الفهرس 
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Abstract
Chapter I. selected managerial approaches to cope with fish stressors, a historical review
No one can deny or ignore the interactions between the environment, pathogen, and host as promotors for the health status of living individuals, including fish, when they existed in an equilibrium status. However, during stress, such equilibrium is dispersed. As a result, a cascade of physiological events of an organism’s body follows to cope with the situation and returning to homeostasis. Several stressors such as biological or chemical agents, external and/or internal stimuli, and polluted environmental conditions could elicit the physiological stress responses. The primary stress response in teleost includes rapid changes in circulating levels of catecholamines and corticosteroids accompanied with diminished immune response and increase diseases susceptibility to not only viruses, bacteria, parasites, but also fungi. In this chapter, three major variables were reviewed in the light of operational biosecurity standards with particular concern of hatcheries, storage of fish seeds, and/or intensification. The first variable was dealing with reducing the mechanical stressor exemplified in brood stocks’ handling during artificial spawning process by using different anesthetics. Different aspects concerning types of anesthetics, mode of administration and actions, advantages and disadvantages, and their toxicity were screened. Sequentially, biological stressors illustrated in water mold infections that concise the catastrophic crises of saprolegniosis in fish hatcheries, came as the second stress variable selected. In this respect, the chapter covered fish saprolegniosis from three historical perspectives: epidemiology, diagnosis, and prevention/control. from a historical and epidemiological perspective, selected molds pathogenic species including, two genera, saprolegnia and achylia were described. Additionally, the vulnerable hosts, global distribution, and mode of the disease transmission were outlined. from a broader standpoint, the most predisposing elements linked to the disease’s prevalence, pathogen(s) virulence, and the disease pattern were also covered. Consequently, various technical tools utilized for disease pattern studies, conventional and advanced molecular laboratory diagnosis, and immunological parameter modifications in a sequential manner in several decades. The chapter announced the hazardous impacts on the ecosystem developed by misusing antimycotic agents, especially from the perspective of saprolegniosis control. Therefore, it provided an overview of the application of natural antifungal substitutes. Finally, the chapter shed light on approaches for water quality enhancement as an impressive aid for minimizing environmental stress variable and magnifying the beneficial use of fish holding facilities, particularly through using magnetic treated water. To ensure a sustainable and cost-effective applicable method, history, mode of action, advantages, and risk factors of magnetic treated water were illustrated for its application.
Chapter II. Evaluation of certified selected crude herbs as anesthetics in Egyptian freshwater fish hatcheries
This chapter described field trial application experiments that were carried out in Egyptian fish hatcheries to introduce clove (Syzygium aromaticum) and thyme (Thymus vulgaris) as fish anesthetics. Such research work was conducted at Abo-Saleh fish hatchery, Beni-Suef Governorate, Egypt during the period from April to May after approval of Competent authorities of Lakes and Fish Resources Protection and Development Agency, Ministry of Agriculture (http: //www. gafrd.org). The anesthetic effect trials were carried out during the artificial propagation of C. idella, Ctenopharyngodon idella, and broodstocks. To determine the proper anesthetic dosages of both selected herbs, in vivo toxicity tolerance tests were conducted using C. idella fingerlings prior to field trial applications. Crude clove and thyme were studied at dosages of 0.5, 1, 2, and 2, 4, 8 g/L, respectively, for field application trials. For each concentration, three replicates were built up along with their control values. In pilot study, the obtained results showed toxic levels of clove at dosages of 1 and 0.5 g/L after exposure time of 24- and 48-hours prolonged bath, respectively. The picture patterns did not look different with thyme at dosages of 2 and 1 g/L after elapsing the same time of exposure. For both crude clove and thyme, the estimated 96-LC50 was approximately 15 and 12 hours, respectively when fingerlings exposed to 1 and 2 g/L, respectively. Based on the toxic tolerance assay, all dosages of the two chosen herbs were able to successfully induce various stages of unconsciousness and achieve deep anesthesia with varying exposure and recovery times at all field trials. Instantly, anesthetic baths containing 2 and 8 g/L crude clove and thyme, respectively, successfully induced deep anesthesia and safe full recovery within considerable short period, 10 and 12 minutes, respectively. Prolonged lower dosages baths of 0.5, 1 and 2, 4 g/L crude clove and thyme, respectively, required long exposure times (20-28 minutes) since recovery times were minimized (15-20 minutes). The chapter exhibited the unique methodologies used in the represented study that provide credibility and confidence when introducing crude clove and/or thyme as anesthetics in Egyptian fish hatcheries.
