Abstract

Sand tiger sharks, Carcharias taurus, are the most common large sharks displayed in public aquariums. In the wild, female sand tigers mature at 9-10 years of age while males reach maturity in 6-7 years.¹ Estimates of longevity for wild sharks are 16-17 years.¹ Exhibit sand tigers often live in captivity for 10-15 years with survival times reported well over 20 years after capture.² With sand tigers routinely reaching geriatric ages while on exhibit, it would be expected for such animals to eventually show systemic problems associated with aging related organ failure. A review of sand tiger mortality records from two large captive populations revealed kidney problems in six mortalities over a twelve year period. Four of the cases involved primary nephritis and in two cases nephritis was detected as part of other serious clinical problems and was deemed to be secondary in nature. In all of the cases, plasma phosphorous levels were markedly elevated and the phosphorous concentration increase correlated with the degree of kidney involvement and the prognosis. Normal plasma levels established for the two populations of sand tigers were as follows: calcium: 13.2-16 mg/dl, phosphorous 5.1-7.5 mg/dl. All of the primary nephritis cases were in male sharks. One male developed nephritis secondary to a case of peritonitis and a female sand tiger developed nephritis secondary to chronic granulomatous endometritis. Nephritis in sharks manifested itself either acutely with a rapid onset of depression and disorientation followed shortly by death or in a chronic form with the animal gradually becoming debilitated and moribund. Animals with primary nephritis characteristically exhibited the acute form and those with nephritis secondary to or concurrent with other disease processes followed a more chronic course. In acute nephritis, phosphorous levels as high as 22 mg/dl were noted when the shark first showed clinical signs. In the chronic form, initial phosphorous levels were within the normal range but gradually rose to as high as 18 mg/dl as the shark became moribund. Tissue samples revealed a variety of acute and chronic histological lesions. Lesions involved glomeruli as well as tubular and peritubular components of the nephrons. Membranous glomerulonephritis, tubular necrosis and fibrosis, and interstitial inflammation with fibrosis were commonly seen in tissue samples taken from affected sharks. One male shark had a 2 cm diameter nephrolith in its renal pelvis.

Acknowledgements

The authors would like to thank the aquarists at the Ripley's aquariums for their professional support in handling the large number of animals involved in this project.

References

1.  Goldman K, Branstetter S, Musick J 2006. A re-examination of the age and growth of sand tiger sharks, Carcharias tuarus, in the Western North Atlantic: the importance of ageing protocols and use of multiple back-calculation techniques. Environmental Biology of Fishes 77: 241-252.

2.  Mohan PJ, Clark ST, Schmid TH. 2004. Age and growth of captive sharks. In Smith M, Warmolts DI, Thoney DA & Hueter RE (eds).Elasmobranch Husbandry Manual: Captive Care of Sharks, Rays, and their Relatives, Ch. 15, pp. 201-226; Ohio Biological Survey, Inc. Columbus, Ohio.