No abstract

The characteristic pink colour of salmonid¯esh is a result of deposition of naturally occurring carotenoid pigments. Achieving successful pigmentation in farmed salmonids is a vital aspect of ®sh farming and commercial feed production. Currently commercial diets for farmed salmonids contain either or both of the synthetic pigments commercially available, astaxanthin and canthaxanthin. Atlantic salmon, Salmo salar L. ( = 220 g initial weight) were given feeds where the pigment source was astaxanthin only, canthaxanthin only or a astaxanthin/ canthaxanthin mix. The rearing environment was 12 Q 3 m tanks supplied with sea water at the EWOS research farm Lùnningdal, near Bergen, Norway. As the proportion of dietary canthaxanthin increased,¯esh pigment levels also showed an increase; the pigment content in the muscle of canthaxanthin-only fed ®sh was 0.4 mg kg ±1 (or 14%) higher than that of the astaxanthin-only fed ®sh, with the mixed pigment fed ®sh being intermediate between the two extremes. Results of crosssection assessment for Minolta colorimeter redness (a*) values and Roche Salmofan TM scores also showed an increase in colour with increasing proportions of canthaxanthin in the feed. The data reported clearly indicates that S. salar ( = 810 g ®nal weight) of this size deposit canthaxanthin more ef®ciently than they do astaxanthin. These results contrast with those obtained by other authors with rainbow trout, Oncorynchus mykiss (Walbaum), and imply that the absorption or utilization of the pigments differs between species.

Atlantic salmon, Salmo salar, fitted with permanent dorsal aorta cannulae were fed diets containing either 0, 30, 60 mg kg−1 or combinations of astaxanthin and canthaxanthin, with the aim of comparing the uptake efficiencies to blood of the two pigments and evaluating possible interactions during absorption when formulated in the same diet. Given either astaxanthin or canthaxanthin in separate diets, at dietary levels of <30 mg kg−1, an identical linear relationship (R2 = 0.97) between dietary levels and blood concentrations was observed for both carotenoids. At dietary astaxanthin inclusions above 30 mg kg−1, blood astaxanthin concentration approached saturation at an average level of 1.2 ± 0.04 μg mL−1 (arithmetic mean ± SD), whereas blood levels of canthaxanthin continued to increase linearly throughout the inclusion range tested (0–60 mg kg−1). When both carotenoids were presented in the same diet, a reduction in the absorption efficiency of both pigments was observed (P < 0.05). This manifested itself as a lower level in blood than the level observed when each carotenoid was administered separately. The negative interaction was most prominent for astaxanthin, the maximum average blood saturation level of which fell (P < 0.05) to 0.73 ± 0.03 μg mL−1 (arithmetic mean ± SD). Our data support the conclusion that at higher dietary inclusions, canthaxanthin is more efficiently absorbed from the digestive tract into the blood of S. salar than astaxanthin.

No abstract

Cobia (8.4 ± 0.1 g body weight) were fed to satiation with three test diets of high plant protein‐based ingredients and different lysine to arginine ratios, and one commercial diet (currently used for cobia rearing in Vietnam as a control for growth) for 6 weeks. The test diets contained 206 g marine ingredients kg−1, including fishmeal, krill meal and fish protein concentrate (in order of high to low inclusion), while the rest of the dietary protein was a blend of soya and pea protein concentrate, wheat protein and sunflower meal. Crystalline lysine and arginine were added in the test diets to produce either a balanced lysine to arginine ratio (BL/A; 1.1) and a high or low lysine to arginine ratio (HL/A; 1.8 and LL/A; 0.8, respectively). There were no significant differences in final body weight, weight gain, feed conversion ratio or protein gain between cobia fed BL/A‐ and commercial control diet (CCT). Cobia fed BL/A diet performed better than fish fed either HL/A‐ or LL/A diet. This was partly due to a higher feed intake and protein and lipid gain in cobia fed BL/A diet as compared to HL/A‐ and LL/A diet.