Using Ultrasound and Metabolic Parameters to Assess Energy and Body Condition Stores of Elasmobranchs (Retrospective Study)
Abstract
Body condition is a key element in assessing the health of elasmobranchs and has become a standard in the management of fish for evaluation of their general fitness.1 Researchers have used standardized body size measurements, weights, fatty acid levels, and triglycerides as a proxy to body condition.2 These methods are advantageous because they can be assessed antemortem, however, they require additional validation and some may lack required precision.1 We have developed a method to evaluate liver condition for various elasmobranch species using ultrasonography to measure a liver to spleen ratio (LSR). The method is derived from human lipidosis evaluation which uses liver to kidney echogenic-density comparisons to diagnose disease.3 Elasmobranchs use hepatic lipids to store the majority of their energy reserves and for buoyancy.4 Because the spleen does not store lipids, its echogenic-density is relatively constant regardless of nutritional state and therefore can be used to normalize liver echogenic-density,5 which changes relative to lipid content. The LSR for managed care stingrays was significantly higher than wild stingrays, indicating higher liver echogenic-density. Additionally, osmolality and BUN appear to positively correlate with increasing LSR. Preliminary data suggests ultrasound derived LSR, BUN, and osmolality measures may allow for quantitative antemortem indices of liver and body condition in elasmobranchs. Extension and validation of the technique to include a variety of sharks and ray species in varying body conditions, seasons, health status, and ecological niches is warranted.
Acknowledgements
Very special thanks to the animal hospital and husbandry staff at the The Seas with Nemo and Friends, Walt Disney’s Parks and Resort® and Castaway Cay, Bahamas, Disney’s Animals, Science and Environment, for their excellent care of these animals. Additional thanks to the staff at the Bimini Biological Field Station for capturing wild rays. This study was supported in part by the Bahamas Department of Marine Resources, the National Institute of General Medical Sciences (NIGMS) Grant Number P20GM104932, and COBRE, CORE-NPN, Chemistry Research Core. All research and activities were conducted under IR1805.
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