Comparison of gut fluorescence and gut dry mass techniques for determining feeding periodicity in lotic mayflies

Abstract

AbstractGut tube dissection and gut fluorometry are methods that allow assessment of mayfly gut contents for the determination of diel feeding periodicity. We conducted laboratory experiments that quantitatively compared the field applicability of the 2 methods. Our study demonstrated that larval mayflies could be frozen for up to 6 mo without affecting the levels of chlorophyll a extracted from their guts. The ability to freeze mayflies and the possibility of working with reasonably small numbers of larvae, negligible background chlorophyll a levels, and flexible extraction times gives gut fluorescence comparable flexibility to preserving mayflies for the dry mass technique. Direct comparisons of the 2 gut content techniques revealed similar gut evacuation rates of Baetis larvae fed an ad libitum supply of Navicula. The maximum time between samples for either technique should be ≤4–8 h to estimate diel feeding periodicity accurately. Fluorometry and dry mass techniques were equally suitable to field stud...