Inland silverside
Encyclopedia
The inland silverside, Menidia beryllina, is a neotropical silverside native to eastern North America
, and introduced into California
. It is a fish of estuaries
and freshwater environments.
Inland silversides are quite elongate even for silverside, with lengths 6 to 7 times depth. They have large eyes, a considerably upturned mouth, and a head noticeably flattened on top. Of the two widely separated dorsal fin
s, the anterior fin is small and has 4-5 weak spines, while the posterior fin is larger, with one spine and 8 or 9 rays. The lengthy anal fin is somewhat sickle-shaped, has one spine and 16 to 18 rays. As befits the name, they are silvery on the sides; the back is somewhat yellowish, and the underside is a translucent greenish. These are small fish, with 15 cm recorded, but most adults 10 cm or less.
They primarily feed on zooplankton
, moving in enormous schools capable of depleting populations of the small arthropods and crustaceans they favor. In turn, they are prey for a variety of fish and birds. The silversides congregate in the shallows, generally over sand or gravel bottoms with overhead cover if possible, but then move out to open water in search of additional food, which increases predation risk. They are often observed in a sort of daily migration pattern as a result.
The exact native range of the inland silverside is not known; they are widespread along the Atlantic coast from Maine
to Florida
, and along the Gulf of Mexico
. In the Mississippi River
they can be found in backwaters and reservoirs as far north as Missouri
and Illinois
, hundreds of miles inland.
They were introduced into Clear Lake and the Blue Lakes of California in 1967, in order to control the Clear Lake gnat Chaoborus asticopus and midge
s, and in lakes and reservoirs of Alameda County and Santa Clara County the following year. From there they spread into the San Francisco Bay
and Central Valley, and have since become widespread in central California. In some areas, they are the most abundant fish of any species. Moyle suggests that this fish may have contributed to the demise of the Clear Lake splittail
, although the effect of the silversides' introduction on California ecosystems not been much studied.
Inland Silversides are currently an EPA approved indicator species for acute marine aquatic toxicity testing and short-term chronic toxicity estimating of marine and estuarine organisms.
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
, and introduced into California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
. It is a fish of estuaries
Estuary
An estuary is a partly enclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection to the open sea....
and freshwater environments.
Inland silversides are quite elongate even for silverside, with lengths 6 to 7 times depth. They have large eyes, a considerably upturned mouth, and a head noticeably flattened on top. Of the two widely separated dorsal fin
Dorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
s, the anterior fin is small and has 4-5 weak spines, while the posterior fin is larger, with one spine and 8 or 9 rays. The lengthy anal fin is somewhat sickle-shaped, has one spine and 16 to 18 rays. As befits the name, they are silvery on the sides; the back is somewhat yellowish, and the underside is a translucent greenish. These are small fish, with 15 cm recorded, but most adults 10 cm or less.
They primarily feed on zooplankton
Zooplankton
Zooplankton are heterotrophic plankton. Plankton are organisms drifting in oceans, seas, and bodies of fresh water. The word "zooplankton" is derived from the Greek zoon , meaning "animal", and , meaning "wanderer" or "drifter"...
, moving in enormous schools capable of depleting populations of the small arthropods and crustaceans they favor. In turn, they are prey for a variety of fish and birds. The silversides congregate in the shallows, generally over sand or gravel bottoms with overhead cover if possible, but then move out to open water in search of additional food, which increases predation risk. They are often observed in a sort of daily migration pattern as a result.
The exact native range of the inland silverside is not known; they are widespread along the Atlantic coast from Maine
Maine
Maine is a state in the New England region of the northeastern United States, bordered by the Atlantic Ocean to the east and south, New Hampshire to the west, and the Canadian provinces of Quebec to the northwest and New Brunswick to the northeast. Maine is both the northernmost and easternmost...
to Florida
Florida
Florida is a state in the southeastern United States, located on the nation's Atlantic and Gulf coasts. It is bordered to the west by the Gulf of Mexico, to the north by Alabama and Georgia and to the east by the Atlantic Ocean. With a population of 18,801,310 as measured by the 2010 census, it...
, and along the Gulf of Mexico
Gulf of Mexico
The Gulf of Mexico is a partially landlocked ocean basin largely surrounded by the North American continent and the island of Cuba. It is bounded on the northeast, north and northwest by the Gulf Coast of the United States, on the southwest and south by Mexico, and on the southeast by Cuba. In...
. In the Mississippi River
Mississippi River
The Mississippi River is the largest river system in North America. Flowing entirely in the United States, this river rises in western Minnesota and meanders slowly southwards for to the Mississippi River Delta at the Gulf of Mexico. With its many tributaries, the Mississippi's watershed drains...
they can be found in backwaters and reservoirs as far north as Missouri
Missouri
Missouri is a US state located in the Midwestern United States, bordered by Iowa, Illinois, Kentucky, Tennessee, Arkansas, Oklahoma, Kansas and Nebraska. With a 2010 population of 5,988,927, Missouri is the 18th most populous state in the nation and the fifth most populous in the Midwest. It...
and Illinois
Illinois
Illinois is the fifth-most populous state of the United States of America, and is often noted for being a microcosm of the entire country. With Chicago in the northeast, small industrial cities and great agricultural productivity in central and northern Illinois, and natural resources like coal,...
, hundreds of miles inland.
They were introduced into Clear Lake and the Blue Lakes of California in 1967, in order to control the Clear Lake gnat Chaoborus asticopus and midge
Midge (insect)
Midges comprise many kinds of very small two-winged flies found world-wide. The term does not encapsulate a well-defined taxonomic group, but includes animals in several families of Nematoceran Diptera. While some midges are vectors for disease, many others play useful roles as prey items for...
s, and in lakes and reservoirs of Alameda County and Santa Clara County the following year. From there they spread into the San Francisco Bay
San Francisco Bay
San Francisco Bay is a shallow, productive estuary through which water draining from approximately forty percent of California, flowing in the Sacramento and San Joaquin rivers from the Sierra Nevada mountains, enters the Pacific Ocean...
and Central Valley, and have since become widespread in central California. In some areas, they are the most abundant fish of any species. Moyle suggests that this fish may have contributed to the demise of the Clear Lake splittail
Clear Lake splittail
The Clear Lake splittail was endemic to California's Clear Lake and its tributaries until its numbers severely declined due to competition from the introduced bluegill and alterations to the flow of inlet streams...
, although the effect of the silversides' introduction on California ecosystems not been much studied.
Inland Silversides are currently an EPA approved indicator species for acute marine aquatic toxicity testing and short-term chronic toxicity estimating of marine and estuarine organisms.