Non-specific immune parameters and physiological response of Nile tilapia fed ß-glucan and vitamin C for different periods and submitted to stress and bacterial challenge.

This study attempts to describe the effects of different administration periods of dietary ß-glucan and Vit C on the non-specific immune response, physiological parameters and disease resistance of Nile tilapia against Aeromonas hydrophila infection. Therefore, a feeding trial (288 fish) was conducted to determine the best administration period (7, 15, 30 and 45 days) for a Nile tilapia diet supplemented with 0.1% ß-glucan and 600 mg Vit C/kg diet. After the administration period, three different groups of 96 fish were exposed to one of the following three stresses: cold-induced stress, transport-induced stress, and A. hydrophila challenge. Hematological, biochemical and immunological responses were analyzed before and/or after stress. Cold-induced stress increased cortisol levels and reduced the leukocyte count in fish fed the test diet for seven days compared with the other periods. After transport-induced stress, fish fed the test diet for seven days required more hours to return to the baseline levels of cortisol and neutrophils. Moreover, independently of the administration period, fish needed 24 h for leukocyte and glucose levels to return to the initial values. The lowest survival after bacterial infection was observed in fish test diet for seven days. Based on fish hematological and biochemical responses, diet supplemented with 0.1% of ß-glucan and 600 mg of Vit C/kg fed for at least 15 days is recommended for Nile tilapia especially when fish are likely to encounter transport-induced stress, and this stress was more severe than cold-induced stress or bacterial challenge.

Exigência em fósforo disponível para alevinos de tilápia do Nilo / Dietary phosphorus requirement for fingerlings Nile Tilápia

O fósforo se destaca como um dos minerais mais importantes na nutrição animal. Apresenta-se pouco disponível em alimentos de origem vegetal por estar quimicamente ligado a outros minerais e nutrientes, em que se denomina fósforo fítico ou fitato. Desta forma, objetivou-se avaliar diferentes níveis de fósforo disponível em rações para alevinos de tilápia do Nilo (Oreochromis niloticus), por meio do ganho em peso, do consumo de ração aparente, da conversão alimentar aparente, da eficiência alimentar, da sobrevivência e da composição química da carcaça. O delineamento experimental foi inteiramente casualizado, com seis tratamentos (0; 0,25; 0,50; 0,75; 1,00 e 1,25 por cento de fósforo disponível) e cinco repetições. As rações, utilizadas para avaliar os diferentes níveis de fósforo disponível, foram formuladas exclusivamente com alimentos de origem vegetal, sendo isoprotéicas (30,0 por cento PD), isoenergéticas (3.300kcal de ED kg-1) e contendo a mesma relação cálcio:fósforo. Conclui-se que, para alevinos de tilápia do Nilo, o nível mínimo de 0,75 por cento de fósforo disponível nas rações proporciona melhor desempenho produtivo e composição química da carcaça.

Phosphorus is considered one of the most important mineral in animal nutrition. In vegetables feedstuffs this mineral can be less available because his chemistry connection with other minerals and nutrients, named the phosphorus phytic or phytate. Thus this research was aimed evaluating different levels of available phosphorus in diets for Nile tilapia (Oreochromis niloticus) fingerlings based on weight gain, feed consumption, feed conversion ratio, feed efficiency, survival and body composition. The experimental design was completely randomized with six treatment (0, 0.25, 0.50, 0.75, 1.00 e 1.25 percent of available phosphorus) and five replicates. The rations used to evaluate the different levels of available phosphorus were exclusively formulated, using vegetables feedstuffs, to contain 30.0 percent PD, 3300kcal of DE kg-1 and the same rate between calcium:phosphorus. Based on these results, 0.75 percent of available phosphorus in Nile tilapia fingerlings diets determines a better growth performance and body chemical composition.