Comparative transcriptome analysis of olfactory epithelium in large yellow croaker: Evidence for olfactory adaptation to feed phagostimulant in fish

Abstract To investigate the olfactory adaptation to feed phagostimulant in fish, we utilized three types of phagostimulants. Dimethyl-beta-propiothetin hydrochloride (Dmpt), taurine (Tau) and l -tryptophan (Trp) mixed with feed for the diets of large yellow croaker (Larimichthy crocea) for 7 days. The fish displayed a significant behavioral preference for 0.50% Dmpt, so we mixed feed with 0.50% Dmpt, 3.50% Tau and 1.63% Trp, and the fish showed a downtrend of mean percentage of ingested feed (MPIF) in Dmpt and Trp group of 7 days, but showed an up- and a downtrend of MPIF in Tau group of 7 days. Then, we sequenced olfactory epithelium tissues of Day 7 to detected the differentially expressed genes (DEGs), and found 37 (6 up- and 31 down-regulated) olfactory receptor related DEGs in Dmpt group, 22 (18 up- and 4 down-regulated) in Tau group and 16 (15 up- and 1 down-regulated) olfactory receptor related DEGs in Trp group; we analyzed the expression level of significantly changing genes of these DEGs in 7 days by RT-qPCR, and we found that the expression of genes showed a downtrend in 7 days of Dmpt and Trp group but an up- and a downtrend in 7 days of Tau group. According to the behavioral adaptation process and adaptive expression trend of olfactory related receptor DEGs, we sequenced the transcriptome of olfactory epithelium in Tau group of Day 1 and Day 5, and analyzed the olfactory transduction pathway. Based on the expression level of DEGs, especially OR, ACIII, CAMKII, CNG and CNGA3 in this pathway, we speculated the positive olfactory effect of Tau and the higher concentration of Ca2+ entering into olfactory sensory cell in Day 5, which suggested that the fish had been medium adaptation stage in Day 5 and later adaptation stage in Day 7. Using this data, we initially prove the olfactory adaptation to feed phagostimulant (phased and discontinuous types of olfactory stimulants) in fish, and provide new insights into utilization of phagostimulant in aquaculture.