International Journal of Marine Science 2016, Vol.6, No.34, 1-7
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to the presence of various organosulphur compounds, including allicin (Augusti and Mathew 1974). Many reports
(Fo et al., 1990; Hu 1999; Aly et al., 2008; Aly and Mohamed 2010) have documented the effect of allicin as a
growth promoter.
Garlic (
A. sativum
) contains at least 33 sulfur compounds, several enzymes and the minerals germanium, calcium,
copper, iron, potassium, magnesium, selenium and zinc; vitamins A, B1 and C, fiber and water. It also contains 17
amino acids: lysine, histidine, arginine, aspartic acid, threonine, swine, glutamine, proline, glycine, alanine,
cysteine, valine, methionine, isoleucine, leucine, tryptophan and phenylalanine (Josling 2005). One of the most
biologically active compounds in garlic is allicin (diallyl thiosulfinate or diallyl disulfide). The most abundant
sulfur compound in garlic is alliin (S-allylcysteine sulfoxide), which is present at 10 and 30 mg g-1 in fresh and
dry garlic, respectively (Lawson 1998). Although allicin is considered the major antioxidant and scavenging
compound, recent studies show that other compounds may play stronger roles; such as polar compounds of
phenolic and steroidal origin, which offer various pharmacological properties without odor and are also heat stable
(Lanzotti 2006; Maniat et al., 2014).
Garlic inclusion in fish feeds has also been reported to increase growth performance in fish (Metwally, 2009).
According to Sheela and Augusti (1992) and Diab et al. (2002) garlic has the ability of enhancing catalase activity
in serum and lowering the levels of plasma glucose in fish. Dietary garlic as a growth promoter in Nile tilapia
(
Oreochromis niloticus
) improved body weight gain, feed intake and feed efficiency (Diab et al., 2002; Shalaby et
al., 2006). However, dietary garlic as a growth promoter coupled with the optimum graded level needed for the
growth, survival and nutrient utilization of red belly tilapia
Tilapia zillii
is yet to be well tested. On the other hand,
early sexual maturity of this species is a well-recognized problem. The problem of precocious sexual maturity and
unwanted reproduction has long been accepted as a major constraint to further development and expansion of
Tilapia culture (Ajiboye et al., 2015).There is a paucity of information on the optimum dosage and duration
regime of garlic as growth promoters in red belly tilapia
T. zillii.
Thus, the necessity for a laboratory experiment to
optimize the optimum graded level for the growth, nutrient utilization and survival of
T. zillii
reared in a glass
aquaria tanks for 28 days.
Methodology
This study was conducted under laboratory conditions at Aquaculture Department, Nigerian Institute for
Oceanography and Marine Research to optimize the optimum graded level for the growth, nutrient utilization and
survival of
T. zillii
reared in a glass aquaria tanks for 28 days. The experimental fish were acclimated under wet
laboratory conditions for two weeks and fed the basal diet. One hundred and eighty
Tilapia zillii
fry with average
body weight of 0.03 g were randomly stocked in each aquarium with average water holding capacity of 0.01m
3
and at a stocking density of 15 fish / glass aquarium, where three aquaria were referred to every dietary treatment.
Aquaria were daily cleaned, and the water exchange rate per day, including fish feces and remaining food, was
approximately 25% of the total volume. Then, each aquarium was refilled to a fixed volume also using stored and
well-aerated freshwater.
The bulbs of garlic were cleaned, peeled and cut into small pieces and dried in a Gallenkamp oven at 50°C for 14
hours at the Main Agriculture Laboratory of the Nigerian Stored Products Research Institute, Sapele out-station,
Delta State, Nigeria. The dried garlic (GP) was grinded in electric mill into fine particle size (< 200 μm), then
stored in a dry, air-tight transparent plastic container until composing of the experimental diets. GP was added in
experimental diet at levels 0, 1, 2 and 3% / kg diet. Fish were fed with test diet at a ratio of 3% of their body
weight for a period of 28 d, six days a week and twice daily at 0800 hour and 1600 hour. The present experiment
was designed as 4 treatments for 4 weeks factorial replicated thrice to assess the effect of dried garlic as growth
promoter in
Tilapia zillii
diet at levels 0, 1, 2 and 3% / kg diet. Estimation of experimental data on growth such as
weight gain (g), specific growth rate (SGR) was conducted. Survivability (%) test of fishes in each aquarium was
also conducted. Water quality parameters were regularly monitored throughout the experimental period for both
control and treatment aquarium using LaMotte test kit. Data generated from this study were analyzed by using
