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In the last years, there were some bacterial outbreaks occurred during the summer season of farm-raised Oreochromis niloticus at Kafr El-Sheikh and Dakahlia Governorates resulting in high fish mortalities and severe economic losses in these farms. So, this study aimed to detect the causes of the summer fish mortalities in these governorates to facilitate the diagnosis methods of study pathogens. Thirty fish farms were surveyed (20 in Kafr El-Sheikh and 10 in Dakahlia). 150 examined diseased fish (five from each farm) were succumbed for bacteriological isolation and biochemical and molecular identification. LD 50 experiments were done to detect the infectivity and pathogenicity of some strains of bacterial isolates. The obtained results cleared that O. niloticus summer mortalities were caused by mixed infections with different bacterial species. The isolated bacterial species were 9 types of bacteria; 7 gram negative bacteria; 78 (30.5%) Aeromonas hydrophila, 52 (20.3%) Pseudomonas aeruginosa, 40 (15.6%) Vibrio anguillarum, 20 (7.8%) Edwardsiella tarda, 12 (4.7%) Edwardsiella ictulari, 10 (3.9%) Pseudomonas fluorescens, 7 (2.7%) Flavobacterium columnare and 2 gram positive bacteria; 30 (11.7%) Streptococcus agalactia and 7 (2.8) Enterococcus feacalis which were the most prevalent bacteria affecting fish farms and implicated in the O. niloticus seasonal summer mortalities and LD 50 experiments confirmed the pathogenicity of some isolated bacteria. From the obtained results, it could be concluded that, the main cause of summer fish mortalities in studied farms was 81.82% gram negative bacteria and 18.18% was gram positive bacteria.

Key words:Aeromonas hydrophila, Fingerlings, Oreochromis niloticus, Refeeding, Starvation Knowledge of how fish respond to starvation periods could provide a basis for improved nutrition, rearing, disease control and thereby help to optimize Oreochromis niloticus culture. In the current study, the effect of alternative starvation-refeeding regime was monitored on some growth, hematological and serum biochemical parameters in Nile tilapia fingerlings; followed by checking the role of these feeding schedules in combating the disease challenge. The study was performed in glass aquariums at the aquaculture research unit, Sakha, Kafr El-Sheikh governorate, Egypt using 375 Oreochromis niloticus fingerlings weighing 29±0.5 gram. Fingerlings were subjected to different starvation periods (7, 10, 14, 21 days), followed by 30 days of refeeding on a commercial fish ration (25% protein). Fish growth parameters, hematological and serum biochemical parameters were recorded before starvation, before refeeding and after 30 days of refeeding. The experimental challenge was carried out to determine the effect of different starvation intervals followed by refeeding regimes on the immunity of O. niloticus fingerlings; against bacterial infection with Aeromonas hydrophila through recording mortality rates and the histopathological finding.The collected results revealed that fingerlings can recover all the hematological and serum biochemical parameter values of all food deprived groups close to the normal level of full-fed control fish; concluding that O. niloticus can easily be cultured on suitable economic short-time feeding regime with subsequent refeeding in alternate days without any significant differences in fish size and final production (reducing the food amount and cost required for production cycle). Besides, short-term starvation prior to a bacterial infection followed by subsequent refeeding could promote the defense mechanism of the fish to fight against Aeromonas hydrophila.

Poultry producers accustomed to use light colours in broiler production as atrial to increase their productivity, especially in the developing countries to cover the animal protein gap. This experiment was planned to study the effect of different blue light colour intensities (high, medium and dim) on a recently imported Indian River (IR) broilers to Egypt. In this study, 270 one-day old Indian River broiler chicks were used. The birds were exposed to high blue light intensity (HBLI), medium blue light intensity (MBLI) and dim blue light intensity (DBLI), through a monochromatic lighting system that was installed in different rooms for 24 hours daily. The birds were randomly divided and housed into three well controlled pens of 5.46 m2 with three replicates of 30 each using a density of 17 birds/m2 in the room. The results showed that the broilers reared under DBLI had a significantly (p< 0.05) higher body weight, body weight gain, Newcastle disease virus antibody titer and foot pad dermatitis with obviously, economic Feed conversion ratio (FCR) and low activities and heterophyil/lymphocyte ratio in comparing with (MBLI) and (HBLI). In conclusion, poultry producer can use dim blue light in their farms to reduce the activities and increase the productivity of the birds.