Nature Notes: Reign of the Killifish

We are under the spell of a full moon. The tides will run very high. The horseshoe crabs will come into the shallows and breed for the last time. The eggs deposited in the intertidal sands in May will hatch out and a new generation of these prehistoric creatures will have been spawned in one of nature’s greatest and oldest cycles.
    The salt marshes are at their peak of growth now, verdant and shining where not overshadowed by the dreaded phragmites. Cord grass, spike grass, and salt marsh hay are all beginning to flower. Salt marsh fishes come alive when the tide is the highest, the moon shines overhead, and the seawater reaches all the way up to the edge of the forest and on to people’s lawns.
    The killifishes rule at this time. They teem among the inundated marsh grasses and do their thing. That thing is milling about together, ejecting and fertilizing eggs, and otherwise consorting in a night of frenzied reproduction. As the tide recedes, they recede, and as dawn breaks they are all back to normal leading their routine lives like you and me.
    We are relatively rich in killifish species, all of which can be found in any harbor, tidal creek, or lagoon at almost any time of year. They and the silversides in the genus Menidia are a force that drives many of the larger fishes in our estuaries. A few inches long at the most, they are only a step or two above the phytoplankton and seaweeds that form the base of the estuarine food pyramid that ultimately leads all the way up to the big game fish — the sharks and the marine mammals — where the white shark, mako shark, and killer whale are kings. Who could imagine that such a little fish could have such an important role.
    The “kill” of killifish is a word for creek or channel derived from the Dutch “kil.” Many of the streams in and around New York City were called kils by the early Dutch settlers. Some of those local names like Fishkill are still in use and can be found in Hagstrom and Rand-McNally map books covering the tristate area.
    The killifishes were the most common fish in the kills and so the name has stuck and is now almost universal up and down the Atlantic Coast. The near extinct desert pub fish of the Southwestern desert ponds and sloughs is a killifish, closely related to one of ours, the sheephead minnow, which is doing quite well in local marsh waters, especially in spots in the marsh where little ponds form surrounded by spartina grasses that get overwashed by the tides one or two times a day.
    The four most common killies in our area are the mummichog, striped killifish, sheephead minnow, and rainwater killifish, in that order. The mummichog is the only one with a persisting Algonkian name. Obviously, this killifish was common when Native Americans were the only residents on Long Island and in New England and played a role in their everyday sustenance. The mummichog is the killy that will be filling the water spilling onto the marshes during these few nights while the moon waxes fully.
    The striped killifish is a little bit larger and prefers the inlet areas of tidal creeks and harbors where the water can move swiftly on incoming and outgoing tides. It is fusiform like a fighter plane, not chubby and blunt-nosed like the mummichog, which prefers quieter waters. The female has dark stripes running along the side of a whitish body and is larger than the male, which starts out with vertical stripes like those sported by the mummichog.
    The sheephead minnow is the least streamlined of the three, and its shape belies its penchant for very quiet water, where its cryptic coloration affords it greater protection from predators than its swimming speed.
    The rainwater killifish is the smallest of all, barely reaching an inch in length or a little more. It also prefers to live in quiet pools, especially at the top of the marsh where the pools are fresher as a result of rain runoff from land and groundwater intrusion.
    Finally, there is a freshwater killifish, the banded killifish, found in most of our larger freshwater ponds such as Fort Pond in Montauk and Big Fresh Pond in North Sea. Except for its more pointy snout and larger number of vertical stripes, it can be readily confused with the mummichog, which is also vertically banded.
    Most killifishes are good osmoregulators, i.e., they can exist in both saline and fresh waters. One occasionally finds the banded killifish and the mummichog in the same minnow seine catch.
    All of the killifish make wonderful aquarium fish. Why spend a lot of money depleting the reefs of tropical fishes, colorful as they may be, when one can simply go down to the nearest salt creek or tidal lagoon and with a small seine or minnow net on a pole scoop up a dozen or so in less than an hour’s time.