Is Biofloc fish a safe alternative to conventionally cultivated fish regarding metal bioaccumulation in Bangladesh?

In this study, two types of biofloc cultivated fishes (n=10) namely Anabas testudineus and Oreochromis niloticus, used water (n=6), and commercial fish feeds (n=5) from Dhaka, Bangladesh were collected and analyzed for 11 metals.The contamination level and bioaccumulation of metals to different organs of fishes were also determined. Inductively Coupled Plasma-Mass Spectrometer (ICP-MS) was used to quantify the concentration of metals in different samples. The concentration (ppb FW) range of metals in the fish samples are as follows, As (0.47-1.14), Cd (0.09-0.59), Co (0.03-0.33), Cr (0.82-4.60), Cu (0.001-7.01), Hg (0.96-3.37), Ni (1.01-10.8), Pb (2.10-4.40), Zn (0.12-73.1), Mn (1.64-18.0), Fe (23.1-261.5); and in the feed samples (ppb), As (1.56-1.91), Cd (0.09-0.39), Co (0.25-1.17), Cr (0.001-1.93), Cu (4.96-11.7), Hg (0.90-2.06), Ni (2.19-3.38), Pb (2.93-5.38), Zn (0.002-105.8), Mn (0.01-0.03), Fe (132.3-603.4). This study found fish feed as a source of metals in the Biofloc system as the metal pollution index value followed the order of fish feed>fish tank water>fish. However, the metal concentrations in the fish species and feeds were within the safe limits recommended by different international and national institutions. The highest bioaccumulation of metals in the fish species is found for Mn and lowest for Co. Fish tank water was found as hyperaccumulator for As, Cd, Ni, Zn, and Fe. On the other hand, fish-feed acts as an excluder considering the metal bioaccumulation from feed to fish except for Cr, Hg, and Mn. According to the findings, all fish organs have a considerable tendency to accumulate metals from their diet and tank water. However, human health risk assessment revealed no non-carcinogenic health hazard (THQ<1) and target cancer risk due to the consumption of these farmed fish. Thus, the consumption of the studied Biofloc fish is quite safe regarding metal contamination.