Effects of low fishmeal diets on growth performance, blood chemical composition, parasite resistance, and gene expression in the tiger pufferfish, Takifugu rubripes

The rising price of fishmeal and the need for sustainable use of fishery resources have encouraged efforts by the aquaculture industry to identify alternative protein sources including plants and single cell organisms. This is particularly the case for the tiger pufferfish, Takifugu rubripes, which is fed a high level of fishmeal as the protein source. In this study, we compared four possible replacement diets: in three diets, fishmeal was reduced from 77% to 47% and replaced mainly by plant (PP), bacterial (BAC), or yeast (LY)-derived ingredients; in the fourth, reduced to 20% and replaced mainly by yeast (HY). Growth performance, blood chemistry, transcriptomic responses in the liver, and resistance to the parasite Heterobothrium okamotoi were compared in 360 cultured tiger pufferfish (9.8 months old at the start of the experiment). After a 3-month feeding trial, the HY-fed fish showed increased standard lengths (p = 0.015) and body weights (p = 0.004) compared to control fish fed the standard FM (77% fishmeal) diet. At the end of the feeding trial, FM-fed fish had a mean hematocrit (Ht) of 29.3 ± 5.6%; HY-fed fish had the lowest mean Ht of 25.2 ± 5.1% (p = 0.005). Mean total cholesterol levels in BAC-, LY- and HY-fed fish were lower than in control fish (p = 0.008, 0.004, and 0.024, respectively). In contrast, no significant difference was found for triglyceride, total protein, and glucose levels among the groups. Subsequently, 150 individuals were subjected to artificial infection with H. okamotoi; no significant differences were found for mean parasite counts and Ht values between fish fed the experimental diets and the control fish. Analysis of gene expression in the liver showed that the gene hmgcra was significantly up-regulated (based on a log2 fold change threshold) in HY-fed fish compared to FM-fed fish. Overall, the analyses indicate that a low fishmeal diet in which 71% of fishmeal is replaced mainly by yeast meal (i.e., containing 40% of yeast meal in total mass) may be a suitable replacement for the commercial FM diet as it promotes growth but does not induce severe deleterious effects.