Evaluation of the three different sources of dietary starch in an extruded feed for juvenile olive flounder, Paralichthys olivaceus

Abstract

The overall performance and well-being of juvenile olive flounder were evaluated in response to three isonitrogenous and isolipidic extruded feed pellets containing either wheat flour (WF), potato (PS) or corn starch (CS), as a dietary carbohydrate source. Following the 2-week acclimation period, triplicate groups of fish (16.6 ± 0.01 g) were assigned to each experimental diet and fed to apparent satiation for 8 weeks. The results of the extruded feed pellet's physical quality tests revealed that dietary inclusion of PS could significantly enhance the water stability of the extruded feed pellets. In addition, PS and CS diets had significantly higher bulk density than WF diet. Feeding juvenile flounders with these experimental diets, however, did not induce any significant changes in their overall performance. Significantly higher serum lysozyme activity was recorded in fish fed the PS and CS diets than those fed the WF diet. Fish fed the WF and CS diets had significantly higher superoxide dismutase activity than PS group. Expression of the immune-related genes, including SOD2, EPX-L, TNF-L, IL-6, and TIPRL, was notably up-regulated in liver of fish fed the PS and CS diets compared to those fed the WF diet. Interestingly, however, an inverse expression pattern was found for the same genes in the spleen where lower expression levels were detected in the PS and CS groups than the WF group. Overall, our findings revealed that while dietary utilization of PS produced an extruded feed pellet with markedly higher physical quality than either WF or CS, neither of these starch sources were able to significantly impact the flounder's performance. Further studies are needed to elucidate the potential long-term consequences of the invoked immune response in the PS and CS groups.