Effects of Protein, Lipid, Feeding Levels and Their Interaction ... 79high VSI and IPF while the contrary occurred for the low lipid. It may be that
the fish fed with high lipid diets were unable to utilize all the lipid for energy
production and the excess fat was deposited in the viscera (Gallagher,1999).
Fattiness is often undesirable in fish cultured for food and increasing the
dietary protein level may be a strategy for producing a leaner product.
Hepatosomatic indices (HSI) were insignificantly higher in fish fed the
lower protein diets and there was a trends of gradually increased HSI with
increasing dietary lipid and energy, probably due to higher liver lipid and liver
glycogen accumulation as a result of lower dietary protein to energy ratios
(Brown et al., 1992; Nematipour et al., 1992; Jantrarotai et al., 1996, 1998;
McGoogan and Gatlin III, 1999). Generally, it appears that reducing feeding
level from 100 to 50% significantly reduced HSI, VSI and IPF. This could be
due to the difference in feed intake as those under satiation feeding have been
accumulating fat especially towards the end of the experiment while those
under low feeding might not have enough nutrients for their needs let alone
accumulation of fat.
CONCLUSION AND RECOMMENDATIONS
In this research, the best growth performances were observed in fish fed
with high protein with low lipid diet compared to others at the same feeding
level while the lowest growth performances were observed in those fed with
low protein and high lipid diet compared to other treatments at the same
feeding rate. At the same dietary protein and feeding level, fish growth
performances were better at low lipid than high lipid. From the results it is
likely that percent weight gain increases as the dietary crude protein and
feeding levels increase but decreases as the lipid level increases. Feed
efficiency was better at high crude protein and low feeding rate but not
significantly influenced by the dietary lipid level.
The use of low dietary protein level enhanced high plasma triglyceride,
cholesterol, and total protein. Low dietary protein level also enhanced high
HIS and IPF while high dietary lipid and feeding levels enhanced high
deposition of fat and viscerosomatic index in this experiment. Based on our
results, the study advocates for crude protein level between 25 and 35%, 8%
lipid level and feeding rate between 70 and 100% in a practical world. Further
research with O. niloticus should investigate fundamental aspects of the
physiology and biochemistry of dietary protein and energy utilisation. Well
known biochemical pathways provide the theoretical basis for this.