Perhaps it may be difficult becuase of the conditons necessary. Another thing is how can sex be really differentiated? The size suggestions seems arbitrary since an eel can be over fed or given fortified food which would allow it to increase in size during captivity.
This could be an interesting project. Of course tons of research need to be done, but it is my inclination to think that most things are already out there, it is just a matter of accumulating data. Some of the things I would imagine are necessary to know is specific details of locations in which they are found. Weather and seasonal indicators, possible description of the bodies of water they inhabit. Even local information from fisherman, such as what time of the year they seem to catch the most younglings or what else is going on around them when they do catch the most visibly young specimens, so forth and so on. Questions, questions, questions...
Any takers?