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Effects of water exchange rate in intensive aquaculture system on fish productivity of desert concrete circulated ponds in egypt


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8th International Symposium on Tilapia in Aquaculture 2008


EFFECTS OF WATER EXCHANGE RATE IN INTENSIVE AQUACULTURE SYSTEM ON FISH PRODUCTIVITY OF DESERT CONCRETE CIRCULATED PONDS IN EGYPT
MOHAMED ALGAZZAR1, MOHAMED F. OSMAN2 AND SHERIF S. SADEK3


  1. General Manager in the General Authority for Fisheries Resources Development (GAFRD), E-mail m_elgazzar1@hotmail.com

  2. Fish Production Branch, Faculty of Agriculture, Ain Shams University, Cairo, Egypt .E-mail: osmohad30@yahoo.com

  3. Aquaculture Consultants Office, 9 Road 256, 11435 New Maadi, Cairo, Egypt. E-mail: aco_egypt@yahoo.com

Abstract

Desert fish farming is now taking place in aquaculture production system in Egypt. The economical and efficiently utilization of water source is a must. Also integration between fish production and plant crops is considered as one of the targets in the reclaimed areas, where the water source would be utilized first in intensive aquaculture ponds to maximize the productivity of the water unite, then use the effluent water which enriched by organic fertilizer (fish wastes) in irrigation, that means producing two crops with the same amount of water. This way of production has been first established in Egypt in the reclaimed area of Wadi Alnatroon, Bohera Governorate.

This study has been carried out in private intensive fish farm in Wadi Alnatroon, Bohera Governorate to investigate the effect of water exchange rate and the aeration system on growth performance, feed utilization and productivity of ponds (kg/ ponds and kg/m3 of water). Twelve concrete circulated ponds (250 m3 each) divided into 4 groups were assigned for applying the present study (Table 1). Each pond was stocked by 8500 fish with initial body weight of 50 g/ fish. The experiment lasted 180 days. Underground water was used to exchange water in ponds at a rate of 5, 5, 10 and 20%/ day for groups one, two, three and four, respectively. All experimental ponds were provided by paddlewheel (2 HP), where an air injector (2 HP) was associated in group 2 with also a paddlewheel. The study included the feed cost to produce one kg of fish. The results of the present study are shown in Table 2, where the highest fish productivity (4250 kg fish/ pond) was obtained by the highest water exchange rate (20% /day) this achieved 17 kg fish/ m3 , followed by group 2 and 3, which produced 3415 and 3249 kg fish/ pond, respectively. The lowest production value per pond was obtained by group No. 1 (3700 kg fish/ pond). Figure 1 shows that the highest final individual fish weight (510 g/ fish) was obtained by the highest water exchange rate (20% daily) followed by group 3, which were similar to group2 (410 and 390 g/ fish, respectively). The lowest individual final fish weigh (285 g/ fish) was observed by the lowest water exchange rate (5% daily). Feed conversion ratio improved by increasing the water exchange rate (Fig. 2) where 1.3 kg extruded feed was needed in group 4 to produce 1 kg fish, followed by group 3 and 2 (1.6 and 1.7, respectively), the 1st group showed the worst value (1.9 kg extruded feed/ kg gain). These results has been reflected on the cost to produce 1 kg fish as follow 4, 5, 5.1 and 5.9 LE (in 2007 the exchange rate of 1 $US was 5.5 LE) for groups 4, 3, 2 and 1, respectively.

Table 1. Effect of water exchange rate on the productivity of fish ponds






Group1

(5% water exchange rate/ day)



Group 2

(5% water exchange rate/ day)



Group 3

(10% water exchange rate/ day)



Group 4

(20% water exchange rate/ day)



Pond water volume(m3)

250

250

250

250

Stoking rate (fish/pond)

8500

8500

8500

8500

Survival rate (%)

98

98

98

98

Initial weight(gm/ fish)

50

50

50

50

Period of rearing (days)

180

180

180

180

Water exchange rate per day (%)

5

5

10

20

Aeration system

P.W*

P.W+ A.I**

P.W

P.W

* P.W = Paddlewheel (2 HP) injecting 4.39 kg O2/ hr

** AI = Air injector (2 HP) injecting 2.95 kg O2/ hr.
Table 2. Growth, total biomass, feed utilization efficiency and feed cost/ kg fish in the
present study.




Group1

(5% exchange rate/ day)



Group 2

(5% exchange rate/ day)



Group 3

(10% exchange rate/ day)



Group 4

(20% exchange rate/ day)



Final yield (Kg/ pond)

2374

3249

3415

4250

Net yield (kg/ pond)

1957

2832

2998

3831

Final individual weight (g/ fish)

285

390

410

510

Net weight gain (g/ fish)

235

340

360

460

Biomass (kg/ m3)

9

13

14

17

Total feed fed (kg/ pond)

3700

4700

4830

4980

Feed conversion ratio

1.9

1.7

1.6

1.3

Feed cost/ kg fish (L.E)

5.9

5.1

5.0

4.0






Water quality in terms of ammonia concentration (Fig 3) was affected by water exchange rate. The highest values were observed by group 1 (with the lowest water exchange rate), whereas slight increase in ammonia concentration was detected throughout the study period in the other experimental treatments.



The results of the present field study concluded that; higher water exchange rate in intensive fish farms has improved the productivity of the concrete circulated fish ponds, whereas with limiting water resources (5% exchange rate/day), adding two aeration systems (2 HP paddlewheel injecting 4.39 kgO2/ hr associated with 2 HP air injector injecting 2.95 kg O2/hr) in ponds has improved its productivity to reach the production of ponds with a limited 10% water exchange rate, due to the rare water resources in the Egyptian desert and which is already integrated in the plant and animal productions.




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