The effect of Ulva pertusa meal supplementation on disease resistance was monitored by means of some pathological indices in red sea bream Pagrus major fed on a 5% Ulva meal sup-plemented purified diet.
The Ulva meal enhanced phagocytosis of the granulocytes against Pasreurella piscicida. In the fish immunized with formalin-killed P. piscicida, the blood lymphocyte number increased by feeding the Ulva meal, but the granulocyte number and agglutinin titer were not influenced.
Complement activities such as spontaneous hemolytic activity (SH₅₀) and bactericidal ac-tivity against Escherichia coli and P. piscicida tended to increase by the supplement.
Although the effect on prevention from artificial infection by P. piscicida was erratic, the Ulva meal supplementation was suggested to enhance disease resistance of the fish without impairment of growth. The importance of feeding algae was discussed on the basis of disease resistance.