International Journal of Aquaculture, 2015, Vol.5, No.3 1
-
13
2
Stocking density is a major factor that affects on fish
growth under farmed conditions (Hengsawat et al.
1997; Maragoudaki et al
.
1999). Stocking density and
therefore, the volume of water per fish is a
significantly factor in determining production in
concrete tanks. Increasing stocking density results in
stress (Leatherland and Cho, 1985) which leads to
enhanced energy requirements causing reduced
growth and food utilization. Consequently, identifying
the optimum stocking density for a species may be a
critical factor is affecting growth and feed intake in
concrete tanks.
Studies have shown that aquaculture systems with
recycle water not only enabled water conversion but
also reduced pollution of receiving waters and
facilitated increased fish production when properly
designed and managed because of controlled
environment (El-Saidy et al., 2009). Little information
is available concerning the effects of stocking density
and water exchange rates under the concrete tanks
rearing system conditions.
The major objective of this study was to investigate
the effects of stocking density and water exchange
rates on growth performances, production traits, feed
utilization, body composition and finally the economic
feasibility of mono-sex male Nile tilapia (
Oreochromis
niloticus
) reared in concrete tanks recirculation systems.
1 Materials and Methods
This study was carried out at the out door installations
of the fish research laboratory, faculty of Agriculture,
Minufiya university, Egypt, in order to investigate the
effect of stocking density and water exchange rates on
growth performances, production traits and feed
utilization of mono-sex male Nile tilapia cultured in
concrete tanks.
1.1 Description of tank system used
The experimental system consisted of a series of
twelve concrete tanks; each of them was 2 m long,
2m-wide and 1.25-m height. Water level in the
concrete tanks was kept at one-meter depth to
maintain the water volume at 4 m
3
. The concrete tanks
were supplied with fresh water at a rate of 8 or 12 L/min.
The tanks were provided with continuous aeration
through an air compressor. The walls and bottoms of
the tanks were scraped and cleaned weekly. Also, all
tanks were drained and cleaned every 4 weeks during
sampling.
1.2 Experimental fish
A number of 4 males and 8 females (1:2) of Nile
tilapia, was stocked in concrete tank of 2 m long, 2m
wide and 1.25 m height. Supplied with fresh water
kept at 1 m depth, in the summer of 2003 the fries
were collected from the tank and transported to
another tank and fed on a diet containing 48.5 % crude
protein supplemented with 17-ά methyltestosterone
(Sigma company) at a rate of 60 mg/kg diet. Hormone
was dissolved in ethylalkhol and supplemented to the
diet and dried at 105 C in oven.
Fry was fed at a rate of 20 % of body weight daily for
28 days to obtain mono sex male. After that the fishes
were fed on a diet without hormone containing 47 %
crude protein (artificial food) at a rate of 10 % of body
weight daily in the second month, and then we fed on
a diet containing 33.8 % crude protein at a rate of 6%
of body weight daily. The daily amount of food was
divided into four times.
1.3 Stocking rates
A set of 3600 mono-sex Nile tilapia were of an
average initial weight of 7.5 (g) and average initial
length of 8.9 (cm/fish) were distributing in densities of
200, 300 and 400 fish per tank (4m
3
) to give a
stocking density of 50, 75 and 100 fish/ m
3
with
duplicate tanks per treatment for either 8L/min. or
12 L/min. water exchange rate as follows:
Treatments
Tank #
Water exchange rate
Stocking density (fish/tank 4m
3
)
1
1,2
8L/min.
200 (50fish/m
3
)
2
3,4
8L/min.
300 (75fish/m
3
)
3
5,6
8L/min
400 (100fish/m
3
)
4
7,8
12L/min.
200 (50fish/m
3
)
5
9,10
12L/min.
300 (75fish/m
3
)
6
11,12
12L/min.
400 (100fish/m
3
)
