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.
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.
The majority of bony fish reproduce via external fertilization of their eggs. During spawning season for the fish, the females and the males release hundreds and sometimes thousands of eggs and sperm into the water. The eggs are fertilized in the water. Once the eggs are fertilized, some fish guard their eggs and others offer no care at all. Many of the fertilized eggs are eaten by other organisms.
However, many survive and live long enough to start the reproductive cycle again.
- Osteichthyes have a bony skeleton and are the largest group of vertebrates in the world.
- 96% of all the fish in the ocean are Osteichthyes.
- Most Osteichthyes become sexually mature one to five years after birth.
- The reproductive organs are called gonads.
- Females have two ovaries that make eggs, and males have two testes that make sperm.
The sperm and the egg cells are the sex cells of the fish.
- Spawning or reproduction is cyclical and usually happens at least once a year.
- Spawning can be triggered by the amount of sunlight received daily, temperatures, tides and many other things. The trigger to spawn varies with each specific species.
- Fertilization for most Osteichthyes occurs externally, females release eggs and males release sperm that are fertilized in the water.
- Many of the fertilized eggs will eaten, but some many survive to start the reproductive cycle again.