Parasites of marine mammals are of significant interest in the fields of evolutionary biology, veterinary medicine, human health, conservation, and ecology. Therefore, every opportunity to study them should be seized. This study aimed to report on specimens of cestodes found in the small intestine of a gray whale (Eschrichtius robustus) in Chukotka, Russia, in 2024. The specimens were examined using light and scanning electron microscopy, histology, and molecular analysis. Based on their morphology and host specificity, the cestodes were identified as Priapocephalus eschrichtii. Analyses of the 18S and 28S ribosomal RNA genes confirmed a close relationship between P. eschrichtii and species of Tetrabothrius, which infect seabirds and whales. Sequences of the 18S, 28S, ITS2 rDNA, and gene CoxI mtDNA are reported here for the first time. More than 50 specimens of P. eschrichtii were detected in 1 meter of intestine of the whale with a maximum length of 50 cm. Chronic lymphoplasmacytic inflammation of the intestinal mucosa was observed in the infected whale. The eggs of the cestodes were clustered within an irregular membrane, which may contribute to multiple infestations of the host and lead to diseases that affect the whale’s health and survival. This study should be continued.

Killer whales (Orcinus orca Linnaeus, 1758) are of major interest to scientists and society in general as apex predators and intelligent marine mammals. Despite the world’s practice of keeping some of them in sea pens (not indoor pools), nothing has been published about their blood analytes in such conditions. We aimed to fill this gap and provide data for 10 young killer whales. They were legally captured for sale, kept in sea pens in the Sea of Japan from July 2018 to August 2019, and then released back to the wild under the public pressure. These killer whales were under the care of veterinarians throughout this time, and blood samples were taken regularly. The animals were clinically healthy. We have retrospectively analyzed variations in the blood analytes due to different influencing factors. We have found effects of water temperature, period of adaptation to captivity (related to stress), and individuality on their blood analytes. No statistically significant correlation between killer whales’ sex and their blood analytes has been found. The results of our study contribute to a broader understanding of the killer whales’ physiology. Veterinarians can apply them to diagnose and manage health problems in these unique animals more accurately in order to increase chances of recovery.