While derasa's have the reputation of being the easiest, I have recently been having very good luck with crocea's. A few years ago, croceas were less common and had the reputation of being the most difficult. Now it seems that 80-90% of the clams I see sold are crocea's, and it may be that they have become easier through breeding. I've had one for 6 months, another for 3, and both are fully expanded all the time with solid white growth lines on the edge of the shell. I have found that derasa's aren't so much easy as they are fast growing. A small one can triple its size in a few months....but they are very prone to sudden death. One day they are fully expanded and looking vibrant...the next day the mantle has shrunk, the 3rd day they are an empty shell.