Abstract

Elasmobranch fish are popular aquatic animals commonly found in zoo and aquarium collections. With a dramatic range of shapes, sizes, and nutritional needs, discerning nutritional status in sharks and rays can be challenging, with weight trends, plasma chemistry, and ultrasonographic assessment of hepatic indices providing some of the only true objective data regarding nutritional condition. Energy metabolism in elasmobranch fish is unique, yet still features many factors (including plasma analytes cholesterol and triglyceride) that have been widely explored in mammalian and avian species. Generally, elasmobranch fish have lower cholesterol levels than other taxa and demonstrate a higher reliance on β-hydroxybutyrate and ketosis for energy mobilization.^1,2,3 However, cholesterol (CHOL), its constituent lipoprotein components (HDL, LDL, VLDL), and triglyceride (TRI) have been measured across a number of elasmobranch species, both wild and in managed care. Accounting for species-variability, various studies have established correlations for some of these analytes as indicators of nutritional status (tiger, nurse, and blacktip sharks),^4,5 stress and trauma (cownose rays),⁶ and reproductive status (Brazilian guitarfish, small-spotted catsharks)^7,8. Historically, measurement of these parameters required an outside reference laboratory and demanded significant sample sizes for testing. Over the past few decades, the development of point-of-care analyzers, including for nutritional analytes, has progressed. Portable, inexpensive, and often using smaller samples than required for traditional lab testing, these analyzers have been scrutinized by biologists working in challenging field conditions or with species whose small size precludes non-lethal sampling for particular analytes. CardioCheck® Plus is a point-of-care analyzer that is approved by the FDA for human use and provides direct measures for glucose, triglyceride, and cholesterol lipoproteins off a 20-uL sample of whole blood.

Over a two-year period, blood samples were collected from healthy elasmobranchs within a public aquarium collection during the course of routine examination. Among other diagnostics, plasma samples were submitted to an outside lab for chemistry and paired; 20-uL whole blood samples were processed on the CardioChek® Plus. The upper and lower detection thresholds of the CardioChek® Plus were limited relative to diagnostic lab testing, and the samples for three species of sharks tested were below detectable limits using that method. However, across four stingray species, 41 samples were available for comparison. Between the two testing modalities, there was good correlation, but poor agreement for glucose, cholesterol, and triglycerides, with both glucose and cholesterol showing a constant bias. This is similar to findings published in other exotic species, including Amazon parrots⁹ and chickens¹⁰. While not valid for clinical use at this time, more targeted sampling and use of more specific comparison tests, such as cholesterol electrophoresis, may allow development of species-specific correction factors that would make the CardioChek® Plus a useful tool for clinical nutritional assessment in elasmobranchs.

*Presenting author

Literature Cited

1.  Babin P, Vernier J. Plasma-Lipoproteins in fish. J Lipid Res. 1989;30:467–489.

2.  Speers-Roesch B, Treberg J. The unusual energy metabolism of elasmobranch fishes. Comp Biochem Physiol Part A Mol Integr Physiol. 2009;155.417–34.

3.  Metcalf V, Gemmell N. Fatty acid transport in cartilaginous fish: absence of albumin and possible utilization of lipoproteins. Fish Physiol Biochem. 2005;31:55–64.

4.  Gallagher A, Wagner D, Irschick D, Hammerschlag N. Body condition predicts energy stores in apex predatory sharks. Conserv Physiol. 2014;2:1. https://doi.org/10.1093/conphys/cou022.

5.  Gallagher A, Skubel R, Pethybridge H, Hammerschlag N, Cooke S. Energy metabolism in mobile, wild-sampled sharks inferred by plasma lipids. Conserv Physiol. 2017;5:1. https://doi.org/10.1093/conphys/cox002.

6.  Cray C, Rodriguez M, Field C, et al. Protein and cholesterol electrophoresis of plasma samples from captive cownose ray (Rhinoptera bonasus). J Vet Diagn Invest. 2015;27(6):688–695.

7.  Wosnick N, Daldin Leite R, Giareta E, Morick D, Hauser-Davis R. Unraveling metabolite provisioning to offspring through parental fluids: a case study of the Brazilian guitarfish, Pseudobatos horkelii. Front Physiol. 2022;13. https://doi.org/10.3389/fphys.2022.911617.

8.  Valls E, Navarro J, Barría C, Coll M, Fernández-Borras J, Rotlant G. Ecophysiology of the small-spotted catshark in free-living conditions. Fish Mediterr Env. 2016;14:3.

9.  Barboza T, Beaufrere H. Comparison of a point-of-care cholesterol meter with a reference laboratory analyzer in companion Psittaciformes. J Avian Med Surg. 2019;33:7–14.

10.  Irvine K, Mans C, Friedrichs K. Validation of 2 point-of-care meters for measuring triglycerides in chickens using whole blood and plasma. J Vet Diagn Invest. 2017;30(2):197–204.