Use of coelomic fluid as a noninvasive indicator of reproductive status in elasmobranchs

Abstract

Information on reproduction in elasmobranchs is important for the management and conservation of populations. However, the ability to obtain reliable data on elasmobranch reproduction without animal euthanasia is extremely limited. Therefore, there has been a call for nonlethal approaches for identifying reproductive status of elasmobranchs. Although useful, current techniques can be limited with respect to access to equipment and reliability of blood analyses. This study investigates whether a new noninvasive approach, the examination of coelomic fluid (CF), can provide a reliable indicator of reproductive status. CF is fluid that bathes the internal organs of the abdominal cavity, including ovaries, and can be sampled noninvasively through a catheter. Recent studies on CF have demonstrated the presence of yolk platelets in the fluid, a specific indicator of follicular development. This suggests that CF may provide a more detailed representation of reproductive state than other nonlethal approaches, such as plasma hormone levels. Thus, we examined CF collected from bonnethead sharks (Sphyrna tiburo), which serve as model elasmobranchs for this work due to their well-described pattern of reproduction, abundance, and easily accessible coelomic pores. We examined differences in gonadal steroid hormone concentrations and protein content in CF in relation to reproductive stage, as well as in comparison to variations in plasma gonadal steroid concentrations. To understand more about the structure and role of the poorly studied coelomic pore system, we also examined the cellular architecture of these structures in relation to sexual activity