A nonlethal, whole oocyte approach to determining spawn readiness in Pacific sand lance, Ammodytes personatus, in Southeastern Alaska

Abstract

Knowing when a fish spawns is fundamental to understanding and sustainably managing it. The annual reproductive cycle of the iteroparous, total-spawning sand lances and sandeels (Ammodytidae) has been described almost exclusively using gonadal macroscopy and gonadosomatic indices (GSI), with little attention to gamete changes indicative of imminent ovulation and spawning. The latter was the focus of this study, in which spawn readiness of a southeastern Alaska population of Pacific sand lance (Ammodytes personatus) with unknown spawning phenology was assessed using light microscopy of whole oocytes. Oocytes were cannulated from spawning-capable females age-3 to age-9, measured for diameter, and classified into five developmental stages based on the coalescence of lipids and the position and integrity of the germinal vesicle. Oocyte maturation lasted 5-6 weeks, as determined by weekly cannulation of captive females. Diameter and developmental stage of oocytes were more precise metrics of readiness to spawn than macroscopy or GSI and indicated spawning in early- to mid-December. The examination of nonlethally collected whole oocytes is a quick, easy, and low-cost approach to the accurate and reliable assessment of spawn readiness in Pacific sand lance and offers the potential of success with congenerics and other total-spawning fish species.