Embora a ciência da nutrição de peixes esteja longe de estabelecer um padrão geral de exigências nutricionais, a necessidade de desenvolvimento de alimentos de baixo impacto poluente há muito faz parte da agenda das comunidades científica e empresarial internacional da aqüicultura. Não só é absolutamente possível formular alimentos ambientalmente corretos, como é necessário modelar a formulação destes alimentos. Porém, é necessária absoluta acurácia para atender formulações espécie-específicas, considerando-se as interações da biologia e fisiologia nutricional das espécies com os alimentos e com as variações abióticas do meio. O conhecimento disponível sobre as mais de 200 espécies de peixe produzidas comercialmente no mundo é ainda incipiente e os sistemas de produção de peixe, nos diferentes regimes de exploração, estão implantados em todas as condições ecológicas possíveis. Neste cenário, produzir rações ambientalmente corretas é, senão impossível, pelo menos muito difícil e depende da ação coordenada e positiva de produtores, indústria da alimentação, agências regulatórias, e instituições de ensino e pesquisa para definir os parâmetros necessários à consecução deste objetivo.Although fish nutrition science is far from establishing general standards of nutritional requirements, the need for developing low impact feeds has long been included in the agenda of aquaculture's international scientific and business communities of. Not only is absolutely possible to formulate environmental friendly feeds, as it is necessary modeling the formulation of these feeds. However, it is necessary higher accuracy to develop species-specific formulations, considering interactions of the biology and nutritional physiology of the species with the feedstuffs and variations of abiotic environment. The knowledge on more than 200 species of commercially farmed fish is still incipient and fish production systems, in their most varied farming conditions, are set up in every possible ecological conditions. In this scenario, producing environmental friendly feeds is if not impossible, at least very, very difficult, depending on coordinated and positive action of producers, industry, regulatory agencies, and institutions of higher education and research to define the parameters needed to achieve this goal

Improper dietary protein and energy levels and their ratio will lead to increased fish production cost. This work evaluated effects of dietary protein : energy ratio on growth and body composition of pacu, Piaractus mesopotamicus. Fingerling pacu (15.5 ± 0.4 g) were fed twice a day for 10 weeks until apparent satiation with diets containing 220, 260, 300, 340 or 380 g kg⁻¹ crude protein (CP) and 10.9, 11.7, 12.6, 13.4 or 14.2 MJ kg⁻¹ digestible energy (DE) in a totally randomized experimental design, 5 × 5 factorial scheme (n = 3). Weight gain, specific growth rate increased and feed conversion ratio (FCR) decreased significantly (P < 0.05) when CP increased from 220 to 271, 268 and 281 g kg⁻¹ respectively. Pacu was able to adjust feed consumption in a wide range of dietary DE concentration. Fish fed 260 CP diets showed best (P < 0.05) protein efficiency ratio and FCR with 11.7–12.6 MJ kg⁻¹; but for the 380 CP‐diets group, significant differences were observed only at 14.2 MJ kg⁻¹ dietary energy level, suggesting that pacu favours protein as energy source. DE was the chief influence on whole body chemical composition. Minimum dietary protein requirement of pacu is 270 g kg⁻¹, with an optimum CP : DE of 22.2 g MJ⁻¹.

Organic acids have recently been identified as promising replacements for antibiotics in aquafeeds that promote fish growth and feed efficiency. This study evaluated the inclusion of fumaric acid (FA; 0, 5, 10, 15, 20, and 30 g/kg) in diets (350 g/kg CP; 3.4 kcal digestible energy/g) of Nile tilapia juveniles. Fish (average weight 1.7 ± 0.1 g) were distributed in three 40 L aquaria per treatment (13 fish/aquaria) in a completely randomized design. Over 35 days, the fish received the experimental diets three times daily to apparent satiety. The maximum weight gain, feed efficiency ratio, and protein efficiency ratio were recorded in fish supplemented with 14–15 g/kg FA. After 28 days, Enterobacteriaceae was registered only in the gut of tilapia without FA augmentation. Gram-negative bacteria in the fish gut decreased (p < 0.05) in fish receiving 17 g/kg of dietary FA, increased after this level. The intestinal villi height and width were affected (p < 0.05) by FA levels and feeding time. Thus, inclusion of 15 g/kg of FA was effective in promoting growth, improving intestinal morphometry, and decreasing negative gut bacteria of Nile tilapia juveniles after 35 days.