Gulf Killifish

Fundulus grandis, the Gulf Killifish, is one of the largest and most euryhaline Fundulus species, native to the Gulf Coast of the United States and Mexico. It tolerates an extraordinary range of salinities — from fresh water through to full-strength seawater — making it one of the most physiologically remarkable killifish species. Males are greenish with faint spotting, while females display banded colouration. The species is widely used as bait fish along the Gulf Coast.

In the aquarium, F. grandis requires a large tank of at least 120 L given its potential 18 cm adult size. It is an extremely hardy, adaptable fish that accepts a wide range of foods. Water chemistry is very flexible. The species can be kept in fresh, brackish, or marine aquaria. Breeding in captivity is possible with appropriate conditions; eggs hatch in two to three weeks.

F. grandis is a fascinating species for keepers interested in extreme physiological adaptations. Its euryhalinity and large size make it a standout exhibit fish and an excellent subject for educational aquarium displays.

Water: 15–30 °C, pH 6.5–8.5, fresh through full marine salinity — extremely adaptable. Tank: 120 L minimum due to adult size; can be kept in fresh, brackish, or marine setups. Feeding: Voracious omnivore; accepts pellets, flake, frozen, and live foods readily. Breeding: Spawns on substrate or plants; eggs hatch in 2–3 weeks; protect fry from adults. Compatibility: Keep with fish of similar size; will eat small fish and invertebrates.