Effect of dietary fish meal replacement by red algae, Gracilaria arcuata, on growth performance and body composition of Nile tilapia Oreochromis niloticus
Younis, El-Sayed M. . 2018
A 12-week long feeding experiment was initiated to evaluate the effect of dietary supplementation of red
algae, Gracilaria arcuata, on the growth performance, feed utilization and body composition of Nile tilapia
Oreochromis niloticus (Linnaeus, 1758). The fish were fed with an algae-free control diet (C) and three
experimental diets which replaced conventional fish meal with varying levels of dried G. arcuata (20%,
40% and 60%, represented as G20, G40 and G60, respectively). The growth parameters of final weight
(FW), weight gain (WG), percentage of weight gain (WG%), daily growth rate (DGR) and specific growth
rate (SGR) were significantly reduced (P < 0.05) at all levels of algae incorporation compared to the control
diet. Moreover, the negative impact of Gracilaria meal on the growth performance of Nile tilapia
increased as the proportion of algae in the diet increased, with fish on diet G20 exhibiting a significantly
higher growth performance than the fish on either of the G40 and G60 diets. On the other hand, the feed
utilization parameters feed conversion ratio (FCR) and protein efficiency ratio (PER) did not show significant
differences between the fish in the control group and those on diet G20, although poorer FCR and
PER outcomes were achieved in the case of fish on diet G60. The content of moisture, protein and ash in
muscle and carcass increased as the proportion of Gracilaria meal in the diets increased, but the reverse
was true for lipid level. These results indicate that incorporation of less than 20% red algae, Gracilaria
arcuata, could be feasible in the diet of Nile tilapia and further studies are recommended to optimize
the level of algae to improve growth performance
Nile tilapia (Oreochromis niloticus) weighing 51.66 ± 2.42 g were exposed to 0%, 20%, 40%, and 60% of LC50 to either lead nitrate (Pb(NO3 )2 ) or copper sulfate (CuSO4 ) for 30 days.
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