In-Vivo Ovary Sampling: a New Tool for Predicting Spawn Readiness of Pacific Sand Lance

Pacific sand lance (Ammodytes hexapterus) is one of the most widely distributed and abundant fishes in the nearshore waters of southeastern Alaska. Spawning, however, has not been documented in the region. Because there are no spawning migrations in any species of sand lance, it is likely that spawning occurs near habitat used by adults. It is hypothesized that accurate predictions of imminent spawning in female sand lance will identify temporal windows of opportunity to observe spawning activity in areas of routinely used overwintering habitat. Ovary maturation is similar in most teleost species, with the developing eggs (oocytes) undergoing primary growth, cortical alveoli, vitellogenesis, and final oocyte maturation (FOM). During FOM, the centrally located nucleus migrates to the periphery of the oocyte where it breaks down prior to ovulation. The onset of FOM is indicative of imminent spawning. The duration of FOM, however, is species-specific and unknown for sand lances. In this study, I monitored the initiation and duration of FOM in an overwintering aggregation of sand lance in Juneau, Alaska. A total of 63 adult females were captured and sampled for oocyte maturity; 28 of these fish were held in captivity and iteratively sampled on a weekly basis during November and December of 2010. Whole oocytes (~30) were extracted from anesthetized sand lance by applying gentle suction on a syringed, plastic tube (1.0-mm inner diameter) inserted into the genital vent. Using light microscopy, the fresh oocytes were measured for diameter and staged for maturity. Staging of FOM involved quantifying the distance traveled by the nucleus from the center towards the animal pole, the coalescence of lipid droplets, and the degeneration of the nucleus upon reaching the oocyte periphery. The resultant time-series of oocyte diameter and FOM staging will be developed into a maturity classification system for predicting spawn readiness of in-vivo sampled, wild sand lance.