tas1r3 is the determinant element in fish feeding preference. (A) Schematic of the sampling timeline in grass carp before and after the feeding habit transition (FHT) from carnivores of chironomid larvae to herbivores of Hydrilla verticillata. (B) Expression of tas1r3 in the intestinal (n = 6), brain (n = 4), and oropharyngeal (n = 8) tissues of grass carp before or after the FHT from carnivory to herbivory. Grass carp before and after the FHT were sampled when they reached a body length of 2.82 ± 0.18 cm and 6.21 ± 0.63 cm at 46 and 116 days post hatching, respectively. (C) Generation of two independent knockout lines of zebrafish, tas1r3-1 and tas1r3-2, contained deletions of 1 bp and 11 bp, respectively. (D) Predicted protein sequence encoded by the wild-type control or the two tas1r3 mutated zebrafish. (E) Relative expression of tas1r3 in the oropharynx, brain, and intestinal tissues of the wild-type control or tas1r3-deficient zebrafish (n = 3). (F–I) Assay of food intake in zebrafish fed duckweed. (F,H) Images of wild-type control and tas1r3-deficient zebrafish before feeding duckweed, respectively. (G,I) Images of wild-type control and tas1r3-deficient zebrafish after feeding duckweed for 12 h, respectively. (J) Amount of duckweed consumed by wild-type control or tas1r3-deficient zebrafish in 12 h (n = 10). (K) Total food intake of soybean meal diet by wild-type control or tas1r3-deficient zebrafish (n = 3). (L) Feeding rate of soybean meal diet consumed by wild-type control or tas1r3-deficient zebrafish (calculated on a body weight basis per day; n = 3). (M) Experimental equipment for analyzing the biting times of fishmeal and grassmeal blocks for zebrafish. (N) Biting times of fishmeal and grassmeal blocks in control and tas1r3-deficient zebrafish (n = 8). (*) P < 0.05, (**) P < 0.01, (***) P < 0.001, (ns) not significant.
