Steatitis in Cold-Stunned Kemp's Ridley Sea Turtles (Lepidochelys kempii)

Abstract

The pathogenesis of steatitis that infrequently occurs in cold-stunned Kemp’s ridley sea turtles (KRT; Lepidochelys kempii) has been undetermined. The objectives of this study were to investigate the clinical (n = 23) and histologic findings (n = 11) in cold-stunned KRT, and to compare plasma concentrations of α-tocopherol (vitamin E), thiobarbituric acid reactive substances (TBARS), and the TBARS to vitamin E (T/E) ratio (an assessment of oxidative stress) between cold-stunned KRT with clinically and/or histologically confirmed steatitis (n = 10) and free-ranging KRT (n = 9). None of the cold-stunned turtles had clinically detectable steatitis at admission, and the median number of days to diagnosis of steatitis was 71 (range 33–469). Histologic findings of affected adipose tissue included heterophilic (n = 9) and/or histiocytic (n = 5) steatitis, fat necrosis (n = 7), myonecrosis (n = 2), and intralesional bacteria (n = 6). Cold-stunned KRT had significantly lower plasma vitamin E concentrations (median = 3.5 nmol/g), lower plasma TBARS concentrations (median = 1.6 nmol/g), and higher T/E ratios (median = 0.50), than controls (62.3 nmol/g; 2.1 nmol/g; 0.03, respectively). These results suggest a multifactorial etiology for the development of steatitis in KRT during rehabilitation, including tissue injury, septicemia, and various factors resulting in imbalances of anti-/oxidative status. By highlighting the need to provide more effective vitamin E supplementation, and the need to re-assess specific components of the diet, this study may lead to reduced incidence and improved medical management of steatitis in cold-stunned sea turtles.

Keywords: fat necrosis; hypothermia; lipid peroxidation; oxidative stress; pathogenesis; sea turtle; vitamin E; α-tocopherol.

Figure 1

Gross appearance of steatitis in the right cervical region of a Kemp’s ridley sea turtle (Lepidochelys kempii) during necropsy. Discolored, necrotic adipose tissue is shown. The turtle is in dorsal recumbency with the head to the right of the image.

Figure 2

Transverse computed tomographic studies showing heterogeneous soft tissue density (yellow circled areas) consistent with steatitis in the cranial cervical region (A) and pre-scapular region (B) of two Kemp’s ridley sea turtles (Lepidochelys kempii). (C) The same turtle shown in (B) at approximately the same anatomic location after resolution of disease four months later. Black arrowhead: esophagus, white arrowhead: trachea.

Figure 3

Tissue sections of fat from Kemp’s ridley sea turtles (Lepidochelys kempii) with steatitis. Hematoxylin and eosin. (A) A cluster of bacteria (arrowhead) is present within an area of necrotic fat and degenerate heterophils (asterisks). Hematoxylin and eosin. ×40 objective. Scale bar = 50 µm. (B) Heterophils and macrophages surround necrotic fat (asterisk). A more chronic area of steatitis is present in the lower left as a granuloma composed of multinucleated giant cells formed around ceroid. Hematoxylin and eosin. ×20 objective. Scale bar = 150 µm. (C) A bacterial embolus (arrowhead) is within an area of fat necrosis, hemorrhage, and heterophilic inflammation (asterisks). ×20 objective. Scale bar = 170 µm.

Figure 4

Vitamin E plasma concentrations over time in individual cold-stunned Kemp’s ridley sea turtles (Lepidochelys kempii) with steatitis. The X-axis is days of rehabilitation, and the Y-axis is plasma vitamin E concentrations in nmol/g. * represents the day of diagnosis of steatitis. # represents the day of injectable vitamin E administration for patients that received this treatment (n = 2).

Figure 5

Thiobarbituric acid reactive substances (TBARS) plasma concentrations over time in individual cold-stunned Kemp’s ridley sea turtles (Lepidochelys kempii) with steatitis. The X-axis is days of rehabilitation, and the Y-axis is plasma TBARS concentrations in nmol/g. * represents the day of diagnosis of steatitis.