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Good question.
Page 15 of this advisory report will give you all the information you need about fish from the D&R canal.
http://www.state.nj.us/dep/dsr/2012-advisory-report.pdf
It looks like you should be fine with less than one meal per month if you're not a high risk individual.
Unfortunately, methyl mercury is ubiquitous here in New Jersey. The fish that have the highest levels of mercury and PCBs are the predators that live a long time and eat a lot of fish like bass and pickerel. Those toxins are trapped in small fish and passed up the food chain. The predators multiply the background levels of mercury thousands of times by eating hundreds of small fish in their lifetime.
I caused some controversy on the New Jersey Hunter forum a few years back when some guy was showing off pictures of all the Largemouth Bass he was taking home and feeding to his kids. I told him that those bass contained high levels of mercury and children, with their developing neurological systems, are far more sensitive to mercury contamination than adults. I told him that it was unethical to feed Largemouth bass to children because they can't understand the decision that is being made for them.
