Osteichthyes Reproduction System

Instructor: Ebony Potts

Ebony has taught middle and high school physical science, life science & biology. She's also been an assistant principal and has a doctorate in educational administration.

Have you ever wondered how the fish that you eat reproduce? Some of the most common fish in the oceans are from a class of fish called osteichthyes. In this lesson you will learn about how these fish reproduce.

Gone Fishing

Have you ever gone fishing and caught a fish? If you have, you were probably not alone in the ocean, lake, or river in which you went fishing. There were probably other individuals out on the water as well, hoping to catch a nice lunch or dinner. But have you ever heard anyone say that there are no more fish in a lake, river or ocean? Of course not, because even though people fish and remove organisms from the water, fish reproduce. As fish are removed, they are replaced by the reproductive process. How does this happen though?

Since there are so many different types of fish with different methods of reproduction, we will focus today on one type of fish: the biggest class of fish in the ocean, the Osteichthyes.

Osteichthyes, the Bony Fish

Before we discuss reproduction, lets learn a little about the Osteichthyes. There are over 25,000 species of Osteichthyes, or ''bony fish.'' As their name suggests, most of these fish have a bony skeleton that is harder than some other fish. Many other fish, like sharks, have skeletons made of cartilage, a more flexible substance. Another interesting fact about Osteichthyes is simply the sheer number of them in our waters. They are the largest group of vertebrates (organisms that have a backbone) in the world, and 96% of all the fish in the ocean are a part of this class!

Reproduction in the Osteichthyes

Most Osteichthyes become sexually mature one to five years after they are born. Sexual maturity means that they are capable of producing offspring. Through this process, most Osteichthyes develop into either males or females. There are some hermaphroditic Osteichthyes, meaning they have both male and female sex organs, but they do not make up the majority of this class. The reproductive organs of the fish are called gonads, and in most fish they are paired. The gonads of the fish are internal and are located near the middle of its body, next to its stomach. Females have two ovaries that produce eggs, and males have two testes that produce sperm. The sperm and the egg cells are the sex cells of the fish.

When and where a bony fish reproduces is a cyclical process for most Osteichthyes, meaning that it happens on a timed and recurring basis. Most bony fish reproduce at least once a year, and the process is called spawning. Spawning may be triggered by changes in the amount of sunlight received daily, temperatures, tides and many other environmental factors. The trigger to spawn varies with each specific species.

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