Effects of stocking density and water exchange rates on growth performances, production traits, feed utilization and body composition of mono-sex male Nile tilapia, Oreochromis niloticus (L.) cultured in concrete tanks  

Deyab M. S. D. El-Saidy , Ebtehal El-Sayed Hussein
Department of Poultry Production, Faculty of Agriculture, Minufiya University, Shebin El-Kom, P.O.Box 32516, Egypt
Author    Correspondence author
International Journal of Aquaculture, 2015, Vol. 5, No. 3   doi: 10.5376/ija.2015.05.0003
Received: 10 Feb., 2015    Accepted: 26 Mar., 2015    Published: 27 Apr., 2015
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El-Saidy and Hussein, 2015, Effects of stocking density and water exchange rates on growth performances, production traits, feed utilization and body composition of mono-sex male Nile tilapia, Oreochromis niloticus (L.) cultured in concrete tanks, International Journal of Aquaculture, Vol.5, No.3: 1-13 (doi: 10.5376/ija.2015.05.0003)


A 44-week randomized factorial design 2 x 3 x 2 ( two water exchange rates, three stocking density and two replicates) rearing trial was conducted in concrete tanks with average initial weight and length of 7.5 ± 1.2 g/fish and of 8.9 ± 0.5 cm/fish of mono-sex male Nile tilapia, Oreochromis niloticus , to examine the effects of two water exchange rates and three stocking density on growth performances, production traits, feed utilization and body composition. Twelve concrete tanks 4 m3 each were stocked with either 200, 300 and 400 fish for each tank to give a stocking rate of 50, 75 and 100 fish /m3, respectively and mentioned at 8L/min. or 12 L/min. water exchange rates. The results revealed that, growth performance and feed utilization parameters were significantly (P£ 0.01) the best at the lowest stocking density. No significant differences (P > 0.05) were found between water exchange rates in terms of growth performance, feed utilization and all production traits. The lowest stocking density (50fish/m3) had significantly the best feed utilization parameters. There were no significant differences between it and the stocking density of 75fish/m3. Whole fish body composition % of protein, fat and ash contents were significantly (P £ 0.05) influenced by stocking density but did not influenced by water exchange rates. From the above results it can be concluded that, stocking density of 75 fish /m3 of mono-sex male Nile tilapia reared at either 8L/min or 12L/min. water exchange rates exhibited the highest net profit and would seem to be the most desirable density under this system conditions.

Nile tilapia; Stocking density; Water exchange rates; Growth performances

Tilapias can become the worlds most important warm water cultured fishes (FAO, 1980). Among all cultured tilapia species, Nile tilapia, Oreochromis niloticus has emerged as the single most important species. The attributes, which make Nile tilapia so suitable for fish farming, are its general hardiness, ease of breeding, rapid growth rate, ability to efficiently convert organic and domestic wastes into high quality protein, and good taste. (Yi et al. 1996). For optimizing production from a system, a number of factors which are directly related to the stocking density must be considered. These factors are the physio-chemical condition of water, the production system, the types and the size of rearing tanks, the water exchange rate, the size of the fish and the quantity of the ration have been particularly emphasized (Trzebiatoowski et al. 1981).
Studies on the relation between stocking density and growth of tilapia have been numerous (Youssif (2002). The optimal stocking density of certain species for obtaining the highest possible yield depends on the amount and the quality of food available (Zonneveld and Fadholi, 1991). The increases in stocking density become possible by the introduction of oxygen depletion (El-Saidy and Gaber 2002b). High-density culture of tilapia has been successful (Youssif 2002), but comparing results is difficult because individual studies do not address the full complex of parameters. Honer et al. (1987, a & b), indicated that high density fostered faster growth but, with slightly greater variance than low-density culture in juvenile and adult tilapia. Wallace et al. (1988) found that rearing fingerling salmonids at very high densities reduced the phenotype variance while Bagley et al. (1994) observed more rapid growth, increased genetic variance and reduced environmental variance.
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 m3. 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 (4m3) to give a stocking density of 50, 75 and 100 fish/ m3 with duplicate tanks per treatment for either 8L/min. or 12 L/min. water exchange rate as follows:
Tank #
Water exchange rate
Stocking density (fish/tank 4m3)
200 (50fish/m3)
300 (75fish/m3)
400 (100fish/m3)
200 (50fish/m3)
300 (75fish/m3)
400 (100fish/m3)

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 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 pe
International Journal of Aquaculture
• Volume 5
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