Dear Jakub,

The most appropriate suggestion is to dissect the fishes and perform a direct study of the gonads. The main problem is that if the fishes are immature the identification of ovaries and testes can be difficult. I would suggest that you try first dissecting some adults and when you feel confortable with your identifications, you can try dissecting juveniles.

With best wishes,

Gloria

Thank you for your feedback Gloria,

Actually we have finished observation of laminae circularis and measuring of pectoral fins of 0+ males, we also tried identification of haploid cells in gonads of male with the using of flow cytometry.

But your suggestion seems to be a good way to confirm sex of juvenile Cobitids.

Best for you,

Jakub.

 good answer Gloria Arratia