Lipid energetics of bullnose rays: Comparison of TAG and FFA concentration in different tissue types

NSF fellow: Xavier Xiong, Carleton College

Mentor: Dr. Christine Bedore

The bullnose ray (Myliobatis freminvillii) is a benthopelagic species commonly found in coastal waters of the Western Atlantic ranging from New York to Central Brazil. Previous physiological studies on lipid content have focused on sharks, and we still know very little about physiology of most ray species, including M. freminvillii. Feeding on mostly hermit crabs and gastropods, bullnose rays are mesopredators (TL=3.23) that affect both upper and lower trophic levels. Studying the energetics of bullnose rays can not only inform fishery management, but also conservations of apex predators that feed on M. freminvillii. In most elasmobranchs, liver acts as the main energetic hub where free fatty acids (FFA) are turned into triacyglycerol (TAG) for storage, and TAG are metabolized into ketone bodies as energetic currency in muscle tissues. Therefore, this study aims to study TAG and FFA concentration in liver, muscle, and plasma. Myliobatis freminvillii (n=7) were caught as bycatch. Colorimetric assays are used to analyze TAG and FFA concentration in liver, plasma, and muscle samples. The linear regressions of liver TAG and FFA concentration against body mass demonstrates there is significant ontogenetic difference in liver lipid content between young of the year and adult rays. Intriguingly, unlike benthic and demersal species of batoids, adult bullnose rays have significantly higher concentrations of TAG and FFA in muscle tissues than in liver. Metabolically demanding feeding behavior and low energy density of the prey items offer a possible explanation for the abnormally high lipid content in bullnose ray muscles.