An investigation into the occurrence of geosmin responsible for earthy–musty taints in UK farmed rainbow trout, Onchorhynchus mykiss

Earthy–musty taints have been reported in edible fish around the world. While this has no adverse health effects on either the consumer or the fish, it does have a profound effect on consumer acceptance and marketability. Earthy–musty taints have been reported in farmed rainbow trout in the UK but little was known about the source of the problem. In this study it was found that geosmin (GSM) was the main compound associated with the seasonal occurrence of earthy taints in UK farmed trout. GSM production occurred upstream in rivers supplying water to fish farms and was at its highest concentration (∼25 ng l−1) during the warmer summer months. Fish tainted with GSM above the sensory threshold (0.9 μg kg−1) were typically found to have between 1.0 and 3.0 μg GSM kg−1 fish, with a maximum observed level of 7.2 μg kg−1. Levels of 2-methylisoborneol were negligible in terms of its potential to cause taint. In a river-fed northern UK farm the seasonal build up of an epilithic Oscillatoria sp. was linked to tainting episodes. Rivers supplying tainted farms were classified as being eutrophic and had very low N/P ratios. Temperature and phosphates levels were positively correlated with levels of GSM in inflow waters.