The potential of the unicellular green algae ChI orella
vulgaris and Scenedesmus obliguus and the filamentous green
algae Cladophora glomerata and Hydrodictyon reticulatum
as protein sources in Oreochromis niloticus and Tilapia
zillii diets was investigated.
When Q. niloticus and !. zillii were fed with fresh
C. vulgaris and £. obliguus, a high percentage of the
ingested algae was found to be undigested. Heat treatment
of the algae at 40°, 60°, 80° and 100°C produced increased
growth and protein utilizations in the fishes compared to
those fed the untreated algae. Feeding Q. vulgaris treated
at 1000C for 30 minutes and S. obliguus treated at 1000C
for 15 minutes was found to have produced the best growth
responses in.Q. niloticus and!. zillii.
Q. glomerata meal and E. reticulatum meal were each
fed separately as fishmeal substitutes in pelleted rations
formulated to contain 30% protein with varying proportions
of this supplied by the fishmeal and the algal meal. A
diet containing 25% protein supplied by the algal meal
alone was also fed. When 5% of the fishmeal protein was
replaced with algal protein (both Q. glomerata and lie
reticulatum) and fed to !. zillii, the growth and protein
utilization values recorded were superior to those 'obtained
for the control 30% fishmeal protein diet. Higher levels
of algal protein substitution were, however, found to
produce poorer growth and protein utilization values in
both fish species. Diets containing only algal protein
(both Q. glomerata and H. reticulatum) produced the poorest
growth responses in both fish species.
Hydrodictyon reticulatum was found to be limiting in
methionine and histidine. Supplementation of these
essential amino acids produced improved growth in both
Q. niloticus and T. zillii.
It was concluded from these studies that the green
algae evaluated may be suitable partial dietary protein
sources for tilapias
