Yes, tuna and *all fish* for that matter - is problematic due to the Mercury (Hg) content... and it isn't even recommended for pregnant or nursing mothers. Every single food in the Corporate Food Grid is contaminated,
perhaps exceptions are organic meats and farm raised fish.
[The biggest lesson all this is that we will never, ever be sure again what corporate food (human/pet) is not contaminated. The best answer (for me) is to get the heck off the Corporate Food Grid, which IMHO has sunk lower in the same treacherous, interlocked waters as the Corporate Energy Grid, and establish direct ties with local farmers.]
But, the fact remains that right now, many people cannot afford quality organic meats even for themselves, which in my area go for
$21.99 per pound. the US gorwn farm fish is not better priced either. So, packaged tuna likely is a choice in 80% of the people's diet's, and I applaud all those who can manage to purchase human grade tuna instead of pet food tuna for their animals.
(Is it really 80%? Yes, we know that today 20% of people own 85% of the wealth in this country, and 80% of the people get the remaining itty bitty 15% of the wealth. Working the numbers, those 80% are operating below middle class income levels, in the last 6 years. I'd say, the majority of people with families etc. may not be able to afford even good tuna, when the choice between soy-adulterated tuna is $1.25 for 3 oz vs tuna with no soy being around $2.25, guess what they're buying).
That being said, there needs to be some "balance" in the recognition that tuna and all fish have mercury in them: instead of throwing the "baby out with the bathwater", let's take a look at a good analysis of the tuna matter by a very wonderfully informed cat person, and she speaks to what pet owners need to be aware of wrt. tuna.
http://www.felinecrf.org/which_foods.htm#tunaShe ends with this, and I have underlined some words so that her message is not distorted:
As you can see, feeding tuna regularly has some serious health implications for cats. A little tuna occasionally is unlikely to be cause for concern, but I would not recommend feeding it for any length of time or too often. One possible compromise is to add the water in which tuna is packed to your cat's prescription or other diet in order to make it more palatable. See tuna water for more information.
So, if you don't feed your kitty low grade tuna regularly or for any length of time, it is unlikely to be a cause for concern.
Therefore, I feed tuna, which my cat adores, occasionally, as part of a balanced feline diet.