This week for Flora and Fauna Friday we have the unkillable Killifish and the fodder of fishermen, the Mummichog or Mud Minnow (Fundulus heteroclitus).
The Mummichog is a member of the Killifish, which used to be one family but is now several. Just know that this group is composed mainly of species of small fish. Our species is indeed small, about the size of a finger. Their scales are the color of our creeks, a murky greenish-brown above, which fades to a beige below. Their bodies are lightly iridescent and often accented down their side by a dozen or more thin silvery lines. Their body is stubby, their fins are round, and their face is blunt and upturned. Mummichog are found in tidal habitats throughout the seaboard of the Eastern United States and are as common as pluffmud in the salt marshes and estuaries of South Carolina. These Mud Minnows can be found along the edge of every creek and tributary on Edisto Island. They are most known for their value as bait fish because not only are they easy to catch but they’re incredibly hardy. Their value as a bait hints at their two most important characteristics. Mummichog are a critical link in the food web of the salt marsh. They are a primary prey item throughout the year for a long list of species including Egrets and Herons, Blue Crabs, Terns, Mink, Kingfishers, and an uncountable number of fish species. The Mummichog themselves feed on small arthropods, detritus, and larval fish.
In fact, Mummichog are world renowned for their ability to survive the harshest of chaotic environmental conditions and have been used widely as a scientific model because of it. I’d even say they top the Mosquitofish in the environmental survival department. Mummichog can survive not only the wild temperature swings of salt marsh shallows but also the anoxic conditions of stagnant wetland pools, the high toxin loads in polluted waterways, and, most impressively, rapid fluctuations in salinity. Salinity in the salt marsh can vary massively. Some shallow areas can become practically freshwater following heavy rains and others near the coast can be close to oceanic saltiness. Salinity plays a critical role in the biology of aquatic organisms. To briefly summarize, freshwater species are constantly trying to keep salt in their bodies and excess water out. Conversely, marine species are continuously pumping water in and salt out. Plop one in the other’s environment and it’s disastrous for their biochemistry. Fish that live in brackish environments, like some areas of the salt marsh, all naturally have a resistance to these fluctuations and some can slowly shift between the two. Mummichog live on the edge, quite literally the edge, or fringes, of the marsh, and as such can experience these shifts in salinity at the drop of a hat, and tolerate them. They have even been known to colonize freshwater ponds as escaped bait.
