Mercury levels in shrimp and crab?

I have heard that fish like tuna and salmon should not be fed often because of mercury, but what about shrimp and crab? Should these be fed sparingly as well? I am asking because my picky cats have grown a little tired of the Halo Spot's Stew lamb and have decided to start eating more of the chicken, shrimp, and crab variety of Halo instead.

Tuna, salmon, crab, and shrimp all have mercury.  In fact, salmon, crab, and shrimp all are in the category of the lowest mercury content.  Tuna varies by breed but is usually around moderate mercury levels.

Here is a resource: http://www.nrdc.org/health/effects/mercury/guide.asp   You can find what each category means (exact amount of mercury) by scrolling all the way down.

I'd be surprised if there was much shrimp and crab in the cat food you mention anyway. It'll be mostly chicken I suspect. I wouldn't see that as a big contaminant concern any more than other commercial cat food. Shrimp and crab aren't known for being big heavy metal sources.

Salmon is actually also fine in terms of mercury and other contaminants, as long as it's wild caught. Farmed salmon is known for PCBs so you don't want that. Main issue with getting wild salmon is price!

Tuna is the big no no in this arena, but even then some pet food producers claim to test the fish against the possible contaminants so conceivably it could be ok in that regard. Most people who look into this would tend to avoid tuns though I think.

Other concerns with fish inlcude sustainability; check http://seafoodwatch.org for that sort of info. Also there are some thoughts that fish may worsen urinary crystal formation in some cats. And there are some thoughts that cats fed fish often will come to Want to eat only fish. I'm not sure how proven either of those are.

I've been avoiding fish with my current cats but I may actually back off a bit and let them have some occasionally. I don't worry now about a minor ingredient like a fish oil but I have yet to feed these two anything where fish was a more significant protein.