Food odors alter behavioral responses and olfactory receptors expression in grass carp(Ctenopharyngodon idellus)

Olfaction,the sense of smell,is crucial for animal survival,especially in localizing prey or food.However,little is known about the fish behavioral responses to specific food odors and which olfactory receptor might be activated by the food odors.Here,we examined the evolutionary relationships and classified the subfamilies of olfactory receptors(ORs),and conducted behavioral and gene expression analysis in grass carp(Ctenopharyngodon idellus).We identified 196 intact ORs in the grass carp genome and classified them into 8 subfamilies:β,δ,ε,η,γ,κ,θ,andζ.12 representative ORs(4β,4δ,and 4ε)were highly expressed in the olfactory epithelium(OE)of 24-month-old grass carp.Behavioral exploration found that grass carp showed different behaviors to different food odors at a series of concentrations.Specifically,0.01μmol/L amino acid mixtures and 0.005×Hydrilla verticillata extracts strongly changed the preference index and swimming trajectories in 6-month-old grass carp.In addition,the two food odors stimulation differentially induced ORs expression in three tissues,especially strong in the olfactory bulb and brain.Altogether,our results suggest that olfaction plays an important role in the regulation of fish feeding behavior and provide a basis for further studies on the function and specific recognition of olfactory receptors in fish.

Characterization of odorous charge and photochemical reactivity of VOC emissions from a full-scale food waste treatment plant in China

Food waste treatment plants （FWTPs） are usually associated with odorous nuisance and health risks, which are partially caused by volatile organic compound （VOC） emissions. This study investigated the VOC emissions from a selected full-scale FWTP in China. The feedstock used in this plant was mainly collected from local restaurants. For a year, the FWTP was closely monitored on specific days in each season. Four major indoor treatment units of the plant, including the storage room, sorting/crushing room, hydrothermal hydrolysis unit, and aerobic fermentation unit, were chosen as the monitoring locations. The highest mean concentration of total VOC emissions was observed in the aerobic fermentation unit at 21,748.2-31,283.3 μg/m^3, followed by the hydrothermal hydrolysis unit at 10,798.1-23,144.4 μg/m^3. The detected VOC families included biogenic compounds （oxygenated compounds, hydrocarbons, terpenes, and organosulfur compounds） and abiogenic compounds （aromatic hydrocarbons and halocarbons）. Oxygenated compounds, particularly alcohols, were the most abundant compounds in all samples. With the use of odor index analysis and principal components analysis, the hydrothermal hydrolysis and aerobic fermentation units were clearly distinguished from the pre-treatment units, as characterized by their higher contributions to odorous nuisance. Methanthiol was the dominant odorant in the hydrothermal hydrolysis unit, whereas aldehyde was the dominant odorant in the aerobic fermentation unit. Terpenes, specifically limonene, had the highest level of propylene equivalent concentration during the monitoring periods. This concentration can contribute to the increase in the atmospheric reactivity and ozone formation potential in the surrounding air.