Seasonal and Tidally Driven Reproductive Patterns in the Saltmarsh Topminnow, Fundulus jenkinsi

Fundulus jenkinsi is recognized federally and within a number of northern Gulf of Mexico states as a Species of Concern. Little is known about its life history, but a detailed reproductive histology study of F. jenkinsi can provide the foundation needed to quantify reproductive parameters in this rare species in need of conservation. Monthly gonadosomatic index (GSI) of male and female F. jenkinsi indicated a spawning season from April through August. However, ovarian histological analysis suggested March through August was a more accurate spawning season. The multiple oocyte stages within F. jenkinsi in the spawning capable reproductive phase indicates batch spawning, similar to other members of its family. Many estuarine members of the family Fundulidae exhibit a semilunar spawning pattern, yet the oocyte composition of ovaries of F. jenkinsi suggested spawns occur multiple days around the time of spring tides both within a population and on the individual level. Spawning did not occur on neap tides, and no late secondary growth vitellogenic oocytes (SGl) were found in the majority of females captured during neap tide. The lack of SGl oocytes in females during the spawning season suggests the necessity for establishing a new sub-phase within the spawning capable phase, termed the redeveloping sub-phase. This new sub-phase is applicable to other batch spawning species with group synchronous oocyte development. This work contributes to a better understanding of the importance of intertidal saltmarsh habitat to F. jenkinsi, as spawning intensity appears to increase with tidal height and marsh inundation.