A Reappraisal of Reproduction in Anadromous Alewives: Determinate versus Indeterminate Fecundity, Batch Size, and Batch Number

Abstract

Innovative methods for analysis of reproduction may provide more information that can be used to conserve species of concern. We present data on oocyte development, batch size, and batch number of anadromous Alewives Alosa pseudoharengus in a lake-spawning population located in Connecticut. We sampled female Alewives as they arrived at the spawning habitat (uprunners) and females as they were leaving (downrunners). We estimated batch size by weighing all oocytes and performed image analysis on oocytes in subsamples of some ovaries, thereby estimating oocyte size-frequency distribution to define the number of batches. We performed both whole-mount and histological analysis on other ovaries to compare gravimetric and stereological estimates of batch size and to precisely characterize oocyte developmental stages. Uprunners had advanced oocytes at the ultimate stage of vitellogenesis and usually three additional less-developed batches. Postovulatory follicles and oocytes that were being resorbed were prevalent in downrunners but were absent in uprunners. Females spawned at least three batches in a season; however, downrunners had nearly as many batches as uprunners in their ovaries, indicating there was continuing recruitment and maturation of fresh batches. A numerical model of oocyte growth indicated that there is sufficient time for batches recruited at the beginning of the spawning season to develop and be spawned in the same season, indicating that fecundity is indeterminate. Accurate assessments of individual reproductive performance will require detailed consideration of within-season oocyte dynamics as opposed to relying on enumerating oocytes in prespawners.

Received November 25, 2014; accepted July 13, 2015

ACKNOWLEDGMENTS

Funding for field work was provided by the Connecticut Department of Environmental Protection (State Wildlife Grant SWG T-1). Additional support for this project provided in form of a Fulbright Foundation Greece Scholar grant to E.S. We thank personnel of the Connecticut Department of Energy and Environmental Protection (William Hyatt, Rick Jacobson, Steve Gephard, Tim Wildman, and David Ellis) for logistical and data support, and the town of East Lyme, Connecticut, for providing access to the study site. Technical assistance in field and laboratory was provided by John Achilli, Steven Brown, Anthony Ferranti, Steven Hovorka, Ione Jackman, Anna Karina Monteiro, Cody Roberge, Sandra Ruiz, Brian Tate, Joana Vilagrasa, and Anthony Wasley. Karin Limburg and an anonymous reviewer suggested numerous improvements to an earlier submission. This animal research was conducted under University of Connecticut Institutional Animal Care Protocol A04-128.