The non-significant effect of increasing dietary lipid levels from 6 to 14% on weight gain, feed intake and survival was expected because our test diets were isonitrogenous and isocaloric and contained essential nutrients at levels that meet or exceed the know requirements for tilapia.
A number of earlier studies have reported similar weight gain and FER of channel catfish, Ictalurus punctatus, blue tilapia (O. aureus) and European sea bass (Dicentrarchus labrex) fed diets supplemented with increasing levels of fish oil. The non-significant effect of dietary fish oil levels on feed intake has also been reported for channel catfish.
However, significantly lower FER in fish fed diets supplemented with 14% lipid, regardless of dietary levels of vitamin E,
may be due to excessive levels of dietary lipid.
Lim and Webster reported that tilapia do not tolerate as high a dietary lipid as do salmonids.
A dietary lipid level in excess of 12% depressed growth of juvenile O. aureus×O. niloticus hybrids.
Thus, for good FER, lipid levels in diets of Nile tilapia juveniles should not exceed 10%.