Biology Seminar: Chessie Craig

Elasmobranch fishes are a subclass of cartilaginous fishes which have a distinct metabolic physiology when compared to other vertebrates. In addition to their different metabolism, elasmobranchs have a unique immune system with reportedly low instances of disease. Elasmobranchs are commonly targeted as sportfish by recreational anglers and caught as bycatch in recreational fisheries. This capture typically involves physical restraint, human handling, and air exposure. When captured and handled elasmobranch fishes enact a stress response that involves the release of stress hormones, and an increase in blood metabolites like glucose, and lactate. Lactate often increases due to the organism entering anaerobic metabolism when they are exposed to air or fight on the line for so long that their oxygen demand exceeds the oxygen they can uptake from their environment. The released stress hormones and blood metabolites are meant to prime the body to cope with the stressor, and in the case of metabolites like glucose, provide skeletal and cardiac muscle with more fuel to meet increased demands. In contrast to other vertebrates, which prefer to use glucose as their primary metabolic fuel source, elasmobranchs have been shown to prefer ketones as a primary fuel source over glucose. The changes in circulating glucose and lactate concentrations in response to stress in elasmobranchs has been well documented, but much less work has been done on ketone concentration changes. It is known that the elasmobranch stress response can be highly variable depending upon multiple abiotic and biotic factors such as sex, age class, water temperature, time on line, and fishing gear type. Therefore it is important to establish an understanding of the stress response of multiple elasmobranch species under a variety of conditions. In this study the blood metabolites glucose, lactate, and ketones (3-hydroxybuteric acid and acetoacetate), as well as metabolic rates, were used to understand how biotic and abiotic factors affect the acute stress response to capture and handling as well as to understand how ketones may contrast in their response to stress with lactate and glucose. This work was conducted on wild caught sand tiger sharks (Carcharias taurus) and laboratory held brown banded bamboo sharks (Chiloscyllium punctatum). The aim of this work is to contribute important data about elasmobranch metabolite changes during stress, the effect of external factors on these metabolite changes, and to investigate the potential role of ketones in the elasmobranch stress response.