Variations in the content of trypsin and trypsinogen in larval herring (Clupea harengus) digesting copepod nauplii

Trypsin and its proform trypsinogen were quantified by radioimmunoassay in herring (Clupea harengus ) larvae subjected to different prey densities. During the first weeks of larval life, the enzyme content fluctuated in a three-phased pattern. Yolk resorption (Phase 1) was characterized by an increase in enzyme. During the first few days after yolk resorption (Phase 2), there was a sharp decline in enzyme. Older larvae (Phase 3) exhibited a second period of intensive enzyme synthesis. At first feeding, a basal level of gut enzyme of similar to 30 ng was recorded, and the amount of additional enzyme secreted from the pancreatic tissue into the intestine appeared to be dependent upon the numbers of prey items ingested. The enzyme-substrate ratio in the intestine was similar to 1 to 4. Prey availability affected amount of trypsinogen. Larvae experiencing a high prey density had an approximately two-fold higher specific enzyme content in Phase 2 compared to larvae exposed to a low prey density. A proposed nutritional strategy for first feeding herring larvae is discussed.