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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.

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.

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