International Journal of Aquaculture, 2015, Vol.5, No.3 1
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1.4 Feeding
Composition and proximate analysis of the practical
diet used in the present study are presented in Table 1.
The practical diet formulated to contain 33.8 % crude
protein and 4.5 kcal/g diet gross energy and covering
all nutrient requirements of Nile tilapia. In preparing
the diet, dry ingredients were first ground to a small
particle size (approximately 250µm) in a wiley mill.
Ingredients were thoroughly mixed and then
thoroughly added water to obtain a 40 % moisture
level. Diet was passed through a mincer with die into
2.5-mm diameter spaghetti-like strands and was dried
under sun for 8 h. After drying the diet was broken up
Table 1 Major ingredients and proximate analysis of the diet
fed to mono-sex Nile tilapia
O
.
niloticus
intensively reared in
concrete tanks at different stocking density and water exchange.
All values on a dry matter basis%
Ingredients (%)
Diet
Fish meal (60% C.P)
8.0
Soybean meal (44 % C.P.)
62.0
Wheat bran
8.0
Yellow corn meal
10.0
Soybean oil
5.0
Vitamins and minerals premix 1
1.5
Calcium di-basic phosphate
2.0
Molasses
2.0
L-methionine
1.0
L-lysine HCl
0.5
Proximate analysis2
Moisture
9.8
Crude protein
33.8
Crude fat
10.4
Ash
7.9
Crude fiber
6.7
NFE 3
31.4
Gross Energy (kcal/g diet) 4
4.5
Note: 1. Premix supplied the following vitamins and
minerals(mg or IU)/ kg of diet, vit. A, 8000 I.U.; vit. D3, 4000
I.U.; vit. E 50 I.U.; vit. K3, 19 I.U.; vit. B2, 25 mg; vit. B3, 69
mg; vit. B6, 20 mg; Nicotinic acid, 125 mg; Thiamin, 10 mg;
Folic acid, 7 mg; Biotin, 7 mg; Pantothenate, 15 mg; vit. B12,
75 mg; Choline, 900 mg; vit. C, 500 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 Xie, et al., (1997). 2. Values represent the mean of three
sample replicates. 3. Nitrogen free extract (NFE) = {100 -
(moisture + crude protein + crude fat + ash + crude fiber)} 4.
Gross energy was calculated using the gross energy values for
the macronutrients (5.6 kcal/g protein, 9.5 kcal/g fat and 4.1
kcal/g carbohydrate) according to Sanz, et al., (1994)
and sieved into appropriate pellet sizes. Diet was
stored at –20 C in plastic-lined bags until fish were
fed. The fish were fed with a daily quantity of food
equivalent to 5% of fish biomass in each tank during
the first 12 weeks, then gradually reduced to 2%
during the second 12 weeks, then reduced to 1.5 %
until the end of the experiment. Fish in each treatment
were fed manually their daily amount of food three
times daily at 0800, 1300 and 1600, six days per week
for 44 weeks. About 20% of fish in each tank were
randomly sampled and measured at 4 weeks intervals
for total length (L) (cm) and body weight (Wt) to the
nearest 0.1g.
1.5 Water quality analysis
Water temperature and dissolved oxygen were
measured every day using YSI model 58 oxygen
meter (Yellow Springs Instrument Company, Yellow
Springs, OH, USA). Total ammonia and nitrite were
measured once weekly using a DREL 2000
spectrophotometer (Hach Co., Loveland, CO). Total
alkalinity and chloride were monitored once a week
using the titration method, and pH was monitored
twice weekly using an electronic pH meter (pH pen,
Fisher Scientific, Cincinnati, OH). During the 44-week
rearing trial, the average water quality parameters (
SD)
were: water temperature, 26.9
1.2
℃
; dissolved oxygen,
5.4
0.6 mg l
-1
; total ammonia 0.2
0.1 mg l
-1
; nitrite,
0.04
0.03 mg l
-1
; total alkalinity, 185
47 mg l
-1
;
chlorides, 554
122 mg l
-1
; pH, 7.7
0.18.
1.6 Growth performance parameters
Growth response, production and feed utilization
parameters were calculated as follows: SGR (% day
-1
) =
100 (Ln final weight - Ln initial weight)/ days; Net
production = final biomass - initial biomass (kg/tank);
Gain in weight (g/fish)= mean final body weight - mean
initial body weight; Gain in total length = mean final
body total length -mean initial total length (cm/fish) ;
Condition factor (K) = 100(Wt/L
3
), where Wt is fish
body weight (g), L is total length (cm); Feed conversion
ratio (FCR) = total dry feed fed (g)/total wet weight
gain (g); Protein efficiency ratio (PER) = total wet
weight gain (g)/ total dry protein fed (g); Feed intake
(g/fish) was recorded daily and calculated at the end of
the experiment. Net income was determined by the
difference between the sale price of the fish after
harvest and the costs of fingerlings and food according
to Hengsawat, Ward & Jaruratjamorn (1997).
