Influence of Substrate and Salinity on Air-Incubated Gulf Killifish Embryos

Gulf killifish Fundulus grandis have evolved the ability to utilize air incubation in marsh grass to protect embryos from aquatic predators and allow for synchronous hatching during the following diurnal peak tide. This incubation strategy provides a humid, oxygen-rich environment for the embryos to develop. The current project investigated practical materials that could be used in an aquaculture setting to mimic the air incubation strategy at different salinities, and determined the effect of substrate (moistened with 7.5-g/L salinity water) on embryo size after an extended incubation period (19 d) at 22°C. Air-incubated embryos were placed on synthetic foam, bamboo batting, or burlap cloth substrates. Substrates were moistened with 3.5-, 7.5-, 14-, 20-, or 27-g/L-salinity water, and hatching was induced by submersion in water after 19 d of incubation. Embryos incubated in water (3.5- and 7.5-g/L salinity) at the same temperature began hatching at 8 d and continued intermittently until 14 d. These water-incubated embryos had a hatch rate (mean ± SE) of 44.2 ± 1.1% in 3.5-g/L-salinity water and 49.1 ± 0.5% in 7.5-g/L-salinity water. The percentage of air-incubated embryos that hatched was significantly affected by both substrate and salinity. For all air incubation substrates, the 7.5-g/L salinity treatment provided the numerically highest overall percentage of hatched embryos, 69.9 ± 3.6%, 69.9 ± 6.5%, and 73.8 ± 4.6% hatching on foam, bamboo, and burlap, respectively. Overall, the foam substrate had the highest hatch rate among salinity treatments. Embryo size at hatch was assessed at the 7.5-g/L salinity for water and all air incubation substrates. The air-incubated larvae were found to be significantly larger than their water-incubated counterparts, and foam-incubated larvae had the smallest abdominal area. Air incubation of Gulf killifish eggs on foam substrate can be used as a production tool to produce larvae that can be synchronously hatched after an extended incubation period.