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International Journal of Aquaculture, 2014, Vol.4, No.08
http://ija.sophiapublisher.com
52
Nigeria. The water level in each tank was maintained
at a depth of 0.45 m throughout the experiment and
replaced every three days to maintain relatively
uniform physico-chemical parameters and prevent
fouling from feed residues. The source of water was
from Federal University of Technology, Akure water
station. Each tank was well aerated using air stones
and aerator pumps (Cosmos aquarium air pump,
double type 3500 50Hz, 2.5w-3w) as described by
Lawson (1995). The dissolved oxygen content and pH
of the water were measured using dissolved oxygen
meter (Jenway 3015 pH meter, 0.0 accuracy; Genway,
Staffordshire, UK) after standardizing the meter and
water temperature by a bulb thermometer (Paragon
Scientific Ltd, Birkenhead, Wirral, UK).
4.2 Experimental procedure & feeding trials
There were six dietary treatments each having two
replicates, with 15 fish each with a mean initial body
weight and standard length of 6.23 ± 0.1g. The fish
were weighed, distributed into experimental tanks and
allowed to acclimatize for 14 days before the
experiment. The experiment lasted for 8 weeks during
which the fish were fed at 5% body weight twice daily.
The diet per day was divided into two; 2.5% given in the
morning by 8.00 – 9.00 am and 2.5% in the evening by
5.00 pm. Weight changes were recorded weekly and
feeding rates adjusted to the new body weights.
4.3 Treatment of soybeans and diet formulation
Soybean (
Glycine max
) bought from a market in
Akure, Ondo State was processed by using heat
treatment method. The soybean was weighed using
electronic weighing balance and toasted for 10 hours
at 70
℃
and ground into fine powder to form a meal.
5.1 kg soybeans meal was mixed with 5.1 litres of
water and dried in an electronic electric oven at the
rate of 70
℃
for 8 hours. After incubation dried meal
was blended again into fine powder packed in plastic
bags and stored at ambient temperature prior to use.
Ingredients were mixed together at the right
proportion to formulate 30% crude protein diet. Then
phytase (enzymes) were added into each mixture at 0,
2000, 4000, 6000, 8000, and 10000 units phytase/kg
diet. Each diet mixture was treated separately and
extruded through a ¼ mm die mincer of Hobart A-200T
pelleting machine (Hobart GmbH, Rben-Bosch,
Offenbug, Germany) to form noodle-like strands, which
were mechanically broken into suitable sizes for the
O.
niloticus
fingerlings. The pellets were sun-dried, packed
in labelled polythene bags and stored in a cool dry place
to prevent fungal growth (Table 5).
Table 5 Gross composition of experimental diets
DIET1
DIET2
DIET3
DIET4
DIET5
DIET6
Fish meal
10.00
10.00
10.00
10.00
10.00
10.00
Soybean
44.50
44.50
44.50
44.50
44.50
44.50
Wheat
19.28
19.28
19.28
19.28
19.28
19.28
Maize
18.22
18.22
18.22
18.22
18.22
18.22
*Vit-min premix
2.00
2.00
2.00
2.00
2.00
2.00
Starch
1.00
1.00
1.00
1.00
1.00
1.00
Vegetable oil
5.00
5.00
5.00
5.00
5.00
5.00
Phytase (unit/kg diet)
-
2000
4000
6000
8000
10000
Total
100.00
100.00
100.00
100.00
100.00
100.00
Note: vit-min premix ( vitamin and minerals premix) each 2.5kg of premix contains; vitamin A, 12.5 million international unit (MIU);
D3,2.5 MIU; E, 40g; K3, 2g; B1, 3g; B2, 5.5g; B6, 5g; B12, 0.25g; Niacin 55g; Calcium pantothenate 11.5g; Choline chloride, 500g;
folic acid, 1g; Biolin, 0.08g; Manganese,120g; Iron,100g; Zinc,80g; Copper, 8.5g ; Iodine,1.5g ; Cobalt, 0.3g ; Selenium, 0.12g ;
Anti- oxidant,120g
4.4 Biological evaluation
Mean weight gain = [final mean weight (g) – initial
mean weight (g)]
Specific growth rate (SGR)=(LogW
f
–LogW
i
)×100/t (days)
Where, LogW
f
= logarithm of the fish final weight gain.
Log W
i
= logarithm of the fish initial weight, t =
experimental period in days
Feed conversion ratio (FCR) = Feed intake (g)/
Weight gain (g)
Gross feed conversion efficiency (GFCE) = 1 / FCR ×100
Protein efficiency ratio (PER) = Wet body weight gain (g)/
Crude protein fed