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.

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.

Various studies have shown the importance of using different types of Zooplankton biomasses as an additional substance in the diet of fish. In addition, the drainage water of the fish cultures could be used in plant irrigation. In this study, biomasses of water flea Daphnia magna and Gammarus pulex collected and tested, for the first time, their effect against pathogenic microorganisms and on plant germination. The results showed significant antibacterial activity of D. magna and G. pulex against Staphylococcus aureus and Pseudomonas aeruginosa bacteria, as well as antifungal activity against Alternaria solani and Penicillium expansum, which gives the possibility to be used as biocontrol against these bacteria and plant pathogenic fungi. Furthermore, both animals showed positive activity in the germination rate of Vicia faba seed, reaching 83.0 ± 3.5 and 86.0 ± 3.8%, respectively. In conclusion, the biomasses of D. magna and G. pulex are promising and effective agents for their use in the medical field against some pathogenic microbes and as stimulators of plant growth.

In recent years, global aquaculture has increased significantly, and therefore the demand for animal protein used to feed farmed fish has increased, this has led to the search for other sources of animal protein instead of fish meal. Amphipods as Gammarus are among those possible alternatives due to its abundant productivity and appropriate nutritional content, as the current study showed that its protein content was 40%, carbohydrates 27.4%, fat 5.5%, and it also contained antioxidants such as tannic acid (223.146 mg/100g) and β-carotene (21602.964 IU/100g) in addition to many essential vitamins in considerable values such as Vitamin B2 338.3842 mg/100g, Vitamin B6 (635.616 mg/100g), Vitamin B12 (419.5017 mg/100g), Vitamin A (19623.98 IU/100g), Vitamin E (177.958 mg/100g), Vitamin D (59.672 mg/100g), and Folic Acid (521.185 µg/100g). Gammarus pulex has been isolated from the natural resource (Lake Mariout), and after 90 days of rearing in tanks (initial stock: 30 individuals/liter) supplied with four different types of nests: pored wood pieces, balls of palm fibers, balls of palm leaves, and balls of nylon net "Haba net", one type for each tank. The obtained data revealed that balls of palm leaves are the best nest for rearing as it gave the highest yields (127 individuals/liter), the average obtained numbers of the different rearing tanks was 108 individuals/liter with average wet weight 2.16g/l, which means 1m3 water can produce approximately 2160g of Gammarus. A new nutritional formula was used in the current study to feed the cultivated Gammarus in its various stages, which gave good results that were reflected in its productivity and the analysis of its chemical components.

Fishmeal is the most expensive feedstuff in the aquafeed and one of the most environmentally limiting factor of aquaculture development. Therefore, the search for alternative protein sources is a continuous process. The present feeding trial was conducted to evaluate the effects of replacing fishmeal with zooplankton biomass meal (ZBM) on the growth performance, nutrient utilization, intestine, and liver histological changes of grey mullet, Mugil cephalus (initial weight of 0.10 ± 0.01 g). Five isoproteic (35% crude protein) and isolipidic (8% crude lipid) diets were formulated as the control diet (Z₀) and the other four diets (Z₂₅, Z₅₀, Z₇₅, and Z₁₀₀), where 25%, 50%, 75%, and 100% of fishmeal was replaced by ZBM, respectively. After 60 days of feeding, the final weight, weight gain, and daily growth index of the grey mullet fed the Z₁₀₀ diet were higher than those fed the control diet (p < 0.05). In addition, the better values of feed conversion ratio, protein efficiency ratio and lipid efficiency ratio were recorded in the fish fed with the Z₁₀₀ diet. Additionally, the intestinal villus length, crypts depth, and muscle thickness were significantly improved with ZBM inclusion (p < 0.05). Meanwhile, there were no histopathological changes observed on the liver when compared with the control group. From the economic point of view, dietary substitution of fishmeal by ZBM (Z₁₀₀) reduced the cost of diet formulation by 18% and the price per kg weight gain by about 40%. Overall, according to the findings of this study, substituting fishmeal with ZBM up to 100% could improve growth performance, feed utilization, gut health status, and profit ability of rearing M. cephalus juveniles.

Zooplankton is the source of life for most of aquatic organisms especially in their larval stages. Its importance come from that most fishes depend on it as a source of life after absorbance of the yolk sac. Moreover, the greatest aquatic creatures like many species of whales are filter feeders where the planktonic organisms form the main bulk of their food. The importance of zooplankton as a main source of nutrition of marine fish larvae has been long professed. Many scientists attributed the ability of a fish population to outdistance through the larval period without vast mortality as one of the primary factors determining the size of the resulting year class and hypothesized that competition for food during the larval time might be a major factor affecting survival and subsequent year class strength.