framcosco, my experience has actually been the exact opposite. Whenever I get in wild polys, I'll drop a few pellets into their bag or bucket during acclimatization. They gobble them right up. Most CB I've brought in have been difficult to feed at first, not even taking bloodworm or mysis except for after lights out.
Interesting, maybe I just need to own more bichirs. Although Ben makes an interesting point that both cb & wc have the same instincts.... maybe what I have observed is more so species contingent? For example all three wc adult mokes I own took considerably longer to eat than my other bichirs.
Some polys have better WC colorations while some is nicer if CB. But they are both about the same i feel. Just remember WC ones might have bichir worms!
Personally I don't think there are really much difference between a WC and a CB. But with WC, there is a much higher chance of them having bichir worms, nevertheless you are expected to deworm all bichirs before introducing them into your aquarium regardless of whether they are WC or CB.
I have noticed a difference with some species. My retros took the longest to start taking food regularly. Sens and dels were eating in the bag. Ornate and laps settled quickly as well. It may also have something to do with the tank setup. My tanks are very heavily planted with lots of driftwood, so they seem really relaxed. Seeing one of my polys startle is a very rare event. Of course, I have three young kids running amok through the tank as well, so that might have something to do with it.