Overview of Fish
The following discussion is from "A Quick Course in Ichthyology"
by Jason Buchheim, Director, Odyssey Expeditions. It has been
abridged and editted for the Nature Guide.
Of all the animals inluded in the Nature Guide, fish are the least con-
spicious component of the ecology of Sky Meadows State Park. Re-
stricted in distribution to two primary areas (Turner Pond and Gap
Run) and often not readily observed from trails, fish have not been
systemically studied. Future research into the various fish species
inhabiting the park needs to be conducted. In addition, the fish in
Sky Meadows State Park can be divided into two categories: 1) na-
tive fish occurring in Gap Run, and 2) "stocked" fish in Turner Pond.
While the first category is probably relatively stable in species com-
position, and latter category can vary over time.
Overview of Fish
Worldwide, there are over 22,000 species of fish, comprising more
than 50% of all vertebrate species. The origin of fishes dates back to
over 480 million years. Fish evolved in fresh water; the chondrichthyes
moved to the sea early in evolution, while the bony fishes went through
most of their evolution in fresh water and spread to the seas at a much
later period. Fish are the dominant free swimming animals of the seas.
The structure of a fish body is designed for ease of movement. This
ability to move about easily, without relying on water currents to carry
them about, has enabled fishes to exploit most parts of the world's oceans,
and this is reflected in an extraordinary variety of sizes and shapes. Fish
are found in both fresh and salt water worldwide, and are a very impor-
tant food source for many nations.
Fish can be defined as any of a large group of cold-blooded, finned aquat-
ic vertebrates. Fish are generally scaled and respire by passing water over
gills. Fish come in all shapes and sizes, some are free swimming, while
others rest on the bottom of the sea, some are herbivores and others are
carnivores, and some lay eggs while others give live birth and parental
care to their young.
Modern fish are divided into three classes: 1) Agnatha, primitive jawless
fish; incudes lampreys and hagfish, 2) Chondrichthyes, the jawed fish with cartilaginous skeletons; includes sharks, rays, rat-fishes, and 3) Osteichthyes,
fish with bony skeletons; includes lungfish, trout, bass, salmon, perch, par-
Fish of the Class Agnatha ("no jaw") are the most "primitive" of the fishes;
they lack a jaw and a bony skeleton. The hagfish and the lamprey are the
only living representatives of this once large class. As they lack true bones,
these fish are very flexible, the hagfish can actually tie itself in a knot to rid
itself of a noxious slime it can produce to deter predators. They have a
smooth, scale less skin and are soft to the touch. In place of the jaws is an
oral sucker in the center of which is the mouth cavity. Many of the agnathas
are highly predatory, attaching to other fish by their sucker like mouths,
and rasping through the skin into the viscera of their hosts. The juvenile
lamprey feeds by sucking up mud containing micro-organisms and organic
debris - as did the primitive agnatha. Agnathas are found in both fresh and
salt water and some are anadromous [living in both fresh and salt water at
different times in its life cycle]. The hagfish has no eyes, while the lamprey
has well-developed eyes.
Members of the Class Chondrichthyes ("cartilage-fish") include the sharks,
skates, rays, and ratfish. These fish have a cartilaginous skeleton, but their ancestors were bony animals. These were the first fish to exhibit paired fins. Chondrichthyes lack swim bladders, have spiral valve intestines, exhibit
internal fertilization, and posses 5-7 gill arches (most have 5). They have cartilaginous upper and loosely attached lower jaws with a significant array
of teeth. Their skin is covered with teethlike denticles which gives it the tex-
ture and abrasive quality of sandpaper.
Sharks are animals that are superbly adapted to their environment. Almost
all are carnivores or scavengers, although the species that live close to the
sea floor feed mostly on invertebrates. Most possess a keen sense of smell,
a large brain, good eyesight, and highly specialized mouth and teeth. Their
bodies are usually heavier than water, and they do not have an air filled
swim bladder for buoyancy like most bony fishes. All sharks have an asym-
metric tail fin, with the upper lobe being larger than the lower one. This
feature, together with flattened pectoral fins, and an oil-filled liver compen-
sates for the lack of a swim bladder. There are 344 known species of sharks
living in all parts of the oceans, from shallow to deep water and from the
tropics to the polar regions. A few even venture into fresh water and have
been found in rivers and lakes. Contrary to popular belief, most sharks are harmless to humans.
The bony fish comprise the largest section of the vertebrates, with over
20,000 species worldwide. They are called bony fish because their skele-
tons are calcified, making them much harder than the cartilage bones of
the chondrichthyes. The bony fishes have great maneuverability and speed,
highly specialized mouths equipped with protrusible jaws, and a swim
bladder to control buoyancy.
The bony fish have evolved to be of almost every imaginable shape and
size, and exploit most marine and freshwater habitats on earth. Many of
them have complex, recently evolved physiologies, organs, and behaviors
for dealing with their environment in a sophisticated manner.
All fish in Sky Meadows State Park are presumed to be members of Class
Crooked Run Valley