NANFA-- gizzard shad musings

Christopher Scharpf (
Tue, 17 Oct 2000 23:53:08 -0400

Gizzard shads get their name from a muscular, thick-walled stomach that's
similar to the gizzards of wildfowl. Although generic separation of gizzard
shads from shads may be artificial (a gizzard is found in two other shad
genera), gizzard shad intestines are unique among clupeids; like that of a cow
and various herbivorous minnows, it's coiled or looped back upon itself so that
it can better digest and assimilate large amounts of vegetable matter.

How gizzard shad digest their food is unique among North America's fishes. They
feed primarily near the bottom, grazing over logs, plants, and other submerged
objects, filtering out algae and other microscopic plants through their long
gill rakers. What's unique is that gizzard shad do not immediately swallow their
food. Instead, they store it in special sacs at the top of their gill arches
called epibranchial organs. Here the food softens into a round mass, or bolus.
When the epibranchial organ is full, the bolus is passed down the pharynx into
the fish's gizzard-like stomach. Some people believe that gizzard shad eat mud.
True, gizzard shad that live in turbid water incidentally ingest mud, but the
belief that mud is a staple of their diet is probably due to the fact that by
the time the bolus reaches the intestine, it has been partially digested into a
mud-like consistency. It has also been suggested that gizzard shad eat sand;
though it's never been proven, sand may assist in the grinding of food in the

Gizzard shad prefer slower moving waters, moving upstream into shallower waters
to spawn. They spawn any time of day, with large aggregations of adults rolling
and tumbling near the surface.

Ecologically, gizzard shad are very important. They serve as a short and
efficient link between microscopic plant life and larger predators. Occasional
massive die-offs of shad provide an important source of food for waterfowl,
wading birds, and avian predators such as bald eagles.

Chris Scharpf

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