Immunostimulant effects of nucleotide isolated from yeast RNA on carp, <i>Cyprinus carpio</i> L.

Nucleotides from yeast RNA were evaluated for their ability to enhance the non‐specific immune responses in carp, Cyprinus carpio . Oral administration of nucleotides to fish daily for 3 days resulted in enhanced responses of phagocytic and nitroblue tetrazolium (NBT) activities in kidney phagocytic cells. This activation of kidney cells was observed for at least 10 days post‐treatment. The serum complement and lysozyme activities also increased in fish treated with nucleotides. Furthermore, the number of Aeromonas hydrophila in nucleotide‐treated fish significantly decreased in the blood, kidney and liver after intraperitoneal injection. Thus yeast nucleotides appear to enhance non‐specific immune responses in fish.