Date Awarded


Document Type


Degree Name

Doctor of Philosophy (Ph.D.)


Virginia Institute of Marine Science


The reproductive and feeding biology of five syngnathid species of the western Atlantic were studied: the pipefishes Syngnathus fuscus, S. floridae, the lined seahorse Hippocampus erectus of Chesapeake Bay; and the pipefishes S. folletti and Oostethus lineatus, from southern and southeast Brazil, respectively. Male syngnathids incubate eggs received from females in a ventral brood pouch, females do not play any additional role in parental care after mating. This natural sex role reversal is a unique characteristic that all male syngnathids have. In other fishes, parental care is usually a female prerogative. Most pipefishes are polygamous, while seahorses are monogamous. Syngnathus fuscus, S. floridae, and H. erectus have a protracted mating period from May through September in Chesapeake Bay, which varies with environmental conditions and eelgrass biomass. Female S. fuscus are dimorphic, gravid individuals undergo morphological and morphometric adaptations for mating. Female S. floridae and H. erectus are monomorphic. In both, S. fuscus and S. floridae, total sex ratio was skewed toward females, but the operational sex ratio was skewed toward males. Total and operational sex ratio in H. erectus were skewed toward females. In female S. fuscus (123 to 255 mm TL), fecundity was from 101 to 1,643 oocytes, whereas in males (83 to 189 mm TL) fertility was from 22 to 870 eggs/embryos. In female S. floridae (116 to 189 mm TL), fecundity was from 38 to 818 oocytes, whereas in males (91 to 176 mm TL) fertility was from 15 to 820 eggs/embryos. In female H. erectus (60 to 123 mm TL), fecundity varied from 90 to 1,313 oocytes, and in males (80 to 126 mm TL) fertility varied from 97 to 1,552 eggs/embryos. Mating period was not defined for S. folletti. Total sex ratio in this pipefish was skewed toward females, but the operational sex ratio was skewed toward males. Fecundity in females varied from 30 to 219 oocytes, and fertility measured for male brood pouches was from 26 to 181 eggs/embryos. Mating period was not defined for the estuarine and freshwater populations of the opossum pipefish, O. lineatus. Male opossum pipefish develop different coloration in the snout. In both populations, total sex ratio and operational sex ratio were not significantly different from the expected 1:1 ratio. In the estuarine population, fertility varied from 49 to 508 eggs/embryos (males from 101 to 165 mm TL), and in the freshwater population fertility varied from 280 to 897 eggs/embryos (males from 119 to 508 mm TL). Excepting O. lineatus, females in other pipefish species appear to limit males reproductive success. In the seahorse H. erectus, most females do not have the chance to find a mate inside Chesapeake Bay. In all syngnathids, snout size and width limit predation to small size prey. Syngnathus fuscus and H. erectus fed mainly on amphipods (Gammarus mucronatus, Ampithoe longimana, and Caprella penantis). Syngnathus floridae fed mainly on grass shrimps (Palaemonetes pugio and P. vulnaris). Southern pipefish fed predominantly on copepods. The estuarine population of O. lineatus fed more on stoneflies, whereas the freshwater population fed more on mayflies.&\sp*& ftn&\sp*&Originally published in DAI vol. 56. no. 3. Reprinted here with corrected text.



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