摘要：Aquaculture is the only agricultural sector demonstrating constant economic growth within the past decade. Nowadays trend is to produce drug free products, which requires the use of animals with strong irmnune response to pathogens. The present study, investigates the seasonal variations of natural immunity among three of the most corn- mon fish in Bulgaria - Rainbow trout, Common carp and Russian sturgeon. The diverse phylogenet- ic development of each of them, leads to establish- ment of different defense strategies and prioritiza- tion of immune system components. The focus of this experiment were the levels of blood serum lysozyme, the two major pathways of complement. activation (classical and alternative — CPCA and APCA, respectively) and some of the acute phase proteins (ceruloplasmin and albumin). Expectedly, the highest lysozyme and ceruloplasrnin levels for both seasons was observed among the Russian sturgeon. Surprisingly, the sturgeon showed the highest: CPCA activity as well, whereas its APCA results were rather modest. Despite the divergent temperature preferences of the other two species, they both exhibited an increase in all parameters of interest in summer to winter direction. Exception of this rule was detected for the lysozyrne and albumin levels among the cormnon carp, where the opposite tendency was unveiled. The obtained data should give a new insight to fish growing programs fo- cused on the specific immune system features of each species.
