International Journal of Marine Science 2016, Vol.6, No.34, 1-7
5
Table 2 Mean values of water parameters monitored during the 4 weeks culture period.
Parameters
Garlic-containing diets
(% / kg diet)
0
1
2
3
Temperature (
0
C)
27.35
27.05
27.30
27.32
pH
7.38
7.20
7.25
7.27
Dissolved oxygen (mg/l)
4.72
4.42
4.34
4.15
Discussion
The significant (P < 0.05) FW and MWG recorded in the fish group fed on the GP at 3% graded level in this study
is contrary to the opinions of Irkin et al., (2014) who reported that the efficacy of different doses, particularly at
high doses, appeared to be worse based on investigations of toxicology. Similarly, Yilmaz and Ergun (2012)
reported that high concentrations of phyto-additives may result in negative effects on fish health which is also
contrary to the data generated in this study in which high survival rates was recorded at the end of this experiment.
These may explain the fact that allicin, the major bioactive compounds in garlic, which enhances growth response,
stimulate appetite, improve anti-oxidant status and act as immune-stimulants and anti-stress in fish may cause
different synergetic effects on different finfish species. Results in Table 1 are in agreement with that reported by
Soltan and El-Laithy (2008) who reported that the incorporation of garlic in diets for growing Nile tilapia
significantly improved MWG and SGR.
The survival rate was significantly greater in all garlic-supplemented groups (1% - 3% graded levels of GP) when
compared with the control group (0% graded level) at the end of the experiment. However, the survival rate was
significantly higher in the group fed GP at 3% graded level. Although the use of garlic resulted in good survival
rates, feeding the higher doses of garlic for extended periods gave better results (Figure 3). The current results
showed the stimulatory effect of garlic on the immune system that correlates with improved fry survival. In
general, the significant (P < 0.05) growth rates recorded in the group fed
A. sativum
when compared to the control
group fed the basal diet in this present study could be attributed to the fact that the various organosulphur
compounds, including allicin in garlic enhance various activities such as growth, appetite, and also play pivotal
role as immunostimulant and antistress.
There is a paucity of information on the optimum dosage and duration regime of garlic as growth promoters in
different finfish species and with more emphasis on the red belly tilapia,
T. zillii
. For instance, Shalaby et al. (2006)
reported a significant increase in MWG, FER, PER, and SGR of Nile tilapia fed diet containing 3% GP. Similarly,
Diab et al. (2002) mentioned feeding diet with 2.5% garlic resulted in the highest growth performance in
O.
niloticus
. In the same species, Abou-Zeid (2002) found a positive improvement in biomass and SGR with garlic
supplementation. Metwally (2009) also mentioned that the best performance was obtained in Nile tilapia fed diet
with 3.2% GP. On the other hand, Mehrim et al. (2014) conducted a study on the dietary addition of garlic lobes in
O. niloticus
at 0, 1, 2, and 3% inclusion levels for 60 day regime and they observed significant growth in
O.
niloticus
at 1% / kg diet which is a growth pattern different from those obtained in
T. zillii
in this present study.
The different growth pattern in the
O. niloticus
recorded by Mehrim et al. (2014) for 60 d regime and those
recorded in
T
.
zillii
in this present study for 28 d regime could be due to differences in fish species to metabolize
the active bioavailable dose in the garlic-containing diets. According to Pollack et al. (2003), differences in the
growth response to a phytochemical may be due to differences in fish species’ ability to metabolize or utilize a
particular substance to which it has been exposed in the diet. The significant (P < 0.05) growth responses and feed
utilization recorded in
T. zillii
fed the highest dose of 3% graded level of
A. sativum
is contrary to reports of Mehrim
et al. (2014) who recorded significant growth in
O. niloticus
fed
A. sativum
at 1% graded level and least significant
growth at 3% graded level. This may explain the variable effects of phytochemicals on certain endpoints in different
species and differential levels of growth performance by a particular fish species at various concentrations of the
phytochemical (Chakraborty et al., 2013). Further research to analyze the functional mechanism behind the
physiological activity of garlic-supplemented diets in different finfish species needs to be investigated.
