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Modelling growth as a function of feeding rate (FR) could be one of the most important tools for fish farms, because this knowledge allows growth to be maximized, or the feed conversion ratio (FCR) to be minimized, thereby improving profits. All growth models should include the three principal variables involved in growth: initial body weight, temperature and feeding rate. The thermal-unit growth coefficient (TGC) already includes water temperature variation and initial body weight. Studying variation in TGC for fish fed the same diet, but at several feeding rates provides interesting information for modelling. Six different trials were conducted where gilthead sea bream of several different initial weights (24, 38, 50, 110, 220 or 289 g) were fed increasing amounts, and growth and the conversion index response were measured. The TGC response was modelled as a function of FR, and both asymptotic and quadratic responses were examined. The asymptotic model, TGC 9 1000 = 2.037* (1Àe (À0.8*(FRÀ0.22) ), had an adjusted R 2 value of 96.18, whereas the quadratic model, TGC 9 1000 = À0.381 + 1,715 9 FRÀ0,382 9 FR 2 , had an adjusted R 2 value of 96.42. Simulations of the FCR and the economical profitability index (EPI) were conducted to provide tools for maximizing efficiency and profitability, and the results suggest that these tools will be useful for future investigations.

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Three hundred rainbow trout (242.9 ± 6.9 g) were randomly assigned to 12 fibreglass tanks (25 fish/tank). The fish were fed, for 231 days (feeding level: 0.74 % average bw), four experimental diets, containing increasing levels of coconut oil: diet A 0 %, diet B 6 %; diet C 12 % and diet D 13 %, as replacements of herring oil and cod liver oil. Weight gains of fish were > 3 g d-1 and FCR lower than 1.5, for all treatments. No significant difference was observed in the main car- cass traits and whole body composition, but whole fish energy content significantly increased in fish fed diet D (10.68 KJ g-1). Different dietary fatty acid profiles had significant effects on the rainbow trout muscle contents of C10:0, C12:0, C14:0, total n-3, and the main ratios: SFA/USFA; DHA/EPA; DHA/AA, n-3/n-6, but not on total fatty acids content of the muscle

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The effect of DPDE ratio in diets for rainbow trout, Oncorhynchus mykiss (Walbaum), was investigated. To evaluate growth and body composition, groups of trout were fed three experimental diets with a constant level of gross energy (25.4 & 0.12 MJ kg-' dry matter (DM)) and different digestible proteiddigestible energy (DPIDE) ratios (diet A, 16. 35; diet B, 17.21; diet C, 18.23 g MJ-I).Fat, protein and energy digestibility coefficients were not affected by the DPDE ratio of the diets. Growth and feed utilization improved markedly as dietary DPDE ratio increased ( P < .01). The efficiency of fat, protein and energy utilization tended to increase with increasing DPIDE ratio of the diets.Nitrogen discharge in effluent water per kg of weight gain was not affected by dietary treatments (mean values for: diet A, 29.9; diet B, 29.8; diet C, 29.1 g N kg-' weight gain) while phosphorus discharge in effluent water fell using diets with a higher DPDE ratio (mean values for: diet A, 7.3; diet B, 6.7; diet C, 5.9 g P kg-' weight gain). Effect of extrusion processing and steam pelleting diet on pellet durability, pellet water absorption and the physiological response of rainbow trout. Aquaculture, 25,[185][186][187][188][189][190][191][192][193][194]. ISMEA (1 992) Aquaculture 92 ~ Ofjicial Effect of digestible energy on nitrogen and energy balance in rainbow trout. Aquaculture, 50,89-101. Ketola, G. (1982) Effect of phosphorus in trout diet on water pollution. Sahonids, 6, 12-15. Kiaerskou, J. (1991) Production and economics of low pollution diets for the aquaculture industry.