International Journal of Aquaculture, 2015, Vol.5, No.22 1
-
7
2
for Chinook salmon (
Oreochromis tshaytscha
) (Martin
and Wertheimer 1989), African catfish (
Clarias gariepinus
)
(Haylor, 1991) and Arctic charr (
Salvelinus
alpinus
)
(Jrensen et al., 1993). In tilapia, experiments on the
effect of stocking density have been conducted on
different fish sizes including fry and juveniles
(El-Sayed, 2002), sub-adults (D’Silva and Maughan,
1995) and large tilapia (Yi et al., 1996). Studies were
also conducted using different culture systems such as
tanks (Bailey et al., 2000), ponds (Diana et al., 2004)
and net cages (Cruz and Ridha1996; Yi et al., 1996;
and Ouattara et al., 2003). All these studies showed
the direct relation of stocking density and growth
performance. However, some studies carried out by
(Siddiqui et al
.
, 1989) and (Watanabe et al., 1990) showed
the absence of the direct relation of stocking density. It
is evident, therefore, that further studies are needed to
verify the effects of stocking density on the growth
performance of
O. niloticus
in cage practice.
The major objective of this study was to determine the
relationship between stocking density and the production
of Nile tilapia in cages. Other related objectives were to
determine the effect of stocking density on growth,
mortality rate and finally the feasibility of Nile tilapia as
a species suitable for cage culture in Egypt.
Materials and Methods
Location and experimental design
The study was carried out in 2012 in El-Bagouria
canal at El-Hamoul Minufiya . The rectangular cages
measured 1x1x1.5 m and were made of black
polyethylene netting of 5-mm mesh size, square
measure. The submerged volume of each cage was 1 m
3
.
Cage frames were made of split bamboo. The cages
were suspended from a bamboo structure fixed by
cotton-nylon cords to a walkway from shore. Plastic
bottles, attached along the four sides of each cage,
were used as floats.
The experiment was a completely randomized design.
There were four stocking densities and there were
three replicates of each treatment. Twelve cages were
used in the experiment. Nile tilapia fingerlings were
obtained from the private fish farm at 96 tolompate 7,
Kafr El-Sheikh governorate, Egypt. Fish were treated
with a solution of phormaline (100 ppm) for 2-3 min
before being placed in cages at the experimental site.
A total of 975 fish were stocked on May 1, 2012 at
30.2 g average weight per individual fish at four
different densities (25, 50, 100, and 150 fish /m
3
and
harvested 196 days later on November 10, 2012.
Food and feeding
.
Nile tilapia least cost diet pellets of two sizes
(El-Saidy and Gaber, 2002) was formulated. The diet
contained 53.5 % SBM, 1.0 % L-methionine and
0.5 % L- lysine (Table 1). Amino acid composition of
the diet was calculated from tabular values provided
for diet ingredients (NRC, 1993) and was containing
the requirements of amino acids for Nile tilapia. Diet
was formulated to be 30.2 % crude protein and 4.8
kcal gross energy per g of diet.
Table 1 Composition and proximate analyses of the diet used in
the study
Ingredients (%)
Diet
Soybean meal (44%CP)
53.5
Wheat mediling
18.0
Yellow corn meal
18.0
Soybean oil
5.0
Vitamins & minerals primix
1
1.0
Calsum di-phosphate
1.0
Mollases
2.0
L-methionine
1.0
L-lysine HCl
0.5
Proximate analysis (%)
Dry matter
94.6
Crude protein
30.2
Crude fat
12.5
Crude ash
6.6
Crude fiber
3.8
Nitrogen free extract, NFE
41.5
Gross energy, GE
2
(kcal/ g diet)
4.8
1
Vitamins and minerals premix supplied the following vitamins
and minerals (mg or 1U) kg of diet: vit. A, 8,000 I.U.; vit. D,,
4,000I.U.; vit. E, 50 I.U.; vit. K3, 19 LU.; vit. B2. 25 mg; vit.
B3, 69 mg; Nicotinic acid, 125 mg; Thiamin, 10 mg; Folic acid,
7 mg; Biotin, 7 mg; vit. B, 75 mg; Cholin, 400 mg; vit. C, 200
mg; Manganese, 350 mg; Zinc, 325 mg; Iron, 30 mg; Iodine,
0.4 mg; Cobalt 2 mg; Copper, 7 mg; Selenium, 0.7 mg; and 0.7
mg B.H.T. according to Love11 (1989).
2
GE (Gross energy) was calculated according to NRC (1993)
by using factors of 5.65, 9.45 and 4.22 Kcal per gram of protein,
lipid and carbohydrate, respectively
In preparing the diet, dry ingredients were first ground
to a small particle size. Ingredients were thoroughly
mixed and then thoroughly added water to obtain a
