12 months. Some symptoms such as the lack of
equilibrium during swimming and the loss of direction
were observed. The authors reported that the
Al+3 taken up by tilapia were not accumulated in
the body and subsequently excreted in the faeces.
The high concentrations of Al in faeces indicate
low absorption by tilapia organs.
The largest hepatocytes and the highest lipid
content were observed in fish fed Alga100 diet
(Fig. 6). Similarly, lipid droplets in hepatocytes
were observed in carp fry when fed mustard oil
cake (Hasan, Macintosh & Jauncey 1997). The
authors explained that the lipid changes in the
liver were probably a result of the presence of toxins
in the feed which caused disturbances in fat
metabolism. Morphology of the digestive tract indicated
that feeding algae-enriched diets did not
adversely affect the digestive system functions in
Nile tilapia (Figs 6–8).
In conclusion, our findings suggest that algae
meal protein can replace up to 50% of corn gluten
protein in the diets for juvenile Nile tilapia
without adverse growth effects. Higher inclusion
of algae meal protein resulted in significantly
decreased growth performance of juvenile tilapia,
probably affected by the increased Fe and/or Al
availability. Further research is still necessary to
eliminate Al and Fe negative effects on dietary
availabilities of phosphorous supplements. Also, to
examine other positive aspects of algae supplementation
such as attractants being used
(increased consumption), enrichment in carotenoids
(colouration) and enhanced immunity
enhance.