Effect of yeast glucan on immunostimulation of cellular non-specific defences, growth and survival of arctic charr (Salvelinus alpinus L.)

Matolla, Geraldine Kasisi (1996) Effect of yeast glucan on immunostimulation of cellular non-specific defences, growth and survival of arctic charr (Salvelinus alpinus L.). Masters thesis, Memorial University of Newfoundland.

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Abstract

Arctic charr is a promising alternative aquaculture species in Atlantic Canada. Although one of the factors which limit the productivity of this species is microbial diseases, it has been given very little research attention. -- The use of vaccines and antibiotics are the two methods available for protecting farmed fish against microbial diseases. However, both methods suffer some drawbacks, leading researchers to search for alternative methods for controlling diseases. -- Immunostimulants, a group of biological and synthetic compounds, have been shown to increase non-specific activity in fish. The immunostimulatory effect of β-glucan from the yeast. Saccharomyces cerevisiae on non-specific defences, resistance to bacterial pathogen, Yersinia ruckeri infection, and growth in Arctic charr, were investigated. -- The effect on neutrophils and macrophages was monitored after treatment by injection with either 1 or 10 mg/kg and/or by immersion in 1 or 10mg/L of glucan suspension. Neutrophil activity was evaluated by their ability to stick to glass and staining by Nitro Blue Tetrazolium (NBT). Maximum neutrophil activation was observed 14 days after treatment by immersion in 1mg/L of glucan suspension. -- Phagocytic activity, which was assessed by Phagocytic Ratio (PR) and Phagocytic Index (PI), was determined by ingestion of heat treated yeast cells by head kidney macrophages from glucan treated fish. Both PR and PI were significantly elevated by immersion in 10mg/L between Days 2-14 as compared to Day 0 and Days 21-35 after treatment. -- Effect on disease resistance was monitored after infection of fish by intraperitoneal injection with Yersinia ruckeri. Glucan treated fish were challenged on Days 1, 7 or 14 following immersion in 1mg/L of glucan suspension. Treatment on 14 days prior to challenge resulted in higher survival than on Days 1 and 7. -- Maximum neutrophil and macrophage activation coincided with the day of maximum survival. This suggests that disease resistance in Arctic charr may be due to neutrophil and macrophage activation, which is stimulated by glucan treatment. -- Effect of glucan on the growth of the Arctic charr was also investigated in this study. However, glucan treatment of fish did not show any enhancement or reduction of growth. -- This study has demonstrated the potential of yeast glucan as a method for control of microbial diseases in Arctic charr.

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