Numerous studies have been conducted on the role of dietary lipid
sources and essential fatty acids on the immune response and disease
resistance in fish, but few studies have dealt with dietary lipid levels
and fish health. However, published information on the effect of
dietary lipid and essential fatty acids on immune response and disease
resistance in fish is inconsistent and often contradictory (Lim et al.,2008). In the present study, enhanced serum protein concentrations
were observed in fish fed 14% lipid diets. This increase in serum
protein could be due to elevated lipoprotein levels required for the
transport of excess lipid. Serum alternative complement, however,
significantly decreased in fish fed 10 or 14% lipid diets. Likewise,
Yildirim-Aksoy et al. (2009) obtained significantly increased serum
protein and decreased serum complement in channel catfish fed a
commercial diet containing 5.6% lipid supplemented with 6% or 9%
menhaden fish oil. They also reported increased lysozyme activity in
catfish fed diets supplemented with 3 or 6% fish oil. We found,
however, that dietary lipid levels had no influence on lysozyme
activity of Nile tilapia.