A representative sampling of tuna muscle for mercury control

Abstract

The mechanisms of mercury accumulation and distribution in fish tissues are related to its high affinity for sulfhydryl groups in proteins. There is evidence that mercury is distributed unevenly based on the different reactivity of these groups in the various muscle proteins. Tuna fish also shows numerous specialized anatomical features including the structure of the swimming muscles and some form of endothermy, which generates variations in the mercury content between dark and white muscle and between muscle tissues with different lipid content. The aim of the study is to verify, through a suitable sub lot of Thunnus thynnus caught by a static trap in south-western Sardinia, the effective uneven distribution of mercury in the various muscles and also identify the sites representative of the entire carcass. In agreement with other authors, the results show that even in the Bluefin tuna of the Mediterranean, the site “anterior extremity of upper loin (schienale in Italian)” is representative of the mercury average content of muscle tissues as a whole.

Effects of Age, Fulton’s Condition Index (K) and Muscle Fat on Total Mercury Content in Raw, Pre-Canning and Canned Samples of Atlantic Bluefin Tuna (Thunnus thynnus)

“…The present study shows that, even in the case of Atlantic bluefin tuna, the canning process promotes a statistically significant increase in the concentration of mercury from raw samples to canned samples. The re-sults of the present study showed that also in Atlantic bluefin tuna, like Southern bluefin tuna [1][2][3][4][6][7][8][9]13,[15][16][17][18][19][20][21][22][23][24][25]29,31] and Pacific bluefin tuna [23], the weight of fish represents the best known, but not the only, variable associated with the dynamics of mercury accumulation in the muscles. In fact, at least two other components must be considered: K and the percentage of fat in the muscle.…”

“…In order to comply with the official methods of sampling and analysis for the control of the levels of contaminants in foodstuffs [18], a division in homogeneous sub-lots in relation to size and age of the specimens was carried out. The correlation between size and age of tuna was evaluated according to previous studies [8,9,[21][22][23][24][25]29,31,32]. It was found that 78.6% of the batch (n. 213 specimens) consisted of "very young" tuna, estimated to be up to 5 years old (weight range: 20.2-55.4 kg, mean ± standard deviation (s.d.…”

“…according to previous studies [19]. Through the relation between the whole weight (Ww) in kg and the straight fork length (SFL) in cm, the Fulton's condition index (K) was calculated according to previous studies [21,22]: Muscle samples of about 1 kg per specimen were taken with a transversal cut from the anterior extremity of the upper loin, as previously described [24]. All the samples were immediately frozen in a blast chiller at −50 • C and then stored at −25 • C. A total of 30 sub-samples of raw muscle of about 500 g each were analysed in August 2020, while the remaining 30 sub-samples of about 500 g each intended for canning were stored at −20 • C.…”

“…However, bluefin tunas (Thunnus spp.) are well recognized as having distinct groups of tissues [1][2][3][4][6][7][8]13,[15][16][17][18][19][20][21][22][23][24], easily identifiable based on lipid content, colour, location, and muscle structure [25]. Monitoring of mercury concentration in caught and farmed bluefin tunas shows a reduction in mercury concentration in farmed fishes.…”

Analysis of the results of research into the mercury content in fish and seafood during import-export operations in Ukraine for 2019–2021

“…Тому ВООЗ рекомендує проводити відповідні дослідження та вживати усіх можливих заходів для зниження рівнів метилртуті в продуктах харчування, особливо у рибі. Це дозволять споживачам приймати рішення щодо видів та кількості морепродуктів, які є безпеч-ними для вживання та корисними з точки зору харчування (Balshaw et al, 2007;Bosch et al, 2016;Zupo et al, 2019;Annibaldi et al, 2019;Piras et al, 2020).…”