C9 and infection: In the present study, a number of complement components including c3a.1, c3a.6, c4, c6, and c9 showed a reduced expression level in the congenitally asplenic zebrafish, indicating that the complement system was partially impaired. Defbl1 (also known as β-def-1) is a crucial antimicrobial peptide that plays an essential role in protecting the intestine against infection as a result of antibacterial and immunomodulatory properties (Cederlund et al., 2011).