الفهرس 
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Abstract
This study was carried out in the Alexandria University. Three experiments were conducted to study the effect of feeding rates, dietary protein and energy levels and amino acid supplementation rate on growth performance, feed utilization and body composition of sea bass (Decentrarshus laborax The first experiment:<The aim of this experiment was held to study the effect of feeding rates on growth performance and feed utilization for sea bass (Decentrarshus laborax). Also, their protein and energy requirements were determined. Each treatment was replicated in three aquaria and using pelleted diets. Sea bass had initial weight of 0.08 g. This experiment was lasted for seven weeks. Fish were given feed three times daily at a feeding rate of (5, 10, 15, 20, 25, 30%) of fish biomass. Fish were hand fed six days / week.
The results showed that:
1. Weight gain and final body weight (FBW) of sea bass increased significantly with increasing dietary feeding rate up to 20% with no differences between 20, 25% and 30%.
2. The lower body weight was found at 5% feeding rate with the higher mortality rate.
3.
The lipid content of sea bass increased significantly with increasing feeding rates from 5% to 20% with no differences between 20%, 25% and 30%.
4.
The best growth rate and specific growth rate were observed with 20% feeding rate and no significant deferences were found between 20, 25 and 30% feeding rate.
5.
6. The moisture content of sea bass body reduced significantly, but the protein body content of sea bass increased significantly with increasing feeding rates up to 20% and decreased with increasing feeding rates from 25 and 30%, but no significant differences were found between 25 and 30%.
The body weight of sea bass increased by increasing protein and energy intake in the diet from 22 – 90 mg protein / 1g BW daily and from 150 – 600 cal grosses energy / 1g BW daily. The increase in body protein and energy with the increase in protein and energy intake could be expressed by the equation: Y = 6.21x – 22.8 and Y = 0.93x – 22.8 for protein and energy, respectively.
7.
from the regression analysis, maintenance requirements could be calculated at (Y= zero). It could be calculated in the range of 3.67–3.83 mg protein/ and 24.49–31.79 cal gross energy /1g of the fish BW daily were the maintenance requirements of sea bass (0.08g IBW).
The conclusion of this result indicates that the best feeding rate was found at 20% BW for sea bass 0.08g IBW. Thus, 90mg protein and 600cal gross energy / g BW daily could be recommended as the maximum growth requirements for sea bass larvae. Also, from the same data, it could be recommended that sea bass larvae (0.08g initial BW) require 3.75mg protein / g BW and 28.14 cal gross energy /g BW daily as maintenance requirements.
The second experiment:
This experiment was held to study the effect of three dietary protein levels (25, 35 and 45%) combined with three energy levels (250 and 300 kcal/100g diet) at a 3×2 factorial experiment, on growth performance and feed utilization of sea bass (Decentrarshus laborax). Each treatment was replicated in three aquaria using pelleted diets. Sea bass had initial weight of 0.8 g. This experiment was lasted for five weeks. Fish were fed 3 times daily to satiation 7 days per week. Fish were weighed every two weeks.
The results showed that:
1.
2.
Weight gain of sea bass increased significantly with increasing dietary crude protein levels up to 45% and decreased significant with increasing energy levels from 250 and 300 kcal/100 g diets.
Feed conversion ratio (FCR) improved with increasing dietary crude protein level up to 45% and no differences between 250 and 300 kcal/100g diets were found.
3. The protein and lipid content of sea bass increased significantly with increasing dietary crude protein level from 25% to 45% and energy level from 250 to 300 kcal/100g diet . But, protein content of sea bass was decreased with increasing energy level.
4. The best SGR was observed with 45% dietary crude protein with 250 kcal/100g diet.
5. The moisture content of sea bass was significantly lower at 250 kcal energy level and 45% protein level.
6. Final body weight (FBW) of sea bass increased significantly (P<0.05) with increasing dietary crude protein levels up to 45% with 250 kcal/100 g diets.
7. ER% increased significantly (P<0.05) with increasing dietary crude protein levels, but it decreased with increasing energy levels.
The conclusion of this result indicates that the best protein level and energy level for sea bass (0.8 g BW) is 45% and 250 kcal, respectively in terms of total weight gain. Lower protein level has given better protein utilization and a protein sparing effect but tended to result in reduced weight gain and feed intake, when compared with diet containing higher protein levels at 45%.
The third experiment:
In this experiment, the crude protein level of 35% and energy level of 300 kcal obtained from the second experiment had been used to prepare the five diets. This experiment was held to study the effect of amino acids supplementation rate on growth