Differential digestion and evacuation rates of prey in a warm-temperate grouper, gag Mycteroperca microlepis (Goode & Bean)

Prey-specific gastric evacuation rates and digestion state indices were modelled for gag Mycteroperca microlepis, a large warm-temperate grouper, consuming meals of either baitfish (scaled sardine Harengula jaguana) or crab (purple swimmer crab Portunus gibbesii). Power exponential models best fit the wet and dry mass gastric evacuation data and the average digestion indices over post-prandial time (PPT), regardless of prey type or gag size (Adjusted R-2 >= 0.79). Gag mass (M) or total length (L-T) incorporated into an expanded power exponential model, along with exponential scalars, resulted in highly predictive (R-2 >= 0.87) gastric evacuation and average digestion state models. The expanded power exponential models fit to the baitfish and crab wet mass gastric evacuation data differed significantly (Kimura's likelihood ratio test (LRT), both P < 0.001). Gag consuming crab showed a digestive lag period of at least 4 h (wet mass) and took a longer time to complete digestion relative to gag consuming baitfish. Gag, as well as many other warm-temperate and tropical groupers, consume a mixture of fish and crab prey and they will therefore require the development of a consumption model that incorporates mixed-prey gastric evacuation models. (c) 2008 The Authors Journal compilation (c) 2008 The Fisheries Society of the British Isles.