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Isonitrogenous and isocaloric diets containing 0, 18 or 36% toasted full-fat soybean meal (FFSM) were fed to Atlantic halibut. The diets were fed to five tanks of fish each for 34 days (period 1). Four tanks from each treatment were then retained in the growth experiment for a further 32 days (period 2), while the groups of fish from one tank from each of the 0 and 36% FFSM groups were split and transferred to two metabolism tanks each. The initial weight of the fish in the growth trial was 169 ± 1 g (mean ± SEM, n=12; weight range 89–253 g) and the final weight was 317 ± 5 g. There was no significant effect of dietary treatment on specific growth rate (range, 0.8–1.1% day−1), feed consumption (0.5–0.7% body weight day−1), feed efficiency (1.3–1.6 g wet gain g dry feed−1), protein retention (48–55%) or energy retention (49–57%). The fat, protein and energy concentrations in the fish increased during the trial and were not affected by the diet. The hepatosomatic index in fish fed with 36% FFSM diet was significantly lower (1.7%) than in the other groups (2.2%) (P

Apparent astaxanthin (3,3'-dihydroxy-beta,beta-carotene-4,4'-dione) digestibility coefficients (ADC) and carotenoid compositions of the muscle, liver, whole kidney and plasma were compared in Atlantic salmon (Salmo salar) and Atlantic halibut (Hippoglossus hippoglossus) fed a diet supplemented with 66 mg astaxanthin kg(-1) dry matter for 112 days. The astaxanthin source consisted of 75% all-E-, 3% 9Z- and 22% 13Z-astaxanthin, of (3R,3'R)-, (3R,3'S; meso)-, and (3S,3'S)-astaxanthin in a 1:2:1 ratio. The ADC of astaxanthin was significantly higher in Atlantic halibut than in Atlantic salmon after 56 and 112 days of feeding (P < 0.05). The ADC of all-E-astaxanthin was significantly higher than ADC of 9Z-astaxanthin (P < 0.05). Considerably more carotenoids were present in all plasma and tissue samples of salmon than in halibut. Retention of astaxanthin in salmon muscle was 3.9% in salmon and 0 in halibut. All-E-astaxanthin accumulated selectively in the muscle of salmon, and in plasma of salmon and halibut compared with diet. 13Z-astaxanthin accumulated selectively in liver and whole kidney of salmon and halibut, when compared with plasma. A reductive pathway for astaxanthin metabolism in halibut similar to that of salmon was shown by the presence of 3',4'-cis and trans glycolic isomers of idoxanthin (3,3',4'-trihydroxy-beta,beta-carotene-4'-one) in plasma, liver and whole kidney. In conclusion, the higher ADC of astaxanthin in halibut than Atlantic salmon may be explained by lower feed intake in halibut, and the lower retention of astaxanthin by a higher capacity to transform astaxanthin metabolically.

Four experimental diets were fed to triplicate groups of Atlantic halibut in a 2×2 factorial design, testing the effects of protein source and the use of an attractant. The diets contained 61% fish meal (FM) or 37% FM and 28% soy protein concentrate (SPC) with or without a coating of squid meal. In the SPC diets, 44% of nitrogen was supplied from the SPC. The mean initial fish weight was 633 g, and at the end of the 12-week trial, the mean fish weight was 874 g. There was no significant effect of dietary treatment on specific growth rate (0.43±0.02% body weight d−1, mean±S.E.M.). Feed efficiency ratio was significantly lower in the group fed the SPC diet (1.22±0.02) compared with those fed the FM diet (1.28±0.02). Fish fed the SPC diets had a higher feed intake (0.64±0.02%) than those fed the FM diet (0.59±0.02%). Addition of squid had no effect on feed intake. The groups fed diets not supplemented with squid were used for determination of whole body chemical composition, and the remaining fish from these groups were subsequently stripped for feces for digestibility estimations. There were no effects of protein source on digestibility or protein or energy retention in whole fish. The fish fed the diet containing soy protein had a slightly higher dry matter (DM) content (P

Seven-, 10- and 12-mm dry feed pellets were fed in excess in various combinations (A: 7 and 10 mm; B: 10 and 12 mm; C: 7, 10 and 12 mm) to triplicate groups of Atlantic halibut (Hippoglossus hippoglossus L.) in a 37-day trial. The fish, 1.8–3.1 kg, had been fed 7-mm pellets prior to the start of the trial. The fish were fed a meal every second day and waste feed was collected so that intake of each pellet size could be determined at each feeding. Specific growth rate (SGR), Feed effeciency ratio (FER) and intake in relation to biomass were calculated for each tank. A distinct preference for pellets of any one size was not seen, the different pellet sizes being eaten in approximately equal weights. Relative feed intake was significantly different among treatments and was highest in treatment C and lowest in B. The halibut on treatment B were slow to adapt to the absence of 7-mm pellets. SGR was approximately twice as high in the groups fed three pellets sizes in comparison with those fed two sizes (P