Chapter III. Antifungal potential of some natural herbs
Saprolegniosis has a substantial concern in freshwater aquaculture, particularly hatcheries as it is responsible for severe mortality and economic losses. Various chemical compounds are used to deal with the disease; however, they are not preferred for their hazardous impacts on fish, humans, and ecosystems as well. Recently, a drastic loss in their egg hatchability percentages with mortality pattern in produced fry characteristic to saprolegniosis were noticed. The current study estimated in vitro and in vivo, the potential antimycotic activities of crude and aqueous extracts of clove (Syzygium aromaticum) and thyme (Thymus vulgaris) against Saprolegnia australis and Achylia bisexualis. Both herbs aqueous stock solutions were eventually performed by decoction method. The minimal inhibitory concentrations (MICs) of both herbs’ aqueous extracts were detected by agar plate diffusion method. The capability of both herbs aqueous extract to kill the selected water molds was investigated with different time points of exposure. Based on in vitro findings, two in vivo field trials were designated to evaluate the efficacies of crude clove and thyme, first, on the fecundity and hatchability of fertilized C. idella eggs. The second trial was to estimate the antifungal potential against fungal infection during artificial eggs incubation. Additionally, experimental treatment trials were conducted in parallel to estimate the anti-saprolegniosis effect of selected crude herbs in artificially infected fingerlings. Special concern was taken into consideration for the toxic concentration levels and the 96-LC50 of both herbs that elucidated from aforementioned chapter (chapter II). Generated results showed a significant inhibition of S. australis and A. bisexualis at a concentration of 10% in clove (0.8 g/100 mL) and thyme (3.2 g/100 mL) aqueous solutions. However, both herbs aqueous extracts exhibited fungicidal activities and killed both fungi at a concentration of 50% of their stock solutions (4 and 16 g/100 mL of clove and thyme, respectively). Incubated eggs exposed to concentrations of 2 and 8 g/L of clove and thyme exhibited high percentages of fecundity and hatchability of 94.33±2.33, 79.66±2.60 and 90.33±2.60, 70.66±1.76 %, respectively. In addition, clove and thyme at concentrations of 2 and 4 g/L could safely protect incubated eggs and hatched fry from being attacked by either S. australis or A. bisexualis, respectively. Despite clove and thyme at concentration ranges of 0.2 0.25 and 0.5 0.8 g/L provided a safe indefinite bath, 0.5 and 1 g/L induced anesthesia after 24 hours of exposure. Interestingly, the successful treatment of saprolegniosis experimentally infected C. idella fingerlings was achieved at doses of 0.25 0.5 g/L for clove, and 0.5 g/L for thyme with wide margin of exposure time that might reach 7 days that decreased to one day by the dose increase. At all levels, the former doses of both herbs experienced acceptable percentages (7090% for clove and 80% for thyme) of the disease cure with reasonable times of exposure. Ultimately, clove and thyme in both crude and aqueous forms could introduce safe, less costly, environmentally friendly, and easily applications into freshwater hatcheries.
Chapter IV. Potential enhancement of stocking density, water quality and growth performance of O. niloticus raised in magnetic treated water
In recent years, water scarcity is considered a worldwide challenge that hinders aquaculture industry sustainability and economic flourishing. Besides, the lack of clean water areas together with its poor-quality parameters drastically limits the global food productivity, particularly freshwater fish yield. In this respect, several advanced technologies have been emitted recently to deal with this obstacle, however, high financial support for their sustainability deprives their application on a large scale. As a result, the current chapter aimed to evaluate the probability of intensifying Nile tilapia (O. niloticus) fingerlings at different levels including storage, rear, and productive using magnetic treated water units. Such a unique value might be valuable in case of using static magnetic devices of inexpensive cost. Thus, the units in the presented study designed to permit fish sustainable storage and productivity at different intensive levels with limited water loss, especially in case of static device that needs neither energy nor filter replacement. Each established unit consisted of four compartments, three oval-shaped tanks where O. niloticus fingerlings were kept during the experimental period, and a fourth cylindrical-tank that was supplemented with biological filter and submersible water pump. The later tank acted as a collection and distribution tool for transporting magnetized water to experimental tanks and receiving the recurrent water from them. The magnetic device was oriented between both submersible pump and the experimental tanks in one directional way through well-constructed PVC pipes along with variable valve types. On the experiment operation, the three oval-shaped tanks were designated as group set A, B and C each received 50, 75, and 100 fingerlings, respectively. Similarly, the control unites represented the three tanks D, E, and F that were prepared in the same manner as their corresponding experimental ones without instillation of the magnetic device. The experimental period was twelve successive weeks; however, it was hypothetically subdivided into four, eight, and twelve weeks to simulate achieving the storage, raising, and productive potentials on various O. niloticus stocking densities, respectively. Depending on their weight change, fingerlings were fed at rate of 4% of their body weight on the starting experimental point and sequentially for nine weeks, then this rate decreased to 3% until the end of the experimental period (12th week). Growth performance parameters, including weight gain (WG), food conversion ratio (FCR), and specific growth rate (SGR) were measured every 2 weeks. The dissolved oxygen (DO) and periodical syphoning was performed weekly at two constant time points to remove waste with replacement of the same amount of water that was removed. The total ammonia nitrogen (TAN) and nitrite concentrations were measured once per week and recorded. In terms of mortality monitoring, different abnormal behaviors and cumulative mortality were recorded daily, and the percentages of survival were calculated. According to the obtained results, there were significant increase in survival rates among group set A, B, and C representing 99.331.15, 97.331.34, 92.002.00%. These findings explain the effect of stock intensifications on survival rates; however, survival rates in control groups experienced 88.002.67, 86.002.00%, 84.006.08, in group D, E, and F, respectively, reflecting the potential effect of magnetic treated water on the survival. In addition, all experimental groups were significantly higher in growth performance parameters in comparison with their corresponding controls; however, group set C showed the highest WG, SGR, and FCR representing 110.005.00 gm/fish, 111.135.55% per day, and 1.170.15, respectively. Regarding water quality parameters, there were significant differences in DO concentrations and total water replacement among the experimental groups and their controls; however, no significant difference in TAN and nitrite concentrations could be detected among them. At all tested levels, the obtained results magnified potentials of magnetic treated water on aquaculture in different aspects, particularly on stocking densities. As a result, stocking of O. niloticus fingerlings to reach the juvenile stage at a rate of 142.86 individual/m3 safely in magnetic treated water, could be employed for storage purposes for a period not less than one month. from rearing and production prospectives, the results obviously declared that O. niloticus fingerlings might be raised until reach juvenile and/or subadult individuals with acceptable and permissible limits for survival rates and water parameters, respectively. Indeed, further studies are needed to establish magnetic treated water in aquaculture of O. niloticus to achieve marketable size production level.