You can follow this paper to get some information which will be helpful for you.

http://www.infish.com.pl/wydawnictwo/Archives/Fasc/work_pdf/Vol13Fasc2/Vol13fasc2%20-%20w05.pdf

interesting one. the freshwater fishes have rough pectoral fins. i live in inland areas and cannot get the mature eels but usually the cloacal area of males is swollen and larger than that of the females. i would like to confirm though.

Hi, Elizabeth! What age was the fish then? And how big was it?

You can check these papers -

http://onlinelibrary.wiley.com/doi/10.1111/j.1469-7998.1966.tb03012.x/abstract

http://link.springer.com/article/10.1023%2FA%3A1007575600789

http://www.ncbi.nlm.nih.gov/pubmed/6661926

Cheers

I have specimens from a wide range of size and age. And still sampling more individuals. Thanks alot for the papers i will check them out. 

Hi!

how big is the eel? It is possible that it may still be undifferentiated. The male gonads have some sort of lobes (however they will be very poorly developed even at the silver stage) while the female gonad looks more like a ribbon and is easier to identify.

"[...] body length > 55 cm, indicating that they were all females according to the distinct length dependent sex dimorphism (Tesch, 2003)."

Stein et al (in press): Downstream migration of the European eel (Anguilla anguilla) in the Elbe River, Germany: movement patterns and the potential impact of environmental factors. River Research and Applications

thank you very much for the answers

Hello Elisabeth, length-weight versus sex should be carefully considered, according to environmental conditions. You can find my study here: http://amsdottorato.unibo.it/4788/

Dear Elizabeth,

I hope the attached papers would be helpful for you.

Shahram