Fish Isn't That Good For The Brain

You may have been told that fish is one of the best foods for the brain. Unfortunately, this could not be further from the truth as fish is often riddled with potent neurotoxins – regardless of where it is sourced.

Heavy Metals in Fish & Neurotoxicity

First, it should be known that the type of mercury that shows up on hair mineral analysis is methylmercury, and in my experience is directly correlated to one's fish and shellfish intake (no fish or shellfish these days are free of mercury, the only difference is some are worse than others for sure). Hair mineral analysis only shows methylmercury (aka organic mercury), and the inorganic mercury (aka “metallic mercury”) that is in amalgam/mercury fillings does NOT show up on hair mineral analysis (urine or blood must be done to show that type)

Next, it should also be known that I see hair cadmium levels move up and down in lockstep with hair mercury levels, so it is very likely that cadmium comes along with mercury in fish and shellfish.  A reduction in fish and shellfish intake generally results in a proportional decrease in hair mercury and hair cadmium levels.

There are many businesses out there that rely on the sales of fish and shellfish products, that try to say that "organic mercury"--aka methylmercury--is not toxic.  Will someone please go tell that to these birds?

Altered pairing behaviour and reproductive success in white ibises exposed to environmentally relevant concentrations of methylmercury

Methylmercury (MeHg) is the most biologically available and toxic form of mercury, and can act as a powerful teratogen, neurotoxin and endocrine disruptor in vertebrates. However, mechanisms of endocrine impairment and net effects on demography of biota are poorly understood. 

Here, we report that experimental exposure of an aquatic bird over 3 years to environmentally relevant dietary MeHg concentrations (0.05–0.3 ppm wet weight) resulted in dose-related increases in male–male pairing behaviour (to 55% of males), and decreases in egg productivity (to 30%). Dosed males showed decreased rates of key courtship behaviors, and were approached less by courting females in comparison to control males.
[...]
These results are of interest because (i) MeHg exposure is experimentally tied to demographically important reproductive deficits, (ii) these effects were found at low, chronic exposure levels commonly experienced by wildlife, and (iii) effects on reproductive behavior and sexual preference mediated by endocrine disruption represent a novel and probably under-reported mechanism by which contaminants may influence wild populations of birds.
[...]
The exposure levels we used in this study span the exposure rates reported for several avian studies, suggesting that our findings are relevant to many free-ranging bird populations [14,22,47]. MeHg exposure may therefore routinely lead to altered demographic patterns in wild bird populations. MeHg-induced reproductive deficits in birds have until now been attributed to altered parental behavior or embryonic death. Our results demonstrate that a sizeable proportion of net reproductive deficits can result from effects of MeHg exposure on sexual behavior and/or sexual preference of adults.

A human study showing more methylmercury and lower selenium levels were associated with lower fertility rates (hey, just like the bird study above! crazy, right?):

Associations of environmental exposures to methylmercury and selenium with female infertility: A case-control study

BACKGROUND: Methylmercury exposure is a common health risk resulting from daily fish intake. However, studies addressing the link between methylmercury and infertility are limited and also inconsistent. In addition, no previous epidemiological studies have accounted for the interaction between methylmercury and selenium. We aimed to investigate the association between environmental exposures to metals and female fertility.

[...]
RESULTS: The mean selenium level in blood (± SD) and the selenium/mercury molar ratio were significantly lower in the infertile group (189 ± 25 μg/L and 94.6 ± 44.3, respectively) than in the control group (200 ± 25 μg/L and 118.4 ± 70.5). By contrast, blood mercury levels after adjusting for blood selenium and age were significantly higher in the infertile group than in the control group. Multiple logistic regression analyses with the adjustment for the other metals and potential confounders confirmed significant associations of infertility with elevated mercury and reduced selenium levels. No significant correlations were observed between anti-Müllerian hormone and metals.

CONCLUSIONS: Methylmercury and selenium exposures appear to have adverse and protective effects on female fertility, respectively. This is the first report to suggest the antagonistic interaction between methylmercury and selenium in relation to human female fertility.

So maybe one should figure out their selenium level, in order to protect themselves against however much methylmercury they are or aren't getting. I do this with my Testing & Consultation clients every day.

It's in the lake fish too, folks:

Estimated exposure to mercury from fish consumption among women anglers of childbearing age in the Great Lakes region

We studied the fish-eating habits of WCBA who had a fishing license and lived near the Great Lakes, where mercury in locally-caught fish is a concern, as these women were likely at greater risk of elevated mercury exposure than the general population.

If you eat fish and shellfish, you ARE eating methylmercury.  It is in ALL the fish and shellfish, it is only the degree/content that varies.  I personally choose to avoid a guaranteed dose of this neurotoxin...so no, I don't eat fish or shellfish.

Conclusions

The takeaways:

• If you are eating fish or shellfish, seawater or saltwater, you are GUARANTEED to be eating some amount of methylmercury.
• Cadmium accompanies mercury in fish and shellfish, based on my hair mineral analysis observations over years.
• Methylmercury is bad for fertility, in birds and humans.
• If you were hoping (or planning) that the selenium in fish or shellfish would protect you from the mercury (what about the cadmium though?), wouldn't it be smart to make sure you had enough?  This is easy for me to assess via a hair mineral analysis.
• Mercury from dental fillings does NOT show up on a hair test.  That requires a blood test or a urine test.  Silver/amalgam/mercury fillings are nearly always better OUT than IN.  If you want to get yours removed, I would suggest finding a dentist who has been trained through https://iaomt.org/ to get it out in the least "toxic-to-you" way.