2.1. Sea cucumbers used in the experiment
It has been recognized that there are three types of body color in
the Japanese common sea cucumber A. japonicus, i.e., green, black
and red types (e.g., Choe and Ohshima, 1961). A recent genetic
study suggested that the red type and the other two types can be differentiated
as species (Kanno et al., 2006). Chang et al. (2009) confirmed
the difference in the genetic structure not only between
Japanese red type and green-black type populations but also among
green-black type populations from China,