Geosmin depuration from European eel (Anguilla anguilla ) is not affected by the water renewal rate of depuration tanks

Abstract

This study established that geosmin depuration from European eel is not affected by the water renewal rate of depuration tanks. A general fish bioaccumulation model extended with terms that account for effects of tank water renewal rate and system losses of chemicals, predicted strong effects of the water renewal rate of depuration tanks on geosmin depuration from European eel. Model predictions were validated in a depuration experiment with geosmin-loaded European eel (n = 95) with a mean (SD) individual weight of 134.4 (5.0) g and a mean (SD) lipid content of 33.7 (2.8) % (w/w). Fish were depurated for 24, 48 or 72 h at three different tank water renewal rates (0.3, 3.3 and 33 day À1 ). Treatments were installed by three different mean (SD) water flow rates (13.8 (1.3), 143.5 (9.2) and 1511 (80) L kg fish À1 day À1 ) over 30-L tanks. Eels eliminated geosmin from their bodies, but unlike the model predicted, this was independent of the water renewal rate of the depuration tanks. Although being eliminated from the fish, geosmin hardly appeared and certainly did not accumulate in the water of the depuration tanks as the model predicted. This observation may be explained by geosmin being eliminated from eel as metabolite rather than the parent compound. Geosmin elimination from eel seems not to occur according to the generally accepted passive diffusion mechanism for excretion of lipophilic chemicals, and geosmin biotransformation by the eel seems indicated. Clearly geosmin depuration from European eel cannot be enhanced by increasing water renewal rates of depuration tanks.

Controlling of geosmin and 2‐methylisoborneol induced off‐flavours in recirculating aquaculture system farmed fish—A review

“…In closed systems, the water renewal rate is the limiting factor for GSM depuration. However, Schram et al () reported that they did not detect any effect of tank water renewal of an eel ( Anguilla anguilla ) RAS farm on the concentration of GSM in the depuration tank.…”

“…In the case of GSM and MIB (K ow 3.57 and 3.31), the main uptake route is via the gills (From & Hørlyck, ), the gastrointestinal tract being a less important route (Howgate, ; Streit, ). Geosmin and MIB are accumulated rapidly (Johnsen & Lloyd, ; Johnsen, Lloyd, Vinyard, & Dionigi, ) in the body lipids of fish, which, it is assumed, proceeds passively, is reversible and concentration‐driven (Schram et al, ). The chemicals can diffuse freely in and out of fish via the gills, depending on the fugacity gradient between water and fish until equilibrium is reached (Howgate, ).…”

“…During depuration, concentrations of GSM and MIB in fish decrease exponentially in clean water, while GSM and MIB do not seem to accumulate in water (Schram et al, ). Typically, the volume of water is much larger compared to the amount of fish (fish density about 31 kg/m, Lindholm‐Lehto, Vielma, Pakkanen, & Alén, under review ) and it is unlikely that the excretion of chemicals affects the concentration in water.…”

“…Schram et al () suggested that metabolites of GSM and MIB might be excreted instead of only the parent compounds, explaining the reason that GSM is not detected in closed circulation systems after the depuration step. So far, there are no studies available examining GSM biotransformation in different fish species (Howgate, ).…”

“…Measures that aim to optimise the off‐flavour depuration process by increasing the rate of removal of excreted chemicals from the depuration tank will be largely ineffective if GSM and MIB are excreted as metabolites rather than the parent compounds. Instead, improved biotransformation would appear to be more successful in enhancing off‐flavour depuration (Schram et al, ). However, further research is still required to study if the rate of GSM elimination is generic across fish species.…”