Gonadal variation in Great Lakes sea lamprey, Petromyzon marinus, larvae

The observation of atypical gonads in land-lacked sea lamprey, larvae from several streams tributary to the Great Lakes led to this descriptive study on typical male and female gonads, as well as atypical gonads. Typical male and female gonads examined in the present study have similar characteristics to those observed in the past; however, larvae with atypical gonads have some characteristics of both male and female larvae. Many of the atypical larvae had an unusual number of germ cells, or many atretic oocytes. Based on quantitative evaluation of several gonadal characteristics of male, female and atypical larvae, it was possible to verify atypical status of 88% of the larvae which had been qualitatively assigned the atypical sex. Examination of larvae front 15 different populations suggest the proportion of atypical larvae is currently much higher in streams tributary to the Great Lakes, than was previously observed The slowing of gonadogenesis, or the diversion of energy for somatic development are possible causes of the? atypical gonads observed in this study.