A histological study of seasonal ovarian development in freshwater drum in the Red Lakes, Minnesota

Female freshwater drum Aplodinotus grunniens Rafinesque, from the Red Lakes of north central Minnesota, U.S.A. were sampled periodically over a 13‐month period. Red Lakes drum mature at approximately age 9 and can live to be over 60 years old. The ovarian development of drum from its northern limit of distribution is described histologically. The stages of oocyte growth and the seasonal change in the proportion of oocyte stages within the ovaries are presented. Drum ovaries contained a continuum of oocyte sizes and at spawning, only the largest oocytes are ovulated. A large percentage of the oocytes became atretic mid‐way through the spawning season, while gonadosomatic indexes were still high. This may have reduced the spawning potential of Red Lakes drum.