Ornamental fish, Cyprinus carpio, fed with fishmeal replacement Ptecticus tenebrifer and Tenebrio molitor

The effects of Ptecticus tenebrifer and Tenebrio molitor (PTM), as alternative fishmeal, on the growth performance, haematological values, biochemical and immune response and gut microbial diversity of Cyprinus carpio L. were investigated. Two hundred and forty hatchery‐reared juvenile C. carpio were divided among four experimental diet groups, formulated with the insect replacements: Control—30% fishmeal; Treatment 1—20% fishmeal + 10% PTM; Treatment 2—10% fishmeal + 20% PTM; Treatment 3—30% PTM. C. carpio fed 30% PTM had the highest final length and the largest increase in length. The red blood cell count was the highest in 10% PTM (0.92 M/µL) and lowest in the control group (0.23 M/µL). Fusobacteria was the dominant gut bacterial phylum, followed by Bacteroidetes, Firmicutes and Proteobacteria. Cetobacterium somerae was the dominant gut bacterial species, and its relative abundance was significant in the 10% and 30% PTM treatments. The relative abundance of Bacteroides massiliensis was the highest in the control group while there was decline in the treatments with PTM. These results suggest that P. tenebrifer and T. molitor as a fishmeal replacement lower the biochemical oxygen demand and chemical oxygen demand in the culture tanks and increase the length and change the gut microbiome of C. carpio.