daily pattern of locomotor activity in juvenile sockeye salmon, Oncorhynchus nerke (Walbaum) Byrne, John Edward

Abstract

Supervisor: N. R. Liley The endogenous and exogenous factors contributing to a diel rhythm of locomotor activity in juvenile sockeye salmon Oncorhynchus nerka (Walbaum) were examined in the laboratory. The basic measure employed in the investigation was spontaneous locomotor activity. High frequency sound (800 kHz) was used as a monitoring technique to collect continuous activity records. Three major areas received attention. First, a description and analysis were provided for the entrained diel activity pattern under three different temperatures (5°, 10°, and 15°C) and three different photoperiods (8L 16D, 12L 12D, and 16L 8D). The combined effects of temperature and photoperiod upon the basic 24 hour response were recorded and analyzed. Juvenile sockeye salmon were nocturnally active immediately after emergence from the gravel. A diurnal activity pattern was gradually acquired during the following 14 days and was maintained for 12 months. Photoperiod was the primary environmental synchronizer for either diurnal or nocturnal activity. The endogenous component of the activity rhythm was examined in constant environmental conditions. Constant light (34.4 lux at 10°C) facilitated the free-running response while constant dark inhibited it. The spontaneous frequency in constant light was 23.30 hours but this could be altered by light intensity or periodic feeding. The final experiments focused upon the relationship between the environmental stimulus (photoperiod) and the physiological sensory mechanisms mediating the entrained response. The eyes were the primary photoreceptors mediating information about the light-dark environment. The entrained activity response disappeared when the retina was not illuminated. When the pineal body was removed or shaded, juvenile sockeye responded with increased activity. Intraperitoneal injections of melatonin (N-acetyl-5-hydroxy-tryptamine) or serotonin (5-hydroxy-tryptamine) selectively altered the activity amplitude in either the light or dark respectively. Juvenile sockeye salmon possess an endogenous circadian activity rhythm which is synchronized by the photoperiodic cycle. The fish are generally light active, except for the period immediately after emergence. However, interactions between daylength and temperature can result in temporary dark active responses. Mediation of the photoperiodic information occurs via the retina, but without transmission by optic nerve pathways. Chemical agents (melatonin and serotonin) produced by the retina and/or pineal might control the activity amplitude in light and dark, thus resulting in the characteristic entrained pattern.

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