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

Abstract

Gastric emptying time in Scophthalmus maximus , when fed friable artificial pellets based on fishmeal, is composed of two phases: (a) a delay time (t d ) during which the meal forms a bolus and which shortens with temperature, and (b) an emptying phase (duration t end ) which varies with meal size ( S ), body weight ( W ) and temperature (71 according to: image (where t end 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 S t , &amp; S o 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.