Synchronization of daily rhythms of locomotor activity and plasma glucose, cortisol and thyroid hormones to feeding in Gilthead seabream (Sparus aurata) under a light–dark cycle

May 4, 2010Physiology & behavior

Daily rhythms of movement, blood sugar, stress, and thyroid hormones linked to feeding in Gilthead seabream under light-dark cycles

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Abstract

Gilthead seabream exhibited 86% of their total daily locomotor activity synchronized to feeding time.

Fish adjusted their locomotor activity based on when food was provided, with daytime and nighttime activity corresponding to feeding time.
Blood glucose levels showed a strong synchronization to feeding time, peaking 8 hours after meals in both groups.
Cortisol levels rose after feeding, with fish fed at mid-dark maintaining higher levels for 8 hours compared to those fed at mid-light, who returned to baseline within 4 hours.
Average daily cortisol values were significantly higher in fish fed at mid-dark compared to those fed at mid-light.
Delaying feeding by 12 hours resulted in a corresponding shift in the daily glucose rhythm and notable changes in cortisol levels for mid-light fed fish.

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Food availability is far from constant but tends to be cyclic, and fish therefore show a variety of circadian rhythms which can be entrained to feeding time. The aim of this study was to investigate the synchronization to mealtimes of behavioral (locomotor activity), metabolic (glucose) and endocrine (cortisol and thyroid hormones) daily rhythms in gilthead seabream. To this end, fish were reared under a 12:12 LD cycle and fed 1% of their body weight once a day either at mid-light (ML) or at mid-dark (MD) of the LD cycle. Fish synchronized their locomotor activity to the phase in which food was delivered, ML and MD fish displaying 86+/-3% and 81+/-1% of their total daily activity during daytime and nighttime, respectively. Daily variations of blood glucose were strongly synchronized to feeding time in both experimental groups, peaking 8h after the meal. A postprandial cortisol peak was observed in both groups. In fish fed at MD the cortisol values were high during the 8h following feeding, whereas in fish fed at ML cortisol levels returned to basal values within 4h. In addition, MD fish showed a higher average daily cortisol value (24.75+/-2.65 ng/ml) than ML fish (10.30+/-2.18 ng/ml). Feeding time affected the magnitude of daily variations in the thyroid hormones. When the time of feeding was delayed by 12h, a shift of the same magnitude could be observed in the glucose daily rhythm and a dramatic change in the cortisol levels of the ML-fed group compared with results mentioned above. In summary, gilthead seabream synchronized their locomotor activity to the phase when food was provided and showed different degrees of synchronization of their behavioral, metabolic and endocrine rhythms to feeding time. Since these parameters are used to evaluate stress responses and welfare in seabream, their daily rhythm and synchronization to light and feeding time should be taken into account.

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Synchronization of daily rhythms of locomotor activity and plasma glucose, cortisol and thyroid hormones to feeding in Gilthead seabream (Sparus aurata) under a light–dark cycle

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