WWW.WAS.ORG • WORLD AQUACULTURE • JUNE 2016 31 these preliminary results indicate that the daily pattern would have a certain independence of meal time. Moreover, the residence time of ingested food in different segments of the digestive tract in juvenile fish is a key factor for efficient digestion, depending on the feeding strategy and the species-specific internal digestion process during the day. As in the case of the larval stage, the information on this issue is still too fragmentary to build a global picture of the whole process over a 24-h cycle. More research is needed to confirm that, independent of feeding protocol, the digestion process in the intestine occurs mainly in a 24-h period, as observed in the stomach. In summary, the process from feed intake to nutrient absorption is regulated at the molecular level with a daily schedule of different biological tasks. This program can be modulated to obtain the greatest benefit at the least cost when food is offered at the adequate time. Our current knowledge, based primarily on only one single sample taken over 24 h, gives erroneous information given the high daily variation. For this reason, we need to fill this knowledge gap in different farmed species and to establish feeding and digestion rhythms in relation to a variety of feeding protocols. The next steps in this research are to combine evaluation of feeding frequency with variation in the amount of food offered. Should we always offer the same amount of food in each meal during the day? Notes Manuel Yúfera, Instituto de Ciencias Marinas de Andalucía (ICMAN-CSIC), Campus Universitario Río San Pedro, 11519 Puerto Real, Cádiz, Spain; manuel.yufera@icman.csic.es Acknowledgments Project: Ridigest AGL2011-23722 (Plan Nacional I+D+I , MINECO, Spain + ERDF/FEDER) References Mata-Sotres, J.A., G. Martínez-Rodríguez, J. Pérez-Sánchez, F.J. Sánchez-Vázquez and M. Yúfera. 2015. Daily rhythms of clock gene expression and feeding behaviour during the development in gilthead seabream, Sparus aurata. Chronobiology International 32:1061-1074. Mata-Sotres, J.A., F.J. Moyano, G. Martínez-Rodríguez and M. Yúfera. 2016. Daily rhythms of digestive enzyme activity and gene expression in gilthead seabream (Sparus aurata) during ontogeny. Comparative Biochemistry and Physiology Part A, Molecular & Integrative Physiology 197:43-51. Navarro-Guillén, C., F.J. Moyano and M. Yúfera. 2015. Diel food intake and digestive enzyme production patterns in Solea senegalensis larvae. Aquaculture 435:33-42. Yúfera, M., F.J. Moyano, A. Astola, P. Pousão-Ferreira and G. Martínez-Rodríguez. 2012. Acidic digestion in a teleost: Postprandial and circadian pattern of gastric pH, pepsin activity, and pepsinogen and proton pump mRNAs expression. PLoS ONE 7(3) e33687. Yúfera, M., M.J. Romero, I.M. Pujante, A. Astola, J.M. Mancera, F.J. Sánchez-Vázquez, F.J. Moyano and G. Martínez-Rodríguez. 2014. Effect of feeding frequency on the daily rhythms of acidic digestion in a teleost fish (gilthead seabream). Chronobiology International 31:1024-1033. Yúfera, M., C. Navarro-Guillén, J.A. Mata-Sotres, F.J. Moyano and G. Martínez-Rodríguez. 2015. Digestive rhythms in fish larvae and juveniles. From molecular gene expression to enzymatic activity. World Aquaculture 2015, Jeju island (South Korea), 26-30 May 2015. LEFT, FIGURE 6. Some examples of the filling of stomach and intestine over 24 hours in juvenile fish fed one single meal or several daily meals. Modified from Yúfera et al. (2014) and Yúfera et al. (2015). RIGHT, FIGURE 7. Changes in gastric pH and pepsin activity when gilthead seabream juveniles are fed with different feeding frequencies but maintaining the same daily ration. Gastric acidification and pepsin activity is higher when the food supply is more frequent. Numbers within the small squares indicates the maximum pepsin activity in each case. Modified from Yúfera et al. (2014).
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