Abstract
The circadian rhythm has a great impact on the growth, metabolism and development of animals, but little is known about the circadian rhythm of marine bivalves. Understanding of the feeding rhythm is of great significance to increase the yield of razor clam Sinonovacula constricta, an economically important bivalve mollusk. The aim of this experiment was to study the effects of circadian rhythm of feeding time on digestive enzymes activities and their gene expression in S. constricta within a light (ZT8-ZT20)/dark (ZT20-ZT8) cycle. The present results showed that circadian rhythm of feeding rate (FR) was highly associated with digestive enzyme activities and relative expression of their genes. The highest values of FR were basically observed in the night from ZT0-ZT2 and ZT6-ZT8, which were significantly higher than those values in the daytime from ZT12-ZT14 and ZT18-ZT20 (P < 0.05). The digestive enzymes activities displayed the highest values at ZT2 and ZT8, and the lowest at ZT14 and ZT20. Among them, cellulase and pepsin were found to have significantly different activities (P < 0.05), rather than amylase and lipase. Notably, the relative expression of digestive enzyme genes shared the similar pattern with the activities of digestive enzymes. The highest values of relative gene expression of amylase (AMY), lipase (LIP), cellulase (CEL), and pepsin (PEP) were found at ZT2 and ZT8 in the night, while the lowest values were found at ZT14 during the day. It is therefore suggested that the biological clock may regulate the process from feeding to digestion. Furthermore, it might be better to feed at night to reduce cultivating cost and increase economic benefits in the farming industry of S. constricta.
Highlights
The circadian rhythm is a 24-h cyclical change in environmental factors such as light and temperature caused by the rotation of the earth, which has an important impact on the physiology and behavior of organisms (Fustin et al, 2013)
The relationship between the activity of digestive enzymes and the feeding pattern has been studied in cockle Cerastoderma edule (Ibarrola et al, 1998), clam Ruditapes decussatus and Venerupis pullastra (Albentosa and Moyano, 2008), and scallop Patinopecten yessoensis (Li et al, 2010)
Amylase (AMY) gene is proved to be involved in the growth of razor clam Sinonovacula constricta and Pacific oyster Crassostrea gigas, while cellulase (CEL) can improve the digestibility of food and synthesize glucose to provide energy for the body (Meenu et al, 2014; Thongsaiklaing et al, 2014; Rong et al, 2015; Liu et al, 2017)
Summary
The circadian rhythm is a 24-h cyclical change in environmental factors such as light and temperature caused by the rotation of the earth, which has an important impact on the physiology and behavior of organisms (Fustin et al, 2013). The feeding rhythm of animals affected by cyclical change factors (e.g., light and tide) is essential for the establishment of scientific feeding mode (Mistlberger, 1994; Sanchezvazquez, 1995; Wang, 2004; Connor and Gracey, 2011). Many activities such as feeding, oxygen consumption and digestion have been used to study rhythmic behavior in European oyster Ostrea edulis, New Zealand cockle Austravenus stutchburyi, clam Saxidomus purpuratus, etc (Morton, 1971; Williams and Pilditch, 1997; Kim et al, 2003). The presence of various forms of pepsin precursors such as pepsin A and pepsin C may be related to food or feeding habits (Carginale et al, 2004)
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