Tony,
Good luck with the fishing. I would suggest thatif you catch eels in the saltwater, (typically in the summer) they will be better than the fresh water ones, (same fish different environment).
However if you catch eels in a lake or river it is always a good idea to keep them alive in fresh water for a few days to get rid of any muddyness. For the Avon it is probably not necessary, but just thought I'd mention it.
Incidentally I would do the same with the Crays and purge them for about 2 weeks. change the water at least once a day and an air pump is always handy to keep them alive although they will climb up the tube and "migrate aruond the garage. I catch them on a mates river and we often get upto 300 in a couple of hours. It's a lot of shelling for a small return!!
Rgds,
FB