This might be a good starting point: 

Anderson, R.C., Chabaud, A.G., Willmott, S. (eds). 2009. Keys to the Nematode Parasites of Vertebrates.

Yes, there are some resources available.  Some are quite old, particularly those of the group published by Russian authors such as Skjabin, who compiled the work of others up through the 1950s.  Also, you might consider attending the 9th International Symposium on Fish Parasites this summer in Valencia, Spain.  Many experts will be there who can be of great help to you.  I have provided the link to the symposium website below.

http://www.9isfp.com/

Best wishes,

Bruce

Keys to the Nematode Parasites by Anderson et al (eds). 2009. .