Ichthyology, is the study and knowledge of fish that has been collected and observed by man for more that 2000 years. There are many different subjects that comprise ichthyology, but I am only going to hint on a few.
First, I would like to start with the classification of fish. The definition of fish: Any large group of cold-blooded, finned aquatic vertebrates. Fish are generally scaled, and respire by passing water over gills. Modern fish are divided into three classes: 1)AGNATHA, primitive jawless fish. Lampreys and Hagfish. 2)CHONDRICHTHYES, the jawed fish with cartilaginous skeletons. Sharks, Rays, and Rat-fishes. 3) OSTEICHTHYES, fish with bony skeletons. Lungfish, Trout, Bass, Salmon,
Perch, Parrot Fish.
1)class AGNATHA: this class contains the most primitive fish that lack a jaw and bony skeleton. The Lamprey and the Hag-fish are the only living members of this class that used to be an extremely large class. These fish lack true bones, but are very flexible. The hag-fish can actually tie itself in a knot to release a poison to fight of predetors. These fish lack scales and are very smooth to the touch. They have an oral sucker located in the middle of the mouth cavity that takes the place of the jaws. These fish live in fresh water and salt water, and some may live in both at different stages in their lives.
2)class CHONDRICHTHYES: members of this class include sharks, skates, rays, and ratfish. These fish have a cartilaginous skeleton, but have ancestors that were bony. These fish were the first to exhibit paired fins, lack swim bladders, have spiral valve intestines, exhibit internal fertilization, and have five to seven gill slits. They have cartilaginous upper and loosely attached lower jaws with a very significant variety of teeth. Their skin is covered with teehtlike denticles which give their texture the quality of sandpaper.
3)class OSTEICHTHYES: with over 20,000 species worldwide, the bony fish make up the largest section of vertebrates. The bony fishes have great maneuverability and speed, highly specialized mouths equipped with protrusible jaws, and swim bladders to control buoyancy. These fish have evolved to be almost any shape or size imaginable. Many of them have complex, recently evovled physiologies, organs, and behaviors for dealing with their enviornment in a sophisticated way.
Fish have developed three types of reproduction, that depend all on the way they care for their eggs.
1) Ovopartity- In 90% of the bony fish, undeveloped eggs are laid, and are fertilized externally.
2) Ovoviviparity- Internal development- without direct maternal nourishment. Advanced at
birth. Larval birth
3) Viviparity- Internal development- direct nourishment from mother. Fully
advanced at birth.
There is a lot more to fish reproduction than this, but there are other pages for that.
