Three Diaphus species spawned during summer with interspawn periods of 3–9 days.
Females with hydrated ovaries occurred during the daytime in the mesopelagic layer.
Egg size at hydration and batch fecundity was largest and highest in D. watasei.
D. garmani was characterized by maturation at a smaller body size.
D. watasei used greater energy for reproduction as larger-sized mature adults.