Fatty Acid Composition and Digestive Enzyme Activities of Rainbow Trout in Response to Dietary Docosahexaenoic Acid (DHA
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Fatty Acid Composition and Digestive Enzyme Activities of Rainbow Trout in Response to Dietary Docosahexaenoic Acid (DHA) and Eicosapentaenoic Acid (EPA) During Salinity Acclimation HUANG Ming1), ZHOU Yangen1), *, GE Jian1), AGUSTSSON Thorleifur2), 3), LI Li1), GAO Qinfeng1), 4), and DONG Shuanglin1), 4) 1) Key Laboratory of Mariculture (Ocean University of China), Ministry of Education, Qingdao 266100, China 2) NORCE Norwegian Research Center, Mekjarvik 12, 4072, Randaberg, Norway 3) RORUM Brynjolfsgata 5, 107, Reykjavík, Iceland 4) Function Laboratory for Marine Fisheries Science and Food Production Processes, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266235, China (Received January 24, 2020; revised May 8, 2020; accepted September 1, 2020) © Ocean University of China, Science Press and Springer-Verlag GmbH Germany 2020 Abstract This physiological study aimed to evaluate the effects of dietary docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) on the fatty acid composition and digestive enzyme activities of rainbow trout (Oncorhynchus mykiss) during salinity acclimation. Rainbow trout with an average initial weight of 90.61 g ± 9.25 g were fed diets with the quantities of DHA and EPA equaling to 0.54%, 0.95%, 1.40% and 1.79% (abbreviated as DE-0.54, DE-0.95, DE-1.40, and DE-1.79, respectively) for eight weeks, after which the gastric and intestinal fatty acids composition were analyzed. Subsequently, the fish underwent salinity acclimation. On days 1, 4, 7, and 14 after the freshwater was replaced by seawater and at the end of the 8-week period, gastric and intestinal digestive enzyme activities were determined. The results showed that the gastric and intestinal DHA and EPA contents of the fish were positively correlated to their dietary DHA and EPA levels. Low dietary DHA and EPA levels inhibited the protease activity of rainbow trout. Fish in the DE-0.54 group increased the lipase activity to enhance the utilization of lipids maybe due to the inadequate essential fatty acids for fish in this group. Hence, rainbow trout in the DE-0.54 group failed to maintain suitable activities of digestive enzymes after salinity acclimation. Therefore, a diet with minimum 0.95% DHA and EPA levels is necessary for rainbow trout during salinity acclimation. Key words
digestive enzymes; docosahexaenoic acid; eicosapentaenoic acid; rainbow trout
1 Introduction Rainbow trout (Oncorhynchus mykiss), which is classified as salmonids, is one of the world’s most important aquaculture species and is farmed in many countries (Esmaeili et al., 2017). Due to the increasing demand for rainbow trout, Chinese researchers are establishing mariculture system using deep-sea cages far offshore in the Yellow Sea Cold Water Mass of China (Evans, 2018; Dong, 2019). The ‘mountain-sea transfer’ culturing method is used, in which juvenile fish are hatched and cultivated in freshwater in mountainous areas before being transferred to seawater cages for growth until harvest. The parr-smolt transformation process of sa
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