Towards the standardization of brush border purification and intestinal alkaline phosphatase quantification in fish with notes on other digestive enzymes

Assessing the activity of digestive enzymes is a common procedure in many biological, physiological and nutritional studies. After reviewing the available literature on fish digestive tract maturation and enzymatic activity (pancreatic and intestinal enzymes) published between 1994 and 2017, authors detected some possible methodological and/or interpretative inconsistencies in this kind of studies, and concluded that special attention should be paid on: i) the time of conservation of frozen samples prior their analysis, ii) the proper purification of the brush border of enterocytes by a double centrifugation step (Crane et al., 1979) when authors want to evaluate the activity of intestinal brush border enzymes in order to avoid the overestimation, particularly of alkaline phosphatase (AP), because it is present in other tissues; iii) the use of the proper reaction conditions at the normal range of values in terms of ions, temperature and intestinal alkalinity for the species of interest, and AP unit calculation. The implementation of these recommendations will promote the standardization of actual analytical procedures, as well as improve the reliability of comparative studies between different fish species or rearing procedures.