The Wild and Wacky World of Fish Reproduction

Yes, it’s true. Sexual reproduction was invented by fish over 380 million years ago, long before dinosaurs roamed Earth. While we can’t see those ancient fish in action, modern descendants like sharks give us clues to the origin of sex: think rough-and-tumble encounters, siblings that eat each other in the womb, and the earliest examples of placentas, which beat mammals to the punch.

But sharks are just the beginning. Across the fish world, sex takes on a dazzling variety of forms. Some fish switch sexes once or multiple times throughout their lives. Others engage in chaotic mass spawning events, while a few opt for lifetime monogamy (with plenty of cheating on the side).

And when it comes to raising the kids? Strategies range from complete abandonment to devoted care, including mouth-brooding, embryo-carrying, and even outsourcing the job to another species. 

About the Speaker:  Dr.Jay Nelson, professor of biology at Towson University, will be our guide into the strange, fascinating, and often hilarious reproductive lives of fish. His research explores how environmental changes, especially those caused by human activity, impact fish physiology and behavior. His work spans from acid rain and ocean acidification to hypoxic dead zones and climate-altered freshwater systems. Jay’s scientific journey began with trout physiology as an undergraduate and led him through international research fellowships in Germany and Canada, where he pioneered techniques for studying individual variation in fish performance. At Towson, he has continued this work with a focus on both native and invasive species, including striped bass and Northern snakehead, and how they respond to challenges like hypoxia, warming, and altered stream flow. He has mentored over 75 research students and conducted fieldwork on four continents. In both his lab and classroom, Jay is passionate about helping students understand, not just memorize, how living systems function in a changing world.