CSIR research on mercury in fish informs consumer choices

A CSIR study has found that several fish sold in South Africa’s retail stores contain mercury levels well above World Health Organization guidelines. The CSIR has produced an advisory to guide consumers on the number of meals they can safely eat for different types of fish species based on a meal size of 227 g.

The CSIR has initiated research on the concentrations of mercury in fish sold in South African retail stores. The research will provide the public with advice on how many servings of fish commonly available in retail stores they can safely consume. This will allow people to make informed decisions on the type of fish they consume.

CSIR researchers purchased fish from retail stores in Durban over a period of 11 months. They purchased whole fish to correctly identify the species, but in cases where only fish steaks were available, they took DNA samples to later verify the species. The fish were measured, weighed, dissected and subsamples were analysed for the presence of mercury.

The researchers used the test results to produce a table, which advises consumers of the number of meals they can safely eat for different types of fish species.

The results showed that swordfish had the highest mercury concentrations in their tissue. This is primarily because they are apex predators and accumulate all the mercury in the fish that they eat. CSIR researchers recommend that people eat no more than one meal of swordfish every second month and that children should avoid eating swordfish altogether.

The lowest mercury concentrations were found in yellow tail, west coast sole and canned tuna and those can be eaten 12 – 16 times per month without any risk.  Other low-risk species that people can eat 4 – 8 times per month include red roman, steenbras and hake. Kingklip, yellow fin tuna and cape salmon had relatively high concentrations of mercury and can be consumed 2 – 3 times per month.

This research is ongoing and the CSIR will be analysing more fish species and other seafood products while also looking at their omega 3 fatty-acid content.





Contact Person

Dr Brent Newman

Key Concept

Bioaccumulation refers to the accumulation of substances, such as pesticides, or other chemicals in an organism. Bioaccumulation occurs when an organism absorbs a - possibly toxic - substance at a rate faster than that at which the substance is lost by catabolism and excretion.