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The formulator of aquatic diets is part of a continuous search for alternative protein sources instead of depreciated fish meal. The utilization of zooplankton as a feed ingredient is an interesting trend due to their high-quality protein content and abundance of essential nutrients. The current study aims to investigate the effects of partial and total replacement of fish meal (FM) by Dahpnia magna meal (DMM) on growth performance, feed utilization, histological, and economic status of mullet, M. cephalus, larvae. In addition to the control diet, 100% FM, D0, four diets containing DMM at different levels were used: 25% (D25), 50% (D50), 75% (D75), and 100% (D100) replacement of fish meal. A total of 300 larvae (0.097 ± 0.001 g) were equally divided into five groups (three replicate per each group) at a density of 200 larvae m−3. The aquariums were renewed at a rate of 30% daily. During the 60-day experimental period, all larvae were fed their respective diets at a level of 20% of live body weight, five times a day (9.00 a.m., 12.00, 15.00, 18.00, and 21.00 p.m.). The results indicated that compared to D0, fish fed D75 recorded the highest significant value of growth, and feed utilization parameters, while fish fed D100 achieved the lowest feed cost and incidence cost, and the highest profit index and economic efficiency ratio. A strong correlation was reported among weight gain, feed conversion ratio and fish meal replacement with DMM; R2 = 0.94 and 0.91, respectively. The fit regression model representing mullet response to FM replacement with DMM is a poly-nominal regression model with maximum response at 75–100%. The histological investigation of the intestine revealed an improvement of histomorphometric indices and goblet cell number with increasing DMM inclusion levels. These findings confirmed that 75% to 100% partial substitution of FM with DMM is the ideal replacement for mullet, M. cephalus, larvae for improving fish growth performance and feed utilization.

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Little is known about the diversity of Calanoida, Copepoda, in different habitats of the north-western Red Sea. In this study, biodiversity of Calanoida, Copepoda, during the cold and warm seasons of 2017, were observed at 12 stations belonging to four different habitats (coral reef (CR), sheltered shallow lagoons (SSL), seagrass (SG), and open deep-water (ODW) habitats) in the Hurghada shelf, north-western Red Sea. SSL habitats were the most affected by environmental conditions, especially temperature, salinity, and depth. Some calanoid species were restricted to certain habitats, others were adapted to live in more than one habitat, while some species showed a wide distribution in all habitats. ODW habitats showed maximum diversity and density of the calanoid species. The effects of temperature and salinity were distinct in the SG and SSL. The results clearly showed that different Red Sea habitats affected the biodiversity of calanoid copepods.

Aquaculture ecosystem assessment is a major key for successful aquaculture Planning. There are many aquaculture farms constructed in Egypt, but because of the non-sufficient studies about the environmental conditions of aquaculture ecosystem assessment, many projects achieved negative results and had low economical returns. The present study was conducted to evaluate the aquaculture ecosystem assessment of irrigation water of El-Mahmoudia Canal, Alexandria, Egypt. The result indicated that temperature (24.65±0.4°C), DO (5.38±0.20mg/l), COD (14.40±4.5mg/l) and BOD (2.86±0.20 mg/l) were in the optimum range for O. niloticus. Chlorophyll a, b and carotenoids were 10.449±0.953, 4.685±0.704 and 2.374±0.054 μg/g, respectively. The biochemical composition of plankton showed that protein, lipid and carbohydrate were 37.7±3.39 %, 16.33±0.85%, and 11.23±2.63%, respectively. Moreover, SFA, MUFA and PUFA were 70.29±4.07%, 11.172±0.132 %, and 18.55±0.525 % of total fatty acids, respectively. Zooplankton community showed that rotifers and copepods configured the main bulk of zooplankton community (95.9% to the total zooplankton community). These conditions are considered the ideal recommended conditions for cultivation of Oreochromis niloticus that started with 100,000 fingerlings (distributed as 4.76 fish/m 3 of earth pond) for six months with 82% survival rate with final yield of 21.3 ton/1.6 hectare.