Fish

 

Section Overview

Overview of Fish

 

Section Overview

 

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-

rot fish.

 

Class Agnatha

 

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.

 

Class Chondrichthyes

 

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.

 

Class Ostieicthyes

 

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

Ostieicthyes.

 

 

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