Hello,

I think it decreases. Also, read the following article, which seems very useful in your case:

http://www.sciencedirect.com/science/article/pii/0300962995000437

Thanks  Mr. Hoseini.

Greetings

See the following article downloaded.

Abstract I sent to you.

good luck

Protein nutrition and defence mechanisms in rainbow trout Oncorhynchus mykiss

Viswanath Kiron, Takeshi Watanabe, Hideo Fukuda, Nobuaki Okamoto, Toshio Takeuchi

• Abstract

The modulation of non-specific and specific immune mechanism by dietary protein was examined in rainbow trout. The lysozyme activity was reduced in protein-deficient fish. The variation of C-reactive protein level in fish at different nutritional statuses merits further examination. Antibody production was maintained, even in protein-deficient fish, indicating that defence systems operate preferentially to ward off infection. Pathogenic challenge trials reveal the importance of an optimum level of dietary protein, from the point of health; resistance to viruses varied among the different strains of trout.

Thanks, Dear Mohsen

It is changes according to the protein resources, and ratio of feed, feed additives, feed production methods,  feed storage media etc...