Developing a cost-effective diet to sustain optimal growth is considerably important in aquaculture; an increasing demand for cost-effective aqua feeds has surfaced. In an intensive culture system, over 50% of the production cost constitutes feed cost. Therefore, the importance of carbohydrate as the cheapest and most available source of energy will be highlighted. However, the consumption of high levels of dietary carbohydrate by fish may adversely affect and hamper the fish growth performance. Furthermore, excess amounts of dietary carbohydrates in the diet of some fish species lead to fat deposition via stimulation of lipogenic enzyme activities. In addition to carbohydrate level, other factors that may affect the carbohydrate utilization of fish are the molecular complexity and forms (raw or cooked) of carbohydrates. For instance, our study showed that Pangasianodon hypophthalmus fed with raw form of carbohydrate had better growth performance than fish fed with cooked form of carbohydrate. At the same time, the whole-body lipid content of the P. hypophthalmus fed with cooked carbohydrates was significantly lower than that of the fish fed with raw carbohydrates. Overall, most fish species, especially omnivorous and herbivorous fish, have utilized starch or dextrin more efficiently than glucose. Meanwhile, several studies have shown that some fish species utilize gelatinized or cooked starch better than raw starch. Nevertheless, the exact mechanism that is responsible for the differences in carbohydrate utilization remains unclear.
Researchers worldwide have been performing experiments to investigate and define the optimum carbohydrate level, source, and form (raw or cooked) of carbohydrates, specifically for each fish species. They have also been evaluating the optimum ratio of dietary carbohydrate to lipid or protein to optimize the utilization of carbohydrates in fish nutrition