In the present study, no significant differences were seen in
the growth and feed conversion ratios of fish fed diets containing
up to 12% fish oil, although weight gain and specific growth rate
were observed to decrease slightly as dietary fish oil increased.
Previous studies by Ng et al. (2001) with red hybrid tilapia showed
that high fish oil diets (10% cod liver oil) significantly reduced feed
efficiency when compared with diets containing 10% crude palm
oil. The same diet had no significant effects on growth, although
slightly reduced weight gains were observed. Similar overall observations
in the present study may indicate that the high levels of
fish oil, resulting in an imbalanced n-3/n-6 ratio, may have
exceeded the physiological tolerance of red hybrid tilapia for n-3
fatty acids. This may have resulted from competition between
n-3 and n-6 fatty acids for the same desaturase enzymes involved
in lipid metabolism