Fig. 1.

Experimental plan for the HC stimulus (history) and the dietary carbohydrate challenge test. Nile tilapia fry were fed either a high-protein/low-carbohydrate (HP/LC) or a low-protein/high-carbohydrate (LP/HC) diet at the first-feeding stage for 4 weeks. At week 1, fry was sampled to examine the expression of genes involved in carbohydrate and its related metabolism. See Table 1 for the list of genes and their respective primers. At the end of stimulus (4 weeks), fry were sampled to determine the glycogen and triacylglycerol contents and the expression of genes that are involved in carbohydrate and its related metabolism. Subsequently, the fish were cultured for a growth trial during weeks 5–36 after stimulus. During the growth trial, commercial diets (weeks 5–8, 40 % CP + 8 % CF; weeks 9–20, 32 % CP + 4 % CF; weeks 21–36, 30 % CP + 4 % CF) were used for feeding. Before a challenge test (week 36), the fish were sampled to examine the effects of stimulus history. During weeks 37–41, the fish were subjected to a challenge test with different dietary carbohydrate levels (37 % carbohydrates, CHO-M; 67 % carbohydrates, CHO-H). Fish sampling was performed before (week 36) and after (week 41) the challenge to determine blood metabolites, muscle and hepatic chemical composition, and expression of metabolic genes.