A 3 × 3 factorial experiment was conducted with Mozambique tilapia. Oreochromis mossambicus (Peters), using satiate feeding with 25%, 30% or 35% dietary protein concentrations each with three energy concentrations 10.5,12.6 or 14.7 kJ per g of purified diets. Protein‐to‐energy ratios (P/DE ratio) ranged from 17 to 33.4 mg protein kJ−1 of digestible energy (DE). Diets were fed to triplicate random groups of 15 fingerlings for 62 days in glass aquaria. Improvement in both weight gain and feed conversion rate (FCR) was achieved when dietary protein increased (P < 0.05), while increasing dietary energy concentration reduced feed consumption and increased mortality (P < 0.05). Protein efficiency ratio (PER) increased as dietary protein decreased and as dietary energy increased (P < 0.05). P/DE ratio correlated positively with gain, energy retention (ER) and feed consumption (r= 0.96,0.96 and 0.73 respectively) and negatively with feed conversion rate (FCR), protein productive value (PPV), protein efficiency ratio (PER) and mortality (r= ‐0.93, ‐0.95. ‐0.91 and ‐0.84 respectively). Weight gain had a positive relation with feed consumption (r= 0.82). The optimum P/DE ratio in purified diets for Mozambique tilapia for rapid growth, efficient feed conversion and maximum retention of protein and energy appears to be approximately 23.8 mg of protein kJ−1 of DE.

Nile tilapia, Tilapia nilotica (L.), were fed eight isonitrogenous diets in two laboratory experiments at the Faculty of Agriculture (Saba Basha), Alexandria University, Alexandria, Egypt. The diets were: (A) mixture containing 28% protein from both animal protein (fish meal) and plant protein (soybean meal and cotton seed meal) as a source of protein; (B) mixture free of animal protein; (C) mixture B supplemented with essential amino acids (EAA) (methionine and lysine); (D and E) composed of diet C supplemented with 5% and 3 5% oil respectively; (F and G) composed of diet C supplemented with emulsified or saponified 3-5% oil respectively and (H) mixture composed of diet C plus non-extracted rice bran instead of wheat flour as a source of energy without adding oil.Growth performance (energy and protein retention and protein efficiency ratio) decreased with the animal protein free diet B. Supplementation of methionine and lysine to diet C improved growth performance and feed utilization as well as addition of oil and treated oil but 5% oil and 3-5% saponified oil increased mortality of the tingeriings by 46-27% and 20% respectively. Diet F gave the lowest mortality and the highest growth, energy and protein retention and protein efficiency ratio.

Two experiments were carried out to determine protein and energy requirements of striped mullet (Mugil cephalus) larvae for maintenance and maximum growth. In experiment 1 a diet containing 38% dietary crude protein and 2.45 kcal metabolizable energy / g was fed at seven incremental rates [1-13% of body weight (BW) daily] to larvae (0.195g initial BW) for 5 wk. In experiment 2, seven isocaloric diets containing (14-38% crude protein levels) were fed at satiate rate of feeding to larvae (0.2g initial BW) for 6 wk. In experiment 1, Striped mullet BW increased linearly as feeding rate increased, up to 34.61mg protein and 345.6cal gross energy / g BW daily (r 2 = 0.99), and also as dietary crude protein increased up to 26% in experiment 2 (r 2 = 0.99). The relationships between BW gain (Y) and the increase of protein and energy intake (X), could be expressed by the equations Y = -58.06 + 16.20 X for protein and Y= -57.98 +1.62 X for gross energy. Also, the increase in body protein and energy (Y) with the increase of protein and energy intake (X) could be expressed by the equations Y = -11.33 + 2.68 X; r 2 = 0.98 for protein and Y = -85.67 + 3.48 X; r 2 = 0.99 for energy. From the mathematical models, maintenance requirements of striped mullet (0.195g initial BW) could be estimated as Y= 0 to be 3.6 -4.2 mg protein /(g BW .d) and 24.6 -35.8 cal gross energy /(g BW .d). Thus the data could recommend 3.9mg protein and 30.2cal gross energy /g BW daily as maintenance requirements for striped mullet larvae of 0.195g initial BW. Also, from the same data 34.6mg protein and 345.6 cal gross energy /g BW daily could be recommended as the maximum growth requirements for the same striped mullet larvae. The data of experiment 2, indicate that 26 % dietary crude protein is the dietary crude protein needed for maximum growth and feed efficiency of 0.2g striped mullet fed at incremental dietary crude protein levels from 14-38%.

A preliminary trial and two experiments were carried out to study the effect of heat-treated feed and exogenous zymogen on the survival and growth of grey mullet, Liza ramada (Risso), larvae. The ®sh were held in glass aquaria supplied with continuous aeration and salt water, which was changed daily. Two test diets (40% crude protein) formulated from commercial ingredients were used. In the preliminary trial, diet A was either heat treated in an autoclave using a maximum pressure of 1.2 kg cm ±2 for 15 min, or supplemented with exogenous zymogen at rates of 0%, 2%, 4%, 6% or 8% of the diet. In experiments 2 and 3, four heat treatment times (0, 10, 20 or 30 min) using the previous pressure and three exogenous zymogen supplementation rates (0%, 2% or 4%) were evaluated in a 4 Q 3 factorial arrangement for effects on the survival and growth of grey mullet using diet B. Zymogen and vitamins were added to the diets after heat treatment. In addition to survival and growth, dissolved oxygen, temperature and salinity were measured periodically through the study. The grey mullet larvae were introduced to the treatments 24 h after transportation to the laboratory in experiment 2 and after 3 weeks acclimatization in experiment 3. In the preliminary trial, signi®cant differences in survival rates were observed after 7 days for larvae maintained at heat-treated diet A and diet A supplemented with 4% exogenous zymogen. In experiment 2, sig-ni®cant differences in weight gain corresponded to increasing dietary zymogen in diet B. Likewise, the percentage of survival rate increased signi®cantly starting from week 2 as zymogen increased in diet B. Heat treatments in diet B had no signi®cant effect on weight gain of grey mullet after 2 weeks. However, signi®cant differences in survival rate corresponding to heat treatments were observed for grey mullet larvae after 4 weeks in experiment 2. Diet B heat-treated for 20 min with 4% zymogen gave the best results for larval survival rate and growth. Although the larvae were acclimatized for 3 weeks to salinity using the best diet of the second experiment before starting the third experiment, the same results were observed after 3 weeks. Further experiments must be performed to con®rm the best conditions for acclimatization.

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