European perch (Perca fluviatilis) fed dietary insect meal (Tenebrio molitor): From a stable isotope perspective

Stable isotope analysis was conducted to investigate stable isotope ratios of carbon (delta C-13) and nitrogen (delta N-15), diet-tissue discrimination factors of carbon (Delta C-13) and nitrogen (Delta N-15). Bayesian mixing models were performed to assess relative contribution of insect meal and other ingredients to the development of tissues of European perch (Perca fluviatilis). Accordingly, four experimental formulations, characterized by the increasing inclusion levels of yellow mealworm (Tenebrio molitor) larvae meal (TM) at 0, 6.8, 13.5 and 20.3% as replacement for fishmeal at 0 (TM0), 25 (TM25), 50 (TM50) and 75% (TM75), respectively, were fed to juvenile perch (initial bodyweight, 20.81 +/- 3.36 g) in a recirculated aquaculture system for 105 days. delta C-13 and delta N-15 of TM were -16.75 and 3.53% and significantly distinguished from other terrestrial and marine feed components (P < 0.05). Inclusion of dietary TM did not affect Delta C-13 value in blood and liver (P > 0.05) but did reduce in muscle (P < 0.05), whereas Delta N-15 was significantly increased with the increasing inclusion level of TM in all tissues (P < 0.05). The growth of perch had a significant negative relationship with diet-muscle Delta N-15. The contribution of TM to muscle (7.7 +/- 3.8%) was comparable to its dietary inclusion (6.8%) in TM25 but double in the blood (13 +/- 6%). TM appeared to be an essential ingredient incorporated into liver, as its contribution was consistent or higher than dietary inclusion (TM25: 25.4 +/- 12.1 vs. 6.8%; TM50: 31.1 +/- 14.9 vs. 13.5%; and TM75: 29.4 +/- 14.4 vs. 20.3%). The higher inclusion levels of TM (more than 6.8%) did not elevate its contribution to muscle, blood, and liver (probability, P-BIC < 0.95) but significantly decreased that of fishmeal in all tissues (P-BIC > 0.95). Soy-derived ingredients, soybean meal and soy protein, were an important ingredient in the development of all tissues regardless of dietary TM. The present study provided insightful information on the role of various diet components in perch tissues, which could underlie further development of aquafeed formulations for emerging perch farming in Europe.