The most massive teleost, the ocean sunfish(Mola mola), is an order of magnitude smaller than the largest cartilaginous fish,the whale shark (Rhincodon typus), and issignificantly smaller than several other extantelasmobranch species. Possible reasons for this discrepancy in maximum size include:anatomical, physiological, ecological, and life-history/ontogenetic constraints. Weexamined life-history traits and growth ratesas the most likely constraints on maximum teleostsize. For pelagic fishes there appear to be two life-history strategies: producing few,large, live young or many, tiny eggs. We propose that this dichotomy is an evolutionaryvestige of the freshwater origins of teleosts, and is the basis of the limitation onmaximal body size in teleosts.