Ammonia is toxic to fish if allowed to accumulate and not-properly managed in fish production systems. Six treatments were studied to evaluate the effectiveness of applying three commercial Ammonia Removal Products (Activated Carbon, Natural Zeolite and Effective Microorganisms (EM ®)). These treatments are: (1) C, Control, (2) AC5, activated carbon at 5ppt, (3) AC10, activated carbon at 10 ppt, (4) Z5, Zeolite at 5 ppt, (5) Z10, zeolite at 10 ppt, and (6) EM400, EM at 400 ppm. European Seabass fry (240.74 mg/fish IW) were stocked into glass aquaria (50 litres each) at density of 20 fry/aquarium. Water exchange rate was 20% daily and the experiment continued for 35 days. Fish were fed on experimental diet contained 51.37% crude protein, three meals daily, and six days weekly. Data of water quality, survival and growth performance were recorded weekly. The results revealed that, ammonia removal efficiency of the tested products was significantly (P ≤ 0.05) better than control, with no significant differences (P>0.05) between the evaluated products. The best ammonia removal rate (76.60%) was obtained at Z10 treatment. Fish survival (%) ranged between 37.78% to 90% with highly significant (P ≤ 0.05) differences between treatments. The best survival (%) was obtained at EM400 (90%), while the lowest (37.78%) was obtained at AC5 and AC10 treatments. Growth performance was significantly (P ≤ 0.05) higher at (EM400, Z10, and Z5), compared with treatments (AC10, AC5, and C). It could be clearly concluded that, using Probiotics (EM ®) and Zeolite for ammonia removal might be a good potential alternative choice, while activated carbon cannot be recommended for marine fish rearing tanks in terms of low survival and growth performance and also the higher expected production cost.

Four light colors (red, white, green and blue) were tested to evaluate their effects on both body color enhancement and growth performance of Florida red tilapia (Oreochromis mosambicus × O. hornorum). Fish were stocked in 12 fiberglass tanks, (each of 2 m3 water volume), at a stocking rate of 100 fish per tank with average initial weight of 2.66 g/fish, three replicates for each treatment. Fish were fed on a commercial diet containing 25% protein, two meals per day with a daily feeding rate of 7% in the first two weeks, then reduced to 5% until the end of the experimental period (6 weeks). The results of this study reveals that there are no significant differences (p>0.05) in growth performance indexes between treatments. However, fish exposed to red color showed highest growth values. With the same trend, results of survival percent and condition factor showed no significant differences between treatments. Significant differences (p≤0.05) are observed in the whole body chemical composition between treatments. Fingerlings that are exposed to blue color has the highest value of dry matter content, while, the lowest value is observed in fingerlings exposed to red color. Feed utilization (FI, FCR and PER) do not significantly affect the lighting color, while protein and energy utilization (PPV and EU) are significantly affected. Concerning the red color accumulated in the fish body, the fingerlings which are exposed to the blue color achieved the best β-carotene value (211.25 IU/100 g fish) with highly significant differences compared with other treatments. The content of β-carotene in blue color treatment is 8, 9, and 16 folds comparing with green, white, and red colors, respectively. Also, Red tilapia fish with black spots in the blue treatment were 12%, compared with 29% in green, 56% in white and 52% in red colors.It could be concluded that cultivating Red tilapia in a full saline well water using the artificial blue color will significantly improve not only the pigmentation of Red tilapia, the quality of fish in terms of the content of dry matter, but also the protein and the energy utilization of the consumed feed.

A study was conducted to investigate the effects of natural zeolites as a water clarifier on the heavy metal removal efficiency from the underground saltwater used for rearing Dicentrarchus labrax fry. Five concentrations of zeolites were tested: 0 (Z0), 2.5‰ (Z2.5), 5‰ (Z5), 7.5‰ (Z7.5) and 10‰ (Z10). Fry with an initial body weight of 1.53±0.018 g/fish were stocked in 15 aquaria at a density of 10 fry/aquarium. The fish were fed a commercial diet (42% protein and 12.34% lipid) twice daily (09:30 and 14:00) at 5% of their body weight per day for 42 days. Growth, feed utilization, survival and heavy metal removal efficiency were evaluated. The growth performance and feed utilization indices gradually improved with increasing zeolite concentration, with the most significant (P≤0.05) values detected at Z10. The survival rate decreased significantly at Z10 compared with the control (Z0). Increasing the zeolite concentration significantly (P≤0.05) improved the removal efficiency of heavy metals in the rearing water with adsorption selectivity of Pb˃Cd˃Fe˃Cu˃Zn. Furthermore, an increase in the detoxification rate of heavy metals in fish flesh with increasing zeolite level was detected with the removal selectivity of Fe˃Cu˃Zn˃Pb˃Cd. In conclusion, it can be stated that natural zeolites can be used effectively to reduce heavy metals in polluted waters and subsequently in fish flesh in addition to improving fish performance.

