Atherinidae

Fishes of Canada's National Capital Region

Species Accounts

Atherinopsidae - New World Silversides - Poissons d' argent

Silversides are found mostly in temperate to tropical seas with some species in freshwaters. There are about 165 species with 3 in Canada and 1 in the NCR.

These small, elongate, silvery fishes have a short, spiny first dorsal fin widely separated from the second dorsal fin. The second dorsal often has a spine in front of the soft rays. Pelvic fins are usually abdominal and have 1 spine and 5 soft rays. Pectoral fins are high on the flank. The anal fin has 1-3 spines preceding the soft rays. Cycloid scales are usually large, extend onto the head and there is no lateral line although there may be a row of pits, 1 to each scale. Many species have a broad, silvery, iridescent lateral stripe which turns black in preserved fish. The oblique, terminal mouth is small as are the teeth. The swimbladder is not connected to the gut.

These fishes are found in large schools but are not commercially important in a direct sense. However they are major bait and forage fish for commercial species. They are usually found in shallow, inshore waters. Eggs of many species have filamentous outgrowths for attachment to seaweed, sand or rocks. Food is principally plankton. Some species from tropical waters are sold as aquarium fishes.

Brook Silverside / Crayon d'argent
Labidesthes sicculus (Cope, 1865)

Taxonomy

Other common names include Skipjack, Topwater, Friar and Glassfish.

Key Characters

This is the only freshwater family member in Canada and is easily recognised by the short, spiny, centrally placed first dorsal fin and longer soft second dorsal fin, both over a long anal fin.

Description

First dorsal fin spines 3-6 (this fin is small and easily missed), second dorsal fin with 1 spine and 9-13 soft rays. Anal fin with 1 spine and 20-27 soft rays and pectoral rays 12-13. There are 74-99 scales in lateral series, only a few of them pored. There are 24-29 long gill rakers.

Colour

Overall translucent with some internal organs visible, particularly in small fish. Preserved fish are opaque. The back is pale green to olive or yellowish, the flank has an iridescent silvery stripe outlined by a black stripe above. The belly is white or silvery. Scales on the back are outlined with dark spots. Fins are translucent but breeding males have a black tip to the first dorsal fin. Faber (1984c) illustrates a larva.

Size

Attains 11.2 cm.

Distribution

Found from the westernmost Québec in the Ottawa River and in the Rideau River both in the NCR, and the upper St. Lawrence River across southern Ontario to Georgian Bay and Lake Huron west to Minnesota, south to Gulf of Mexico drainages and Florida.

Origin

This species entered the NCR from a Mississippian refugium via a postglacial dispersal route.

Habitat

This silverside is found in surface waters in large schools in lakes and large rivers, but not brooks. The schools are not maintained through the night. Young fish avoid any solid objects perhaps as a mechanism to keep them out of shallow water where potential predators are found. The young swim with their heads touching the surface film of the water. Larger fish enter shallows. They are particularly intolerant of turbidity, a condition enhanced by urban development and agricultural activities. Their preferred temperature is 24.5°C.

Age and Growth

Life span seldom reaches 2 years and most fish die after spawning a year after being born. Growth is extremely rapid, 0.4 mm per day, reaching adult size in only 3 months. A one-year life cycle leaves this species susceptible to local extinction should some catastrophic event occur. Such an event would include ice build-up in shallow water.

Food

Food is water fleas, midge larvae, other insects and plankton, and flying insects and spiders which land on the water. These items are taken with a snap and some flying insects are taken by a leap out of the water. Leaps may be up to 10 times body length. Silversides are food for many sport and other fishes.

Reproduction

Spawning occurs in spring and summer (May-August) at 17-23°C over vegetation or gravel. Spawning is protracted, lasting at least 41 days. Males may defend a territory against other males. Territories eventually break down. Females are pursued by 1 or more males and may leap from the water followed by the males to a height of 2-3 cm landing up to 10 cm away. When caught by a male, the 2 fish glide downward with their bellies in contact and eggs are thought to be extruded and fertilised. Orange eggs are up to 1.4 mm in diameter and have 1-3 greatly elongate, adhesive filaments to attach them to vegetation. Some are deposited on floats and anchor ropes. There are up to 785 mature eggs present in a female at any time. Silversides in Florida have internal fertilisation and sperm are transferred by a short, genital palp when ventral surfaces of a breeding pair are pressed together. Whether this occurs in northern populations is unknown. Larvae hatch at 4.0-5.0 mm.

Importance

This species has been used as bait by anglers although it is not a legal bait fish in Ontario (Goodchild, 1990b). This species was placed in the "Not at Risk" category in 1989 by the Committee on the Status of Endangered Wildlife in Canada.

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