الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Tilapias are the second most important fish species for aquaculture after the carp around the globe. This is due to their high growth rates, having high productivity, being prolific breeders,
being easy to culture, completing their life cycle in captivity, tolerance to environmental stress and high market demand. Stocking density is one of the paramount importance factors in
aquaculture as it directly influences survival, growth performance, health status, water quality, food supply and environmental conditions and production.
In the recent years, closed aquaculture systems have acquired interest as an eco-friendly technique to produce fish .This is because these systems have very low or zero-water exchange and controlled inputs (e.g. feed) and outputs (e.g. waste), and system parameters, such as temperature, pH and dissolved oxygen levels can be managed more easily than in traditional open
ponds .
Therefore, The current study, is therefore, designed to evaluate the growth, survival and total production of fry and fingerlings and adult of the Nile tilapia reared in) haba under
different stocking densities. Also, determination the most proper stocking densities for Nile tilapia reared in closed systems biofloc tank technology (BFT) and recirculating aquaculture
systems (RAS) and the effect of biofloc technology on Nile tilapia growth under different stocking densities.
The first experiment was conducted in habas with an area of 1*3*4 m3, placed in earthen pond with an area of quarter acre. The height of water in the pond is one and quarter meter, while the height is one meter in the haba. Different growth stages of Nile tilapia (fry, juvenile and adult) were raised under two stocking densities (20 and 40 fish /m3). Fish was fed a diet
containing 30% crude protein. Data was collected to assess the impact of stocking density on survival and growth of fish in terms of body length, body weight and condition factor. The
obtained results were as follows:
1. All tested water quality parameters were suitable for reared Nile tilapia fish by two stocking densities at three different age stages.
2. At the end of the experiment, the mean final weight for Nile tilapia fish at the three different age stages (fry , fingerlings and adult) ranged between [88.94±0.26, 187.23±0.64 and 234.13±0.59 (g/fish)], respectively at the lowest stocking density(20fish/m3
) and[75.79±0.78,170.27±1.36 and 191.68 (g/fish)], respectively at highest stocking density (40 fish /m2). The mean final weight wassignificantly (P<0.05)
at low and high densities as shown in Table 4.3. The highest values of the growth performance for Nile tilapia fish were recorded at the lowest stocking density at all age stages, followed by highest stocking density at the all age stages and there were statistically significant difference between all treatments (P <0.05).
3. Means and their standard deviations of the fish length (cm) of fry, fingerlings and adult of Nile tilapia reared at two stocking densities are Similar to the results of fish weights,
means of fry, fingerlings and adult length of Nile tilapia reared at stocking density 20 fish were all longer than those reared tilapia at stocking density 40 fish/ haba and the
differences were significant, as indicated by the values of the T-tests for the three fish stages.
4. Means and their standard deviations of the condition factor (K-value) of fry, fingerlings and adult of Nile tilapia reared at the two stocking densities of 20 and 40 fish/ haba were
studied. The K values obtained were greater than one, suggesting that the fish were in 62 good condition. Surprisingly, means of K-values of fry, fingerlings and adults reared at
stocking density 40 were higher than those obtained for their counterparts reared at stocking density 20, and the differences accounting for 0.23, 0.38 and 0.72, and they were significant as indicated by the values of T-test (-3.71, -11.63 and -38.89), for the
three fish categories, respectively.
5. The highest value of condition factor was for those stage Nile tilapia fry, followed by stage Nile tilapia fingerlings followed by stage Nile tilapia adult at low and high fish density, respectively and there was statistically significant difference between all treatments (P <
0.01).
6. Means, standard deviations and T values of initial weight (IW, gm), final weight (FW, gm), total gain (TG, gm), average daily gain (ADG, gm), specific growth rate (SGR, %), feed intake (FI,%), feed conversion ratio (FCR), protein intake (PI), protein efficiency
ratio (PER), energy intake (EI), total energy gain (TEG), protein gain (PG , Number of Fish/Haba, production kg/M, production kg/ haba for fry. fingerlings and adults Nile tilapia were studied. In the case of fry, the abovementioned parameters were all larger in
fry reared at stocking density 20 than those of fry reared at stocking density 40, except PER, production kg / M and production kg/ haba, differences between both stocking densities were significant (P<0.05) as shown by the values of T-test. Parameters of adults followed the same trend with different magnitude, where those reared at stocking density
20 were larger than the corresponding values obtained for adults reared at stocking density 40, except IW, PER, production kg/M and production kg/haba, which showed slightly lower values at stocking density 20. The differences between these parameters for
adults reared at both densities were significant as indicated by the values of T test.
7. In terms of body chemical composition, there were significant differences were observed
between all treatments in dry matter, crude protein, lipid and ash content and energy content. Proximate chemical composition high values in Nile tilapia fingerlings which was rearing at low stocking density (20 fish /m3
) were larger than which was rearing at
(40 fish /m3), except the DM%, EE%, which were slightly larger in the later stocking density. Differences between both stoking densities were significant
The second experiment was carried out in 1000 L tanks for a duration of 98 days. Two fish aquaculture systems were used, namely biofloc technology (BFT) and recirculation aquaculture
system (RAS). The production of tilapia using BFT were tested for three densities: 35 (T1), 50 (T2) and 70 (T3) fingerlings/m3.