The present study was carried out to screen the predominant mycotic infections among freshwater fishes (Oreochromis niloticus and Clarias gariepinus) in Kafrelsheikh fish farms; with special focus on the seasonal incidence; as well as, the histopathological changes induced by the detected fungi. 500 specimens of freshwater fishes (400 O. niloticus and 100 C. gariepinus) were investigated for seasonal incidence of mycotic diseases. Mycological examination revealed the isolation of 2148 fungal isolates from 375 diseased and 125 apparently healthy fish samples (1828 mould and 320 yeast isolates), of which 1258 were isolated from O. niloticus and 890 isolates from C. gariepinus. Saprolegnia was the predominant among diseased fishes with highest prevalence in late autumn (10.68%, 6.96%) and winter (6.81%, 7.87%) in O. niloticus and C. gariepinus, respectively. However, Pencillium sp. and Aspergillus sp. were the most predominant fungi isolated from apparently healthy fishes. The highest prevalence of Pencillium sp. were recorded in winter, whileas Aspergillus showed variations between species; Aspergillus flavus, Aspergillus niger were more prevalent in summer (25.44%, 23.22%) and (26.9%, 37.44%) and Aspergillus terrus, Aspergillus fumigatus were more prevalent in autumn (5.98%, 5.67%) and (7.69%, 8.23%) in O. niloticus and C. gariepinus, respectively. Moreover, the highest prevalence of Fusarium species was recorded in spring (11.8%, 5.91%) from O. niloticus, C. gariepinus, respectively. Mucor recorded the highest prevalence in autumn (20.09%) in O. niloticus and winter (29.21%) in C. gariepinus; whileas Rhizopus was highest in summer (7.89%, 5.21%) in O. niloticus and C. gariepinus, respectively. Four genera from yeast were isolated; Candida sp. (28.44%, 36.27%), Rhodotorula sp. (36.24%, 24.51%), Cryptococcus sp. (16.97%, 20.59%) and Trichosporon Sp. (18.35%, 18.63%) in O. niloticus and C. gariepinus, respectively. The histopathological findings revealed severe degenerative changes in skin and gills with presence of fungal hyphae and spores.

The current study was established to test the possibility of using exogenous digestive enzymes (EDE) in rabbitfish (Siganus rivulatus) diets. Five experimental diets containing 34% soybean meal were prepared and supplemented with EDE at 0, 1, 2, 3, and 4 g kg -1 diet. Fish with average initial weight (± 1.1 g) were fed the test diets for 74 days. Rabbitfish offered the diets with EDE supplements exhibited significantly (P<0.05) higher growth performance, feed intake, protein efficiency ratio, protein gain, and protein retention over the basal diet. But, no significant (P>0.05) differences were observed in carcass composition and somatic parameters index with EDE supplementation. The physiological condition of fish fed diets with EDE showed that the hematocrit (%), total plasma protein and total plasma globulin were significantly (P<0.05) higher in fish fed EDE than the control group. It can be concluded that the addition of EDE in rabbitfish diets improved the growth performance, feed efficiency and health condition.

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.

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The current experiment was randomly designed as a 3×2 factorial design to investigate the effects of two fixed factor (stocking density & dietary protein level) on growth performance, feed utilization, survival rate and physiological response of African catfish (Clarias gariepinus). Fishes were allotted in 18 concrete (8×3×0.5 m 3 ; L×W×H) tanks at three different stocking density 30, 20 and 10 catfish fingerlings / m3 and fed on two different protein diets (25 and 30%). Each treatment was applied in three replicates. Fishes were fed 2.5% of biomass body weight twice/day. Results showed that growth performance, feed utilization, survival rate and hematological parameters were significantly improved with increased dietary protein level with low stocking density. The sixth treatment (high protein level 30% and lowest stocking density; 10 fish/m 3 ) exhibited the highest growth performance with no mortalities. Based on the results of the current study, it could be recommended to use protein level diet of 30% or more and stocking density of 10 catfish fingerlings/ m 3 to obtain high productivity in a short time with consequent decreased cost.

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