Digestive enzyme and gut surfactant activity of detritivorous gizzard shad(Dorosoma cepedianum)

Measuring digestive enzyme and surfactant activities tested specialization of gizzard shad (Dorosoma cepedianum) digestive physiology to a detritivoro us feeding strategy. Digestive enzyme activity was measured in adult and la rval gizzard shad using fluorescently labeled artificial substrates. Surfac tant activity in gizzard shad was measured by comparing gut juice drop diam eters over a range of dilutions. Enzyme activity in the ceca region of adul t gizzard shad was high for esterase, beta-glucosidase, lipase, and proteas e. Enzyme activity was lower in posterior intestine sections than in anteri or intestine sections, although protease activity remained high for the gre atest distance in the intestine. Micelles were detected in adult gizzard sh ad gut juice, and surfactant activity was greatest in the ceca region. Larv al gizzard shad protease activity was similar to that of adult fish, and su rfactants were below their critical micelle concentration. Gizzard shad cou pled digestive physiology with gut anatomy to obtain nutrients from detritu s, and these adaptations may explain elevated growth rates observed in thes e fish when they are planktivorous.