The gastric emptying time (G.E.T.) in turbot was investigated using X-radiography and was found to decrease with bemperature. Small fish processed a given ration, expressed as per cent body weight, faster than large fish (G.E.T. was found to be proportional to (fisheight)^'^^^). Large meals in a given fish were processed at a faster rate than small meals. Gastric emptying rate (G.E.R.) was found to be proportional to (meal size g)o.ela at 8" C and (meal size g)0'7ss at 19" C. These exponents are in agreement with a recently proposed model relating G.E.T. and G.E.R. to meal size (Fange & Grove, 1978). Large fish emptied a meal of given absolute size from the stomach at a faster rate (g h-I) than small fish. Experimental meals diluted with kaolin were evacuated in significantly less time than a control diet, suggesting that turbot may adjust feeding rates when food quality varies.

Gastric emptying time in Scophthalmus maximus, when fed friable artificial pellets based on fishmeal. is composed of two phases: (a) a delay time ( I d ) during which the meal forms a bolus and which shortens with temperature, and (b) an emptying phase (duration tend) which varies with meal size (8, body weight ( W ) and temperature (0 according to: log, tcnd=4.66+0.448 log, S-0.2664 log, W-0.051 7 (where tend is in h, S is in g, W is in g and Tis C). During the emptying phase, stomach contents decrease curvilinearly according to: S,O.448 = S00.448 -0.448 K (where S, & So is in g and I is in h) in which the instantaneous digestion rate, K , varies with fish weight and temperature as: ~= 0 . 0 2 1 ~0 . 2 6 6 4 p 5 1 iFood 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 a s 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-I). i s maintained at a lower level. Reduction in dietary energy density below I kCal g -' 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 YO respectively) irrespective of feeding rate and frequency.

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A series of experiments were carried out to construct an energy budget for juvenile thicklipped mullet, Crenimugil lahrosus Risso. A partial factorial experimental design was used to cxamine the effects of temperature, fish size and meal size on growth. The maximum ration that the fish were able to ingest completely per day was found to be 0.8, 1.4 and 2.3% wet body weight (R.w.) at 13,18 and 23" C, respectively. Ingested maintenance requirements (M.R.) were estimated to be 137, 205 and 288 cal fish-' day-' at 13, 18 and 23'C, respectively. At 18" C, M.R. varied as 25 W1J4 cal day-l, where W = fish weight (g). Growth rate increased with increasing temperature. Maximal conversion efficiency was 2 1-24% and was achieved closer to the maximum ingested ration with increasing temperature.The relationship between respiration rate and Wat 18' C for 3-20 g fish is described by: respiration rate (ml 0, h-I) = 0. I28 W 0.976 The energy cost of apparent specific dynamic action at 18' C was found to vary between 5.1% and 23.6% of the calorific value of the ingested meal (1% wet e . w . j , mean ( k S.E.)= 10.2 % 2'0%.Post mortem analyses of groups of fish fed 0.2, 0.8 and 1.5% wet B.W. meals showed a significant increase in total lipid and a significant decrease in water content with increasing ratio size. A negative correlation was found between body water content and total lipid (and calories).The mean assimilation efficiency (-+ S.E.) for 5-10 g mullet at 18' C was 73.9 f 3.6%.The observations reported in this study were brought together to construct an energy budget for juvenile C. lubrosus which was found to give a reliable prediction (within 10%) of energy demand and growth under the prevailing experimental conditions. Both gross (K,) and net (K2j, growth efficiencies, based on energy values, increased with increasing ratio size up to satiation and were independent of temperature. The maximum values of K , and K2 observed were 0.33 and 0.46, respectively. The third order efficiency (K,) appeared to be independent of temperature and ration size; mean values ranged between 0.66 and 0.84.

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