One of the most abundant and, in my opinion, unappreciated groups of fish swimming around the great tidal waters of New York Harbor has to be small and slender Killifish or killies for short.
There is nothing impressive about their looks, appearing like shy, little minnow-like fish with a single dorsal fin and a tail that is squared or rounded in shape. Their teeth are not as sharp as snappers nor do they move as fast as stripers. They are also not as slimy as eels or as prehistoric as sturgeon.
Yet, look within a Peterson Field Guide about Atlantic Coast Fishes and you will find a wide assortment of killie species under the Cyprinodontidae family, from Diamond killifish to Rainwater killifish. New York Harbor and surrounding local waters support a wide assortment of killies too, including Banded killifish and Spotfin killifish, but the two most commonly found species in my opinion are Striped killifish and Mummichogs. I constantly find these fish in my seine net.
Early Dutch settlers in northeast America provided the name Killifish. The name "killi" comes from the Dutch word “Kil” meaning “creek.” Killies are essentially "fish from the creek.” In New York State, places like Arthur Kill, Fishkill, or Kill Van Kull have actually nothing to do with murder, but everything to do with fish and a well-established Dutch word.
The name mummichog is derived from Native American people in New England, possibly a Narragansett term meaning "going in crowds.” This illustrates their ability to be a large schooling fish.
Anglers frequently use these fish as bait, since just about anything bigger or stronger will eat a killie, including striped bass, sea bass, bluefish, eels, and a variety of wading birds from Great Blue herons to Great egrets.
There are more to this fish than just bait though. KIllies are one of the hardiest fish on Earth.
Killifish have the remarkable ability to endure various extremes of temperature, salinity, and even oxygen levels down to nearly zero. Believe it or not, I have seen fishermen hold live killies out of water for hours in their pants or shirt pocket to be saved later, flipping and flopping around, for live bait. As long their gills are kept moist, killifish can survive, albeit I’m sure uncomfortably, for several hours out of water.
This amazing ability to tolerate extreme conditions and difficult environmental circumstances has made them popular “test rats” in scientific studies of toxicology, not just on this planet, but also in outer space. Killifish were the first-ever fish sent into space in 1973 aboard Skylab, the United States' first space station, which orbited Earth from 1973 to 1979. Killies were used in a scientific experiment to see how zero gravity in outer space would affect fish. Due to the lack of gravity, the fish had a hard time finding which way was up or down while swimming. Fish don’t make good astronauts.
Yet, due to their durability and knack to live in very foul or polluted water, killies are the poster-child or poster-fish for urban-suburban waters. In the very polluted days from the 1950s through the 1980s when New York Harbor and its tributaries were largely oxygen-deprived due to excessive amounts of raw sewage and other pollutants entering waterways, killifish could be found not only existing but thriving. Large schools of killies provided much needed nourishment to bigger fish and wading birds when not much food could otherwise be found.
Killifish helped sustain life and return biodiversity to New York Harbor. Strong schools of killies provided the nutrients necessary for larger fish and wading birds to feed. In doing so, the fish provided food and energy indirectly to top predators, such as ospreys, terns, and other fish-eating birds.
Killies are a crucial piece in a coastal food web. During the spring, summer and fall, you can find many fish and wildlife foraging for killies, while killies, which are opportunistic feeders, will help control a variety of species, including algae, insects and insect larvae, worms, small crustaceans and mollusks, other fish and even carrion. According to the Chesapeake Bay program, killies are able to consume up to 2,000 mosquito larvae in a single day and have been introduced to ponds and ditches as a natural method of mosquito control.
Slim, shallow waterways hold a special place for these fish. Soon they will be swimming upstream to spend the winter in a more or less sluggish state on the bottoms of creeks or streams. If winter conditions are harsh, the fish will bury themselves several inches into the mud to escape being covered by sharp ice. Resilient fish indeed.
Unlike other fish that will migrate out of the estuary for the winter, there is no evidence to suggest killies ever depart the great tidal waters of New York Harbor. It’s the year-round home for one of the hardiest fish in the world.