Background

Sea-lice infestation is an escalating problem for the salmon farming industry. Sea lice create entrance routes for bacterial and viral infections normally arrested by undamaged skin, and lice infestation is notably troublesome for the fish. The overall result is impaired general performance, higher mortality, reduced growth and lower quality of slaughtered fish. Annual losses related directly to sea-lice infestations in Norwegian salmon farms, amounts to more than a billion NOK. In addition, the sea-lice problem in salmon farms is a threat to wild salmon. The study reported in this brief note, has shown that when immunity in skin and mucous of salmon becomes enhanced by MacroGard®, in feed, their resistance sea-lice is also enhanced. This discovery points to an environmentally friendly alternative to anti-parasitic chemicals in the fight against sea-lice in salmon farming.

Experiment

Totally 450 Atlantic salmon (Salmo salar L.), average start weight of 680 grams, were distributed in 9 cages (5x5x5 metre) with 50 fish in each. Sea-water temperature was on average 15.30C (12.3 – 17.4 0C) during the experimental period of 70 days (weeks 25-36, 2006). The fish were fed a diet with same energy and protein content as in the most used growth feeds. The 9 cages were divided in the following 3 experimental groups (3 cages in each):

Group 1: Control diet (Control)

Group 2: Control diet + 2000 ppm PatoGard™

Group 3: Control diet + 1000 ppm MacroGard®

The fish were ”over-fed” (+15 % according to table) and excess feed registered. Sea-lice infestation occurred naturally in the sea farm where the experiment was carried out, at Averøy in Norway (AKVAFORSK), 2006

Results

In Group 3 (+ MacroGard®) there were 56 % lice-free fish at the end of experiment, in Group 1 (control) 39 %, and in Group 2 (+ PatoGard™) 32 %. The difference between the MacroGard®-group and the two other groups was statistically significant (Duncan’s multiple range test p< 0,05), whereas the difference between groups 1 and 2 was not.

Comments

The natural defence against skin parasites, including sea-lice, consists of enzymes, immunoglobulines, complement factors and other substances produced by immune cells inside the body and secreted into mucous and the outer skin surface layers. The ability of fish to avoid parasitic skin infestations is therefore highly dependent on their immune status and effective mucous immune mechanisms. A comprehensive amount of documentation exists on how MacroGard® stimulates immune defence mechanisms and that feeding of MacroGard® results in higher production and secretion into skin and mucous of immune products that protect against virus and bacterial infections. And - since these immune mechanisms are involved also in the defence against parasites – sea-lice- it was not a surprise that MacroGard® protects also against sea-lice infestation.

MacroGard® is a beta-1,3/1,6-glucan found as a structural element in the cell wall of yeast, and which has been released from the cell wall complex in a technological process which removes most other components. PatoGard™ is another yeast cell wall preparation, but in this preparation the immune stimulating beta-1,3/1,6-glucan has not been released and exposed during the extraction process. Like other crude yeast cell preparations (on the market), PatoGard™ has therefore no or very low immune stimulating effect, and as shown in the present experiment, no effect on sea-lice neither. However, being rich in mannose containing proteins, PatoGard™ may protect against bacterial gut infections by interfering with the binding of pathogenic bacteria to their receptors in the gut mucosa. Product: MacroGard® Feed Ingredient Version: 2007 Page: 3 of 3 ©Immunocorp Animal Health AS, 2007 Phone. +47 23 11 34 70 sales@immuncorp.no Arbins gate. 4, N-0253 Oslo, Fax: +47 23 11 34 71 Norway

PatoGard™ has also other beneficial effects which point the way to a next generation health feed for fish – used in combination with MacroGard®.

The study has demonstrated that it is possible to reduce the sea-lice problem in salmon farms by feeding MacroGard® to the fish.