Digestibility of Three Fish Species by Double-Crested Cormorants

Abstract

I determined daily energy requirements of captive Double-crested Cormorants (Phalacrocorax auritus) and their metabolizable energy coefficients (MECs) for three fish species: channel catfish (Ictalurus punctatus), gizzard shad (Dorosoma cepedianum), and bluegill (Lepomis macrochirus). Ad libitum intake ranged from 264 to 503 g bird-1· day-1 among tests, resulting in metabolizable energy values of 616 to 1,334 kJ kg-1· day-1. Ninety percent of the marker carmine red was recovered in 48 hr, suggesting that collection periods should be ca. three days to determine digestion efficiencies. Estimated MECs ranged from 77.9% to 89.2% among fish diets, with bluegill < channel catfish = gizzard shad. No seasonal differences were found for MECs of catfish. Nitrogen corrections reduced MECs to approximately 75% for bluegill, 78% for gizzard shad, and 79% for channel catfish.