الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
A group of Nile tilapia O. niloticus with an average initial body weigh of (7 – 8 g) were obtained from the stock of earthen ponds (from a farm at Kafr El-Sheikh Governorate) and transported to the aquaria located in the fish laboratory of Kafr El-Sheikh governorate. Fish were maintained in these aquaria for 2 weeks before the beginning of the experiment for acclimatization purpose. The fish were fed during the acclimatization period on the basal diet (25% crude protein) at a rate of 3% of the body weight daily, at 2 times daily. The experimental treatments were tested at two aquaria (replicates) for each. Fish will be stoked at a density of 7 fish / aquarium. Partial or complete replacement of fishmeal (0, 25, 50, 75, and 100%) by whole crayfish meal and / or duck weeds meal in Nile tilapia fish diets was carried out to investigate its effect on water quality parameters, growth performance, feed and nutrients utilization, blood picture, body and muscles composition, silica and some heavy metals. from the foregoing results, it would be clear that the 6th diet (25% freshwater crayfish meal as partial replacer of dietary fish meal) was significantly the best concerning fish bodyweight gain, relative growth rate, feed and protein intakes; as well as blood hemoglobin, hemotocrit, total protein, and globulin besides highest protein and lowest fat in whole fish and fish muscles. This was followed by the 11th diet (50% substitution with mixture (1/1) of duckweed meal and freshwater crayfish meal), which was responsible for highest final body weight, bodyweight gain, daily body weight gain, and feed conversion, which may be reflected the economical diet by decreasing feed costs to produce one Kg fish bodyweight gain. This leads to recommend the partial replacement of fish meal in Nile tilapia diets with 25% crayfish meal or 50% mixture of crayfish meal plus duckweed meal (1/1). These diets were responsible for better results than control and it is to expect that they will reduce the costs of fish feeding and production for the lower prices of either duckweed meal or freshwater crayfish meal comparing with the very expensive price of fish meal.