Gastric emptying and the return of appetite in juvenile turbot, Scophthalmus maximus L., fed on artificial diets

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Abstract
Gastric emptying time in Scophthalmus maximus, when fed friable artificial pellets based on fishmeal, is composed of two phases:(a) a delay time (td) during which the meal forms a bolus and which shortens with temperature, and(b) an emptying phase (duration tend) which varies with meal size (S), body weight (W) and temperature (71 according to: image (where tend is in h, S is in g, W is in g and T is °C). During the emptying phase, stomach contents decrease curvilinearly according to: image (where St, & So is in g and t is in h) in which the instantaneous digestion rate, K, varies with fish weight and temperature as: image Food pellets were prepared which remained separate and did not form a bolus in the stomach; K increased if a given meal size was subdivided to increase surface area. If meal size was increased by ingestion of identical pellets, K decreased. After a satiation meal, appetite in young turbot returns in direct relation to the degree of stomach emptiness. When food is regularly available, young turbot feed steadily at a rate which maintains their stomachs at c. 85% maximum fullness. When trained to use demand feeders, the fish interact as a group to feed rhythmically, but feeding rate falls 33% to only two‐thirds of the previous rate since stomach fullness, and hence digestion rate (g h−1), is maintained at a lower level. Reduction in dietary energy density below 1 kCal g−1 increases gastric emptying rate and the turbot demonstrate partial compensation by increasing food intake. On energy‐rich diets, protein nitrogen and energy assimilation efficiencies remain high (97 5% and 91% respectively) irrespective of feeding rate and frequency.