Jacques Gabaudan

Influence of dietary glucan and vitamin C on non-specific and specific immune responses of rainbow trout (Oncorhynchus mykiss)

Abstract A trial was conducted to determine the effect of a combination of dietary glucan and vitamin C on the immune response of rainbow trout. After 3 weeks of adaptation on a control diet (without glucan but containing 150 ppm vitamin C), rainbow trout were fed the experimental diets containing yeast glucan and vitamin C at 150, 1000 and 4000 ppm for 2 weeks and then switched back to the control diet for the following 4 weeks. Macrophage activity (chemiluminescence response), complement activation and lysozyme levels were monitored just after feeding the experimental diets (week 0) and 2 and 4 weeks later. The kinetics of antibody response after vaccination against enteric redmouth disease were determined. The fish were immunised at week 0, at the end of the experimental feeding. Tissue ascorbic acid contents were monitored every 2 weeks and reflected the dietary treatments. No differences were observed in complement levels activated via the classical pathway. Two weeks after feeding the experimental diets, alternative pathway of complement activation and chemiluminescence response were enhanced by high doses of vitamin C. Significant enhancement of macrophage activity was still evident at week 2. No significant differences were observed in lysozyme levels. The specific immune antibody response was enhanced following vaccination, when glucan was also present in the diet.

Influence of dietary vitamin C on the wound healing process in rainbow trout (Oncorhynchus mykiss)

This study evaluated the influence of dietary vitamin C as ascorbyl-phosphate on the healing process of experimentally wounded rainbow trout, in order to establish recommendations for salmonid feeding with regard to a reduction of the impact of winter sores. Three duplicate treatment groups of fish (mean initial body weight 56 g) were fed experimental diets containing 20, 150 and 1000 mg ascorbic acid (AA) equivalents/kg feed, respectively, for 4 weeks. Fish were then experimentally wounded, and sampled at 0, 3, 7, 10 and 21 days post-wounding for histological examination (skin and muscle), and AA concentration (skin, muscle, blood plasma, liver and head kidney). Experimental diets were continued during the sampling period. Comparison of the dietary treatments was based on the evaluation of a broad range of 22 histological indices and on the measured AA concentrations. Results showed that skin and muscle AA concentrations analysed at the level of the wound were correlated with dietary intake. Of the 22 histological indices evaluated, 13 exhibited significant differences between the three dietary treatment groups. These indices on which dietary vitamin C intake had the greatest affect were generally those containing fibrous tissue, including the repair of damaged dermal fibres, re-vascularisation and the re-establishment of normal dermal and muscle structure. Of the 13 indices, 7 also showed differences between the 150 and 1000 mg AA/kg feed groups at some point during the healing process. A large majority (11) of the 13 significant indices showed a more rapid healing process in the higher two dietary AA treatments, whereas only three showed a faster initial onset of response. Conclusions: (1) dietary vitamin C intake influences the rate of wound healing in rainbow trout, (2) increasing the dietary level of vitamin C from 150 to 1000 mg AA/kg feed enables the establishment of larger pools of AA in various tissues, and (3) with larger tissue AA pools, the increased AA demand following wounding does not become a rate limiting step, thus healing may proceed more quickly.