Possibility for decreasing of mercury content in bluefin tuna Thunnus orientalis by fish culture

Abstract

The bluefin tuna tested were reared for 22 months from eggs before the beginning of the experiment, and sampling was performed every 3 months over the following year. The experimental results showed that the mercury concentration in the muscle ranged from 0.32 to 0.85 mg/g, which is lower than that found in wild bluefin tuna of a similar size. Increase in the mercury concentration corresponding to the increase in body weight was not shown, and it was quite different with wild bluefin tuna. Furthermore, no significant relationship was found between the lipid concentration and the mercury concentration in muscle. Among the internal organs of cultured bluefin tuna, the heart (0.32-0.66 mg/g), liver (0.43-0.99 mg/g) and spleen (0.59-1.0 mg/g) contained higher concentrations of mercury. It was estimated that the full-cycle cultured bluefin tuna had been fed small fish containing lower concentrations of mercury, and that the mercury concentration of tuna would be almost equal throughout the year because the effect of mercury accumulation would be weakened by body growth. Therefore, it was concluded that selecting diet fish species might decrease mercury contents in cultured bluefin tuna.

Quantifying mercury isotope dynamics in captive Pacific bluefin tuna (Thunnus orientalis)

“…The average muscle tissue THg at the longest time periods (after equilibration) is ∼12 times higher than the THg of the dietary mixture, which illustrates the bioaccumulation factor (THg concentration of PBFT white muscle tissue divided by the weight mean THg concentration of the dietary mixture). The small decreasing trend in THg concentration with time in captivity is consistent with previous studies, which reported THg concentrations in captive and farmed PBFT (Nakao et al, 2007;Lares et al, 2012;Coleman et al, 2015). These studies attributed the reduction in THg concentration to internal biodilution due to growth.…”

Mercury levels of small fishes: influence of size and catch area

“…This explains the higher mercury level found in the Pacific Ocean. As fish living in environments with high mercury levels have been shown to accumulate more mercury in their tissues than fish exposed to lower levels of mercury [10,17], bioaccumulation of mercury in marine organisms is expected to be higher in the Pacific Ocean. Consequently, the higher mercury levels in the Pacific Ocean, which may be caused by volcanic activity, could be the reason why fish caught in the Pacific Ocean had higher mercury levels than those caught in the Sea of Japan in this study.…”

“…Nakao et al [10] suggested that most mercury is included in the protein fraction, making muscle an important tissue to check, rather than internal organs, whose weight is small. For this reason, muscle was sampled for analysis in the abdominal area above the vent of the fish, because mercury is uniformly distributed in fish edible muscle [15].…”

“…For this reason, muscle was sampled for analysis in the abdominal area above the vent of the fish, because mercury is uniformly distributed in fish edible muscle [15]. Total mercury levels in fish muscle were measured using a reduction vaporizing atomic absorption method [10].…”

“…wild and cultured bluefin tuna revealed that mercury levels in cultured fish do not correspond to body weight (B0.6 lg/g) while the mercury level in wild fish arise depending on diet consumed [10,11]. However, combined with its relatively large size, the relatively high trophic level occupied by bluefin tuna means that this species still has potential to accumulate high levels of mercury [12,13].…”