We investigated semen quality and seasonal changes in serum testosterone (T) concentrations in a male false killer whale, Pseudorca crassidens, under managed care. Semen was collected 107 times in 27 sessions for 22 months between June 2018 and April 2020 and analyzed for semen volume, sperm concentration, total motility, progressive motility, viability, and kinetic rating. Serum T concentrations in blood samples were measured by fluorescence immunoassay 1–4 times a month for routine health assessments from April 2016 to May 2022. The fourth and fifth ejaculates of each session were typically lower in volume but had higher values for all other tested parameters. The monthly mean serum T concentration showed a seasonal change; it began to increase in September, peaked between November and January (i.e., fall to spring), and declined until August (i.e., in late summer). This is the first report on semen quality in false killer whales, where we observed seasonal changes in T concentrations and established that the fourth and fifth ejaculates of a session yielded good-quality semen.

Published online 6 December, 2024; Print publication 31 January, 2025