PARENTI, L.R. *; GRIER, H.J.; National Museum of Natural History, Smithsonian Institution, Washington, DC; Stock Enhancement Research Facility, Florida Marine Research Institute, Port Manatee: Evolution and Phylogeny of Gonad Morphology in Bony Fishes

Gonad morphology at the gross anatomical or histological levels has long been studied to identify annual reproductive cycles and length of breeding season, among other goals. Comparative surveys across vertebrate taxa have not been detailed enough, however, 1) to describe fully the differences and similarities between gonads of bony fishes and other vertebrates, and 2) to use gonad morphology in phylogenetic analyses. These are our aims. First, an emerging constant among vertebrates is the similar morphology of the germinal epithelium. All osteichthyans have a germinal epithelium composed of somatic and germ cells in male and female gonads. Activity within the germinal epithelium allows us to understand why lower vertebrates have indeterminate fecundity whereas higher vertebrates do not: in mammals and birds, the germinal epithelium produces oocytes only during embryonic development, whereas in fishes the germinal epithelium produces oocytes throughout the reproductive life of a female. Second, we present examples at higher and lower taxonomic levels, focusing on model organisms, of the relationship between gonad morphology and phylogeny. For example, lower teleosts have an anastomosing tubular testis which we identify as primitive for bony fishes; whereas higher teleosts, such as the medaka, Oryzias latipes have a derived lobular testis. Further, atherinomorph fishes, the medaka and allies, have a unique type of lobular testis and egg morphology correlated with an array of reproductive modifications such as sperm-bundle formation, internal fertilization, embryo retention, and live-bearing. The use of reproductive morphology to identify phylogenetic patterns within bony fishes is explored.