Age structure and growth of bluefin tuna (Thunnus thynnus, L.) in the capture-based aquaculture in the Mediterranean Sea

The principal objective of this study was to estimate the age and growth, length-weight relationships and condition factors of the Mediterranean bluefin tuna (Thunnus thynnus) in a capture-based aquaculture farm and to reveal possible differences among farmed (reared in sea cages for 18months), fattened (reared in sea cages for 6-7months) and wild specimens. Moreover, to determine the age composition of the fish destined for fattening and farming operations with the current lack of demographic information makes the bluefin tuna stock assessment extremely difficult. For this purpose, a total number of 2096 specimens (ranging from 102 to 295cm in fork length and from 33 to 540kg in round weight) were sampled, from the Greek Bluefin Tuna Farm (GR 01/2004), in the Ionian Sea (38° 26' 0.07″ N, 21° 1' 48.85″ E), during the five year period 2007-2011. In addition, length and weight literature data from wild specimens captured in the central Mediterranean Sea were analyzed. The results revealed high percentage difference in weight between wild and reared in sea cages bluefin tuna of the same fork length, which reached a maximum of 43.9% in large specimens. The condition factor of the reared in sea cages bluefin tuna ranged from 1.24 to 3.16 with a mean value of 2.04±0.19. The mean condition factor of the farmed specimens (1.92±0.17) was lower than that of the fattened specimens (2.08±0.15). This difference was consistent both in younger and older specimens in the sample. Estimated ages that were obtained using the caudal vertebrae of 619 reared in sea cages specimens ranged from 5 to 18years. It was observed that the age of fish has a significant impact on the condition factor. The comparison among the mean condition factor values of each age class revealed that older fish (10-20years old) present higher values than younger ones (5-9years old). With a view to estimating the precision of the aging method, the Average Percent Error (APE) and the Coefficient of Variation (CV) were calculated (APE=1.89% and CV=2.46%). The von Bertalanffy growth model was fitted to mean lengths at estimated ages and the growth parameters were determined (L∞=360.3cm, k=0.083yr-1, t0=-0.942yr). © 2013

Do fattening process and biological parameters affect the accumulation of metals in Atlantic bluefin tuna?

The objective of this study was to determine the current levels of heavy metals and trace elements in Atlantic bluefin tuna muscle tissues and how they are influenced by the fattening process and various life history parameters to ascertain whether the concentrations in muscle tissue exceed the maximum levels defined by the European Commission Decision and to evaluate the health risk posed by fish consumption. A total of 20 bluefin tuna reared in sea cages, ranging from 160 to 295 cm in length and from 80 to 540 kg in weight, were sampled from a bluefin tuna farm in the Ionian Sea. The condition factor K of each specimen was calculated and their age was estimated. Heavy metal and trace element (Hg, Zn, Fe and Cu) contents were determined in muscle tissue using cold vapour atomic absorption spectrometry and flame and graphite furnace atomic absorption spectrometry. The total Hg concentrations ranged from 0.28 to 1.28 mg kg–1 w/w, Zn from 5.81 to 76.37 mg kg–1 w/w, Fe from 12.14 to 39.58 mg kg–1 w/w, and Cu from 0.36 to 0.94 mg kg–1 w/w. Only 5% of the muscle samples of tuna contained Hg above the maximum level laid down by the European Commission Decision. Moreover, 15% of the muscle samples contained Zn above the maximum level, while Fe and Cu concentrations were within the acceptable tolerable guideline values. The reared bluefin tuna had lower concentrations of Hg than the wild ones from the Mediterranean Sea. Hg and Fe concentrations showed a positive relationship with size and age of bluefin tuna, whereas negative relationships were found for the concentrations of Zn and Cu. The estimated dietary intake values of the analysed metals were mostly below the derived guidelines. © 2015 Taylor & Francis

Mercury concentrations in reared Atlantic bluefin tuna and risk assessment for the consumers: To eat or not to eat?

This study determines the levels of total mercury in muscle tissue from 268 reared Atlantic bluefin tuna in the Mediterranean Sea, detects variations on mercury concentrations in relation to biological parameters and rearing period and evaluates the health risk posed by fish consumption taking into consideration the size, age and rearing period. A total of 30 pooled samples were analyzed. The total Hg concentrations ranged from 0.49 to 1.60 mg/kg w.w. and showed a significant positive relationship with the size and age. It was found that the longer the rearing period, the lower the mercury concentration. The total Hg exceeded the maximum level defined by the European Commission Decision in a proportion of 40.0%. Since the value of Target Hazard Quotient was higher than 1 in all different groups (medium, large, 6 months and 18 months reared specimens), the maximum possible safe weekly consumption (400 g) is suggested. © 2020 Elsevier Lt