Fig. 1

Experimental trial setup. a Feed intake and lice challenge study. Atlantic salmon were fed control feed, low dose and high dose level of GLs for 21 days. The fish were then fed control feed for 10 days (acclimation), before continuing on the control, low dose and high dose feeds for 12 days (pre-infection period). The skin samples, weighing of the fish and lice counting from the three dietary groups challenged with L. salmonis (50 copepodites per fish) [infected fish fed control feed (I-C), infected fish fed low dose feed (I-LD) and infected fish fed high dose feed (I-HD)] were done after 31–35 days of infection (post-infection period). b Feed study. To study responses of the feed per se (without infection), Atlantic salmon were fed control feed and high dose feed. All fish were acclimatised with the same control feed for 30 days before the feed study commenced. Sampling of skin tissue and weighing of the fish from two groups [not-infected control group (NI-C) and not-infected high dose group (NI-HD)] were performed after 17–18 days of feeding experimental feeds