Dietary uptake of geosmin in Rainbow Trout (Oncorhynchus mykiss)

Authors: DUPRE, REBECCA - Oak Ridge Institute For Science And Education (ORISE); Ardoin, Ryan; TRUSHENSKI, JESSE - Riverence Holdings Llc; JACKSON, CHRIS - Riverence Holdings Llc; Grimm, Casey; Smith, Brennan

Submitted to: Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/8/2023
Publication Date: 3/17/2023
Citation: Dupre, R. A., Ardoin, R., Trushenski, J., Jackson, C., Grimm, C., Smith, B. 2023. Dietary uptake of geosmin in Rainbow Trout (Oncorhynchus mykiss). Aquaculture. 571, 739458. https://doi.org/10.1016/j.aquaculture.2023.739458
DOI: https://doi.org/10.1016/j.aquaculture.2023.739458

Interpretive Summary: Regardless of species, ”muddy" or "earthy" flavors in fish products for human consumptions are considered signs of poor quality by consumers. For producers, these off-flavors are treated as defects which should be minimized or removed. One source of off-flavors in farm-raised fish is a chemical called geosmin, which can be found in pond water. For four weeks, Rainbow Trout were fed a diet spiked with geosmin,and fish were supplied with a continuous flow of fresh water. Results showed that geosmin can be readily absorbed into Rainbow Trout fillets through the gastrointestinal system. Higher doses of geosmin in feed resulted in significantly higher concentrations of the chemical in fillets. By incorporating geosmin into fillets in a controlled manner, future research can further investigate its effect on product acceptability and explore strategies to limit this off-flavor in farm-raised fish of any species. Furthermore, the findings of this study highlight a route of geosmin exposure that is not often considered when off-flavor issues arise.

Technical Abstract: Geosmin is a primary source of muddy/earthy off-flavors in farmed fish,which may render their eating quality unacceptable to consumers. Model systems of geosmin uptake typically consider waterborne geosmin being absorbed into fish tissues during ventilation. The present research presents evidence for dietary exposure as an alternative route of geosmin uptake into Rainbow Trout (Oncorhynchus mykiss) fillets. Fingerling trout (average initial weight of 355 g) were stocked in quadruplicate four-compartment raceways supplied with first use flow-through water (4.5 complete turnovers per hour). For four weeks, trout were provided daily feed spiked with geosmin to one of four target doses: 0 (control dose), 0.005 (low dose), 0.05 (medium dose), or 0.5 (high dose) mg geosmin/kg feed. Geosmin content of 204 total fillets (12 per combination of week and dose plus 12 sampled prior to the feeding trial) was analyzed via GC-MS, as were weekly feed and water samples. Data were also collected for feeding and consumption behaviors. ANOVA with post-hoc Tukey tests and polynomial contrast, regression, and chi-squared statistical analyses were applied to data (a=0.05). Palatability of feed did not hinder uptake at higher geosmin doses, where feeding behavior was more aggressive. Geosmin was effectively imparted into fillets after one week, and no significant temporal effect was found after four weeks. Mean geosmin concentrations significantly increased in fillets from low (mean of 26 ppt fillet-geosmin) to medium (202 ppt) to high (441 ppt) dose feed groups during the trial. Polynomial contrasts and regression modeling validated this significant positive effect of dose on geosmin uptake, with an estimated 166 ppt rise in fillet-geosmin for every log10 dose increase. As waterborne geosmin levels immediately post-feeding were conditionally independent of concentrations in feed and fillets, the hypothesis of dietary uptake as the predominant mechanism of absorption in the present experimental system was supported. Based on these findings, geosmin-spiked feeds may be used to induce repeatable levels of this off-flavor compound in fillets and serve as a model system for further investigation of sensory quality and corrective strategies to improve acceptability of farm-raised fish products.