Abstract Gulf killifish Fundulus grandis show promise for commercial development as a baitfish species marketed to anglers on the U.S. Gulf Coast. Additionally, fishes in the genus Fundulus are increasingly cultured as model organisms for various fields of scientific inquiry. Research examining effects of maternal body size on reproduction in this genus and more generally in fractional spawning species with eggs capable of terrestrial development is lacking. The present study assessed the effects of female body size on reproductive investment in laboratory held Gulf killifish as well as subsequent implications for larvae. Larger females had significantly higher fecundity and produced individual eggs of greater volume. Gonadosomatic index more than doubled as female body mass increased from 6.9 to 12.9g, but did not increase significantly in females of body mass>12.9g. Larger eggs required significantly longer incubation periods, and newly hatched larvae from larger eggs had more endogenous nutritional resources but shorter body length. Experimental results describe maternal effects in a fractional spawning species producing eggs with the ability to incubate terrestrially. Results also provide practically useful information for aquaculturists as F. grandis are increasingly cultured commercially and in laboratory settings.