Introduction
Astaxanthin is an essential carotenoid in salmonid nutrition and a major determinant of flesh pigmentation, directly influencing consumer acceptance and market value. As salmonids are unable to synthesize astaxanthin de novo, dietary supplementation is mandatory. Beyond pigmentation, astaxanthin contributes to antioxidant protection, immune modulation, and stress resistance. However, its bioavailability is often limited by its lipophilic nature, low solubility in the intestinal environment, and reliance on passive absorption mechanisms. Nutritional strategies that enhance lipid digestion, emulsification, micelle formation, and postabsorptive transport may therefore improve astaxanthin utilization and retention. Lysophospholipids exhibit superior emulsifying properties compared to conventional phospholipids and are involved in lipoprotein metabolism. This study evaluated the effects of a lysophospholipidbased additive (Aqualyso, Adisseo) on growth performance and fillet pigmentation in Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss).
Material and Methods
Two feeding trials were conducted. In the first trial, Atlantic salmon post-smolts (initial body weight 160 g) were reared for 12 weeks in 1.2 m3 tanks (35 fish per tank; three replicates per treatment) under controlled salinity (33 ppt) and temperature (12 ± 2 °C). A basal diet (45% crude protein, 28% lipid) containing 60 ppm astaxanthin and no lecithin was supplemented with graded inclusion levels of liquid Aqualyso (0, 0.05, 0.1, and 0.2%). Fish were fed to apparent satiation. Growth performance parameters were assessed at weeks 6 and 12, and fillet samples were analysed for astaxanthin and total carotenoid concentration to determine pigment retention efficiency.
In the second trial, rainbow trout sub-adults (initial body weight 300 g) were fed for 10 weeks in a flow-through system (1,600 L tanks; 18 fish per tank; two replicates per treatment) at natural water temperatures (13–14 °C). A basal diet (44% crude protein, 25% lipid; 60 ppm astaxanthin) was compared with the same diet supplemented with 0.1% powdered Aqualyso. Growth performance was monitored, and fillet pigmentation was evaluated at weeks 5 and 10 using colourimetric analysis (CIE Lab* system; n=12 fillets per treatment at each sampling point). Statistical analyses were performed using one-way ANOVA or Students T-test, with significance set at p < 0.05.
Results
In Atlantic salmon, Aqualyso supplementation improved growth performance in a dose-responsive manner. The 0.1% inclusion level produced the strongest growth response, with numerically higher feed intake (+10%) and specific growth rate (+6%) compared to the control, observable from week 6 onwards, while feed conversion ratio was unaffected. All supplementation levels increased fillet astaxanthin concentration. The greatest improvement in pigment utilization was observed at 0.05% inclusion, resulting in a numerical increase of 32% in fillet astaxanthin concentration and a 29% increase in astaxanthin retention efficiency. Total carotenoid concentration and retention were numerically increased by 24% and 23%, respectively.
In rainbow trout, dietary inclusion of 0.1% Aqualyso numerically increased final body weight by 5% and improved feed conversion ratio by 3%. Colourimetric analysis indicated higher redness (a*) and yellowness (b*) values at week 5, and a significant improvement in hue angle (h) at week 10, indicating enhanced pigmentation efficiency compared to the control.
Discussion
Lysophospholipid supplementation improved growth performance and astaxanthin utilization in both salmonid species. These effects are likely linked to enhanced emulsification, more efficient micelle formation, improved lipid digestion, and increased intestinal absorption of lipophilic compounds such as astaxanthin. This pigmentation benefits were consistently demonstrated through complementary evaluation approaches: biochemical quantification of astaxanthin and carotenoid retention in Atlantic salmon, and objective colourimetric measurements in rainbow trout. Overall, the results support the use of lysophospholipids as an effective nutritional strategy to improve growth and optimize pigment efficiency in salmonid aquaculture.