A laboratory study on digestive processes in the Antarctic krill, Euphausia superba , with special regard to chitinolytic enzymes

Abstract

Feeding experiments of 9, 14 and 20 days duration were carried out on the Antarctic krill, Euphausia superba. Two groups were fed with the chitinous diatom Cyclotella cryptica and the non-chitinous green algae Dunaliella bioculata, respectively. A control group remained unfed. The time courses of the activities of endo-and exochitinase in the stomach and the midgut gland were compared with those of the digestive enzymes protease, cellulase (1,4-b-D-glucanase) and laminarinase (1,3-b-D-glucanase). Speci®c activities of all enzymes were higher in the stomach than in the midgut gland. Characteristic time courses of activity were evident after 4 days. In starved animals, enzyme activities decreased to a minimum after 4 days and recovered within 14 days to initial values. In the stomach, the activities of endo-and exochitinase increased when krill were fed on Cyclotella. For animals fed with Dunaliella, activities stayed constant or decreased slightly. The results con®rm chitinases as digestive enzymes and, therefore, the capability of krill to utilize various food sources.

Seasonal differences in citrate synthase and digestive enzyme activity in larval and postlarval antarctic krill, Euphausia superba

“…Because of the complex digestive process, enzyme activity may vary between the two organs (Saborowski and Buchholz 1999). We found higher digestive enzyme activity in the stomach than in the midgut gland, a difference noted previously (Buchholz 1989;Saborowski and Buchholz 1999), probably reflecting a higher concentration of digestive juice. In either organs of adult krill the laminarinase and proteinase activity was higher in autumn than in summer.…”

“…These findings, like our own, are suggestive of an increase in enzyme concentrations at low food levels. In contrast, Saborowski and Buchholz (1999) showed that in starving E. superba, digestive enzyme activity rapidly decreases in the stomach and to a lesser extend also in the midgut gland. However, after advanced starvation of several days, activities recovered again but did not reach initial values.…”

“…Clarke and Walsh (1993) demonstrated that CS activity has the potential for defining the nutritional condition of copepods. However, nutritional condition depends also on the ability to utilise food efficiently, and sufficient activity levels of digestive enzymes are a prerequisite for processing this food, particularly under a variable food regime (Saborowski and Buchholz 1999).…”

Cysteine proteinases substitute for serine proteinases in the midgut glands of Crangon crangon and Crangon allmani (Decapoda: Caridea)

“…Total proteinase activity was determined by the hydrolysis of azocasein as described by GarciaCarreño (1992) and modified by Saborowski and Buchholz (1999). The reaction mixture contained 200 Al Tris-HCl (0.1 mold l À1 , pH 6.0, supplemented with 0.01 mold l À1 CaCl 2 ) and 20 Al of the midgut gland extract.…”

Tissue-specific distribution of pyruvate kinase isoforms improve the physiological plasticity of Northern krill, Meganyctiphanes norvegica

“…On starvation crustaceans reduce the size of the midgut gland and metabolize storage products such as lipids and glycogen (Strus, 1987;Papathanassiou and King, 1984). Furthermore, digestive enzyme activities decrease on starvation (Saborowski and Buchholz, 1999). The regulative potential of PKII in the midgut gland seems to be a suitable mechanism to control the glycolytic energy transfer.…”