We have examined the kidneys of 114 animals representing 17 different species of cetaceans (Tursiops truncatus, Stenella coeruleoalba, Stenella attenuata, Stenella longirostris, Peponocephala electra, Globicephalas melas, Globicephala macrorhynchus, Lagenodelphis hosei, Physeter macrocephalus, Kogia sima, Kogia breviceps, Mesoplodon sp., Pseudorca crassidens, Grampus griseus, Delphinus delphis, Ziphius cavirostris, Steno bredanensis) stranding along the Texas and Italian coasts over the last 12 and two years, respectively, and 48 animals of three species taken as accidental by-catch in the eastern tropical Pacific tuna fishery in 2001 and 2002 (S. attenuata, S. longirostris, D. delphis).
The purpose of this study is to describe the normal and pathological aspects of the kidney, and ultimately, to compare kidney diseases of stranded and captive animals. The next step will be to correlate, whenever possible, laboratory analyses to suggest a possible diagnosis.
Several authors have described the anatomy and histology of the cetacean kidney. The kidney is hyperlobulated (with a variable number and size of reniculi between different species). Each reniculus is a miniature typical mammalian kidney with from one to several calyces. The microanatomy is very similar to other mammalian kidneys; the variations are the large size of the "juxtaglomerular macula densa" and the presence of the "sporta perimedularis musculosa."
Lesions of the kidney are not very common or severe compared to diseases in other organs, and usually are not cause of death. However, it is important to know and understand them because they are often associated with other pathology. Another purpose is to determine if the particular urinary system anatomy of cetaceans makes them susceptible to disease.
In the stranded animals we examined, we found several different pathologies. Acute tubular necrosis was nearly universal, and is attributed to agonal or intensely stressful events in the final hours of life. Other findings included the parasite Crassicauda spp; neoplasia (adenoma); amyloidosis; sclerosis and fibrosis of glomeruli; periglomerular capsule fibrosis; inflammation; scars; pyelonephritis; urinary calculi; small abscesses; hyaline nodules probably representing old scars; hydronephrosis; edema; myoglobinuria; cortical hemorrhage; cysts; and an unidentified fungus infection. It appears that the hyperlobulation of the kidney may effectively localize certain processes (i.e., hydronephrosis), while the very small caliber of the calyceal collecting system may make the system prone to obstruction. We did not observe bladder diseases.
This work would not have been possible without the enthusiastic participation of the volunteers of the Texas Marine Mammal Stranding Network, and many other contributing colleagues. This work was supported variously by grants from the National Oceanic and Atmospheric Administration through the National Sea Grant College Program, (NA16RGO457-01) and the Environmental Protection Agency Gulf of Mexico Program (MX822147-01-0), and contract NFFR6000800052, National Marine Fisheries Service. The views expressed herein are those of the authors and do not necessarily reflect the views of NOAA, the EPA, or any of their sub-agencies. This work is also supported by the Centro Studi Cetacei (CSC), and Istituto Centrale per la Ricerca Applicata al Mare (ICRAM), Italy.