Growth, survival and the histology of the digestive tract of juvenile Osteoglossum bicirrhosum (Cuvier, 1829) fed three diets containing different protein and lipid levels

<p>The influence of three commercial diets with different protein and lipid contents (40&nbsp;:&nbsp;14, 45&nbsp;:&nbsp;8, 48&nbsp;:&nbsp;8 protein&nbsp;:&nbsp;lipid – P&nbsp;:&nbsp;L, in % dry weight of diet) on growth performance, survival and the histology of the liver and intestine was analysed in early juveniles of silver arowana, Osteoglossum&nbsp;bicirrhosum, reared in captivity. Individuals (initial wet&nbsp;weight–Wi&nbsp;=&nbsp;1.07&nbsp;±&nbsp;0.04&nbsp;g; total length–TL&nbsp;= 6.0&nbsp;± 0.17&nbsp;cm) were raised in triplicate (n&nbsp;=&nbsp;12 fish per tank) at 26.2&nbsp;±&nbsp;0.1°C and fed one of three commercial diets over 60&nbsp;days. At the end of the trial, survival (90.5&nbsp;±&nbsp;3.3%) and condition factor (0.5&nbsp;±&nbsp;0.02) were not affected by dietary treatments, whereas specific growth rate, TL and W gain were lower in animals fed the 40P&nbsp;:&nbsp;14L diet. Histological analysis revealed a larger accumulation of lipid droplets in the intestines of the group supplied with the 40P&nbsp;:&nbsp;14L diet, as well as a larger surface of hepatic lipid vacuoles compared to the other treatments, although no signs of steatosis were observed. Juveniles fed the 48P&nbsp;:&nbsp;8L diet displayed the lowest liver lipid accumulation; however, a protein content higher than 45% did not improve growth performance. The intestine and liver lipid accumulation of individuals fed the 45P&nbsp;:&nbsp;8L diet might indicate a more balanced lipidic metabolism. Intestine and liver histologies proved to be useful markers to identify the nutritional condition in juveniles of O.&nbsp;bicirrhosum, even when differences in nutritional composition were subtle (i.e. protein variation of 3%).</p>