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.

The future of aquaculture development is directed toward high intensification to overcome the decline in natural fishing and to provide enough protein for the increasing world population. The spread of aquaculture production and intensification requires the search for high-quality, new efficient feed ingredients with low cost and sustainable importance. Therefore, the current study aimed to detect the effects of partial or total replacement of fishmeal with amphipod meal, Gammarus pulex, on growth performance, survival percent, feed utilization, histological alteration of intestine and liver, and economic yield of grey mullet, Mugil cephalus, fry. Five diets were formulated to contain 100% fishmeal (FM), or FM replaced with 25%, 50%, 75%, or 100% amphipod meal (APM) (D₀, D₂₅, D₅₀, D₇₅, and D₁₀₀, respectively). A total of 300 grey mullet fry (0.097 ± 0.001 g), were divided into five groups (three replicates each) at an initial stocking density of 20 fry per aquaria (100 L). The aquarium’s water is renewed at a rate of 30% daily. During a 60-day experimental period, the feeding rate was 20% of body weight, which was introduced as five meals per day. Fish fed D₅₀ achieved the highest significant values of final weight (1.80 g), weight gain (1.70 g), survival (86.67%), final length (4.47 cm), and length gain (2.06 cm). In addition, the feed utilization of diets containing increasing substitution levels of FM showed that the highest protein intake (0.82 g ish⁻¹), protein efficiency ratio (0.83), protein productive value (30.65%), and the lowest significant feed conversion ratio (1.21) were recorded with D₅₀. The dose-response study revealed that the best substitution levels could range between 50% and 75%. Histological observations confirmed that the highest number of goblet cells and intestinal villi were recorded in the group fed D₅₀. No pathological effect was observed in the liver at all substitution levels. In terms of economic efficiency, the best economic conversion ratio was recorded in the group fed D₅₀. This study confirmed that 50% partial substitution of FM with APM is the ideal replacement level for grey mullet fry. In addition, the use of a new renewable alternative, such as APM to substitute FM, could relieve the pressure on the capture of wild fish and reduce the environmental impact of inland aquaculture.

Water quality describes the condition of the water, including chemical, physical, and biological characteristics, usually with regarding to its suitability for a particular purpose. The present study describes the environmental conditions of Mahmoudia canal which are the main water source for Alexandria and Behiera governorates. Water samples were collected from ten sites along the Mahmoudia canal in the year 2018 for study the seasonal variations of the water quality parameters (physicoche-mical and biological parameters). The measured physicochemical parameters include; (Turbidity, Temperature, pH, Electrical Conductivity, Total Dissolved Solids, Total Suspended Solids, Total alkalinity, Total Hardness, Nitrate, Nitrite, Ammonia, Sulfate, Phosphate, Dissolved Oxygen, Biological Oxygen Demand, Chemical Oxygen Demand, Chlorinated pesticides and some heavy metals). Phytoplankton and Zooplankton were examined as biological parameters. The values of average water quality index (WQI) of Mahmoudia canal ranged from 75.01 (poor water quality) to 132.57 (very poor water quality). According to the results of Cluster analysis, six statistically significant clusters were formed. Three groups of phytoplankton were recorded which, the annual maximum density of phytoplankton recorded in Town of Abou Hommos, while the lowest recorded in site Zawyet Ghazal Village. The highest density registered in winter (34602 U/ml), while the lowest density recorded in summer (8316 U/ml). In addition to six zooplankton groups were quantified in the analysis of the samples from ten sites, the highest density listed in summer (60000 ind./m3) ,although the lowest listed in winter (32000 ind./m3).