The following data come from a study on the effects of sperm competition and cryptic female choice as putative postmating barriers in two lamprey ecotypes (Lampetra planeri and L. fluviatilis) with a partial reproductive isolation. We measured sperm traits in both ecotypes and designed sperm competition experiments to test the occurrence of cryptic female choice. Sperm competition experiments either at equal semen volume or equal sperm number were realized to investigate the role of sperm velocity on fertilization success.

All the data were collected in April and May 2021 in France.

Adult lampreys were caught in the river by electrofishing in the Oir River (France). In the following days, sperm traits were assessed. Sperm number was assessed using a Thomas cell counting chamber and sperm velocity was measured by using a Computer-assisted Sperm Analysis System. 

Then in vitro fertilizations were realized among and between ecotypes.