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A study was performed to examine the effects of salinity on water quality, fish performance, carcass composition and haemato‐biochemical parameters in juvenile meagre, Argyrosomus regius. Fish (5.0 g) were stocked in fibreglass tanks at four salinity levels: 8‰, 16‰, 24‰ and 32‰, and fed a pelleted diet (47/17 protein/lipid) for 56 days. Results indicated that the growth, feed utilization, carcass composition and haemato‐biochemical parameters of meagre gradually improved with the increase in salinity up to 24‰ and then significantly (p ≤ .05) decreased at 32‰. The survival per cent showed a significant decrease when A. regius exposed to 8‰ salinity. An improvement with 32%, 47% and 34.1% of FCR, protein productive value and energy utilization was detected at 24‰ compared with 8‰ salinity respectively. The highest content of protein and the lowest of lipids were recorded in fish carcass at 24‰ compared with the opposite trend at 8‰ salinity. The 24‰ salinity treatment exhibited the highest value of haemoglobin (4.9 g/dl) and the lowest ratio (0.73) of albumin/globulin. The serum total protein, albumin and globulin were significantly higher at 24‰ and 32‰ salinity than those at 8‰ and 16‰ salinity groups. These findings indicate that 24‰ salinity level might be the best for meagre.

Water exchange rates were manipulated to reduce the negative effect of high stocking density adversely affects the rearing condition such as water exchange rates has to be manipulated to elevate stress factors. European sea bass juveniles with an average body weight of 4.5 g fish/m 3 were stocked at three densities (50, 100 and 150 fish/m 3 ) in 12 concrete ponds. Two water exchange rates (20% and 30% of total water volume) were applied for 18 weeks to investigate their influence on reducing the negative effect of stocking density and enhancing the water quality. The results indicated that the 30% water exchange rate was better for achieving high growth performance and feed utilization, regardless of stocking density. Water quality (total ammonia nitrogen, un-ionized ammonia, nitrite and nitrate) was enhanced, dissolved oxygen increased and all harmful nitrogen derivatives decreased when the 30% water exchange rate was applied. Additionally, the 30% water exchange rate significantly increased the water temperature (16.33°C) compared to the 20% exchange rate (14.33°C), and the final body weight, weight gain and specific growth rate were significantly increased (P<0.05) with the 30% water exchange rate. The survival rate was 97%, which was significantly the highest at the density of 50 fingerlings/m 3 at a water exchange rate of 30%. Although the feed conversion ratio, protein efficiency ratio, and protein productive value significantly improved with the 30% water exchange rate at all densities, the 100 fish/m 3 stocking density achieved the best feed conversion ratio. However, the haematological parameters showed a significant increase (P<0.05) in haemoglobin, haematocrit, white blood cells, lymphocytes, monocytes and neutrophils with a low stocking density and a 30% water exchange rate 454 Ghada A. Sallam et al. ___________________________________________________________________________________ One of the most commonly used tools to improve the yield of certain aquaculture areas and reduce the unit cost is increasing the stocking density (SD). Wide ranges of densities are regularly used for cultured sea bass, e.g., from less than 10 to more than 100 kg/m 3 , based on the rearing conditions and growth phase (Ellis et al., 2002; Conte, 2004). However, water quality is highly influenced by fish density in the culture system (especially in well-water conditions); for example, high densities can cause water quality deterioration and physical and biological stress in fish, especially when they are chronically exposed to high SDs (Björnsson and Ólafsdóttir, 2006; de Oliveira et al., 2012). The SD and water exchange rate (W ex ) have a close link with physiological responses in fish (Montero et al., 1999). Thus, a higher W ex can reduce the harmful effects of high stocking densities by enhancing physicochemical parameters such as water temperature and ammonia content (