Breeding cycle and population survey of euryhaline Syngnathus scovelli in a freshwater portion of Mobile Bay

1. Breeding cycle and population survey of euryhaline Syngnathus scovelli in a freshwater portion of Mobile Bay Bolland, J., Ueda, N., C. Partridge, A. Boettcher Department of Biological Sciences; University of SouthAlabama; Mobile, AL Abstract Population Structure Shortly after the summer temperature peak, the total numbers of individuals collected also peaked with numbers remaining high until temperatures dropped in the winter months (Figure 4). Females were the first to appear in considerable numbers in the spring, followed by males in the summer, then juveniles in late summer (Figure 5). The Gulf pipefish, Syngnathus scovelli, a member of the Syngnathidae family, is the most abundant pipefish found in the coastal regions of the Gulf of Mexico and is the only euryhaline species among the North American pipefish known to enter freshwater areas. Syngnathids, including S. scovelli, exhibit sex-role reversed reproduction with the males brooding the embryos. Relatively little is known about the reproductive cycle of S. scovelli, particularly for those found in low salinity environments. The focus of the current study was to collect population structure and reproductive data for the Gulf pipefish from a low salinity habitat, Meaher Park, located at the mouth of Mobile Bay. Sampling was conducted twice a month from January 2003 to January 2004. The reproductive parameters measured included: sex, gravidity for females, brood stage and brood pouch somatic index for males, and gonadosomatic index as well as hepatosomatic index for both females and males. Population parameters include: length and weight measurements, as well as the general health indicator hematocrit. These reproductive and population parameters will be linked to the environmental parameters. Figure 1. Female (top) and male (bottom). Thegravidfemale is seen with the enlarged trunk, while the male is marked by the presence of the brood pouch (arrow) Figure 7. Mean male BPSI for S. scovelli collected by month for 2003/2004 at Meaher Park. Two collections were performed each month. Error bars indicate + 1 sd. A Figure 2. Pipefish embryonic developmental stages A) Pharyngula, B) Protruding Snout, and C) Juvenile. Figure 4. Total number S. scovelli collected by month for 2003/2004 at Meaher Park. Two collections were performed each month. Introduction Conclusions Members of the family Syngnathidae exhibit a reversal of sex roles. During mating, the female uses a modified anal fin to deposit the unfertilized eggs into a male brood pouch. The male then fertilizes the eggs and carries them through full embryonic development (Vincent et al. 1995). Relatively little is known about the population and breeding cycle of Syngnathus scovelli, particularly in low salinity environments. Work on populations from saltwater environments suggests that, although, S. scovelli can breed year round, the highest levels of reproduction occur during spring and fall and may be linked to water temperature (Hausmann 2001). This work parallels what is known for the northern pipefish, Syngnathus fuscus (Able and Cambell 1998) for which temperature is the primary factor driving the breeding cycle. The objective of the current study was to collect population structure and reproductive data for S. scovelli from a low salinity habitat near the mouth of Mobile Bay. Since members of the Syngnathidae are sex-role reversed, a unique set of reproductive markers based on brood stage of the male are used to characterize the brooding cycle these include the traditional gonadosomatic index (GSI) but also include a brood pouch somatic index (BPSI) (Able and Campbell 1998). • Water temperature appears to be the predominant factor controlling both the appearance of pipefish and their breeding cycle. This is probably linked to changes in density and/or presence/absense of tapegrass, Vallisneria americana, which also cycles with temperature. • Based on GSI and BPSI, males are reproductively active throughout the summer. Peaks in male GSI and BPSI are consistent with the appearance of a large number of juveniles (Figure 5). These events coincide with the higher temperatures that are seen during these periods. B C Figure 5. Number of male, female, and juvenile S. scovelli collected by month for 2003/2004 at Meaher Park. Two collections were performed each month. Laboratory Reproductive Parameters Pipefish were held for less than 24 hours before processing. The fish were anesthetized in 0.008% 3-amino benzoic acid ethyl ester (MS222). The fish were then decapitated and bisected from the uro-genital pore to the site of truncation. The gonads and brood pouch contents were removed for mass measurements. The gonadosomatic index (GSI = [gonad mass (g) / total body mass (g)] x 100), and the brood pouch somatic index (BPSI= [brood pouch mass (g) / total body mass (g)] x 100) were determined (Campbell and Able 1998). Literature Cited Able, W.K., and B.C. Campbell (1998). Life history characteristics of the northern pipefish, Syngnathus fuscus, in Southern New Jersey. Estuaries. 21(3):470-475. Hausmann, J.S. (2001). The relationship between sex roles, sex ratios, and sexual dimorphisms in the mating system of the gulf pipefish, Syngnathus scovelli. Honors Thesis, Amherst College, Amherst, MA. Partridge, C. 2001. The Reproductive Physiology, Biochemistry and Histology of the Gulf Pipefish, Syngnathus scovelli. University of South Alabama MS Thesis. Vincent, A.C.J., A. Berglund, and I. Ahnesjo. (1995). Reproductive ecology of five pipefish species in one eelgrass meadow. Environmental Biology of Fishes. 44:347-361. Reproductive Indicators Male GSI was at the lowest point in the winter, peaked in September, and declined in the subsequent winter months (Figure 6). Male BPSI remained low during late winter and early spring, then increased from early summer to winter (Figure 7). The periods marked by the greatest increase in male GSI and BPSI yielded the greatest number of juveniles (Figure 5). Results Materials and Methods Environmental Conditions The temperature shows a considerable increase in late spring and remains high until winter. During the winter months, the temperature remains relatively low (Figure 3). Salinity and pH show only minor variation over the sampling period. Field Collection Protocol Sampling was conducted twice a month from January, 2003 to January, 2004 at Meaher Park, Baldwin County, AL. A two-person seine was used for collections. Environmental Parameters Temperature, salinity, and pH was determined at the site on each collection day. Field Population and Reproductive Parameters The fish were initially sexed. Males are easily identified by the presence of a brood pouch, which is located ventrally, just anterior to the cloaca (Figure 1). Brood stage of the males was classified into one of four categories, using presence or absence of a brood, and developmental stage of the embryos as a guide (Figure 2). The four categories were: non-brooding, pharygula stage, protruding snout stage, and juvenile stage (Partridge et al. in press). Females were categorized as gravid or non-gravid. Total length of each fish was measured, fish that were greater than or equal to 7.5 cm total length were considered adults, and were transported back to the laboratory for further study. Acknowledgements This research was made possible by funding from AAAS-Merck, ACES-EPA, and UCUR. I would like to thank all those who helped with pipefish collection, maintenance, and feeding: Charlyn Partridge, Christy Gautier, Jason Hermann, Doug Haywick, Jessica Rozelle, and Nobuo Ueda. Figure 6. Mean male GSI for S. scovelli collected by month for 2003/2004 at Meaher Park. Two collections were performed each month. Error bars indicate + 1 sd. Figure 3. Temperature, salinity, and pH measurements by month for 2003/2004 at Meaher Park. Two sets of data were recorded each month.