דגים - רבייה וחיזור בדגים

Summary

This script explores the diverse and fascinating reproductive behaviors of fish, highlighting external and internal fertilization, unique mating rituals, and parental care. It delves into the processes of semelparity and iteroparity, where some fish reproduce once while others do so multiple times. The script also discusses the extraordinary phenomenon of sex change in fish and sexual parasitism, where small males attach to females as reproductive organs. With vivid examples from species like sticklebacks, salmon, and seahorses, the video offers a captivating look into the complex world of fish reproduction.

Takeaways

• 😀 Fish reproduction in most teleosts is external, with females releasing eggs into the water and males fertilizing them externally.
• 😀 Some fish species exhibit semelparity, where they reproduce only once after reaching maturity and then die, such as in salmon and eels.
• 😀 Most teleosts practice iteroparity, meaning they can reproduce multiple times throughout their life.
• 😀 A few fish species have internal fertilization and give birth to live young, while some offer parental care to their offspring.
• 😀 Fish can change sex during their lifetime, with some species exhibiting sequential hermaphroditism (e.g., female turning into male or vice versa).
• 😀 Fish courtship behavior can be complex, as seen in the stickleback fish, where males perform a zigzag dance and display their red bellies to attract females.
• 😀 After fertilization, the fertilized eggs develop into larvae (e.g., the sac fry of salmon), which initially feed off the yolk sac.
• 😀 In some species, fish create nests to protect their eggs, either by digging holes in the ground or creating bubble nests (e.g., betta fish).
• 😀 Some fish species (e.g., seahorses) have a unique reproductive process, where the male carries the fertilized eggs in a brood pouch until they hatch.
• 😀 In certain species like the mouthbrooding cichlids, the female holds the fertilized eggs in her mouth until the larvae hatch and are protected inside until they are strong enough to swim away.
• 😀 Sexual parasitism is observed in some fish, where smaller males latch onto females and essentially become parasitic sperm producers while losing all other bodily functions.

Q & A

What is external fertilization, and how does it work in most fish species?

External fertilization is the process where female fish release their eggs into the water, and males release sperm to fertilize the eggs externally. This method is common in many species of fish, such as salmon and eels, where fertilization occurs in the aquatic environment.

What is the difference between semelparity and iteroparity in fish reproduction?

Semelparity refers to species that reproduce only once in their lifetime, such as salmon and eels, after which they die. Iteroparity refers to species that reproduce multiple times throughout their lives, as seen in most fish, which breed in successive seasons.

Are there fish species that provide parental care? If so, can you provide an example?

Yes, some fish species provide parental care. For example, male sticklebacks build and defend nests, protecting the eggs and young. Similarly, some species like seahorses have males that carry the developing embryos in a pouch until they are ready to be released.

How does the courtship behavior of the stickleback fish work?

The male stickleback displays a red belly during breeding season to attract females. He then performs a zigzag dance, turning sharply in 180-degree angles. If the female is attracted, she follows him to the nest where he encourages her to lay eggs, after which he fertilizes them.

What is the difference between internal and external fertilization in fish?

External fertilization occurs when the eggs are fertilized outside the female's body, typically in water, as seen in species like salmon. Internal fertilization happens when males transfer sperm directly into the female’s body, leading to fertilization within her, and is seen in species like guppies and mouthbrooding cichlids.

What is sequential hermaphroditism, and how does it work in fish?

Sequential hermaphroditism is when a fish changes its sex during its life. For example, in some species like wrasses, females can become males when there is a lack of males in the group. This change is not only external but also involves functional alterations in reproductive organs.

Can a female fish turn into a male? Give an example.

Yes, in some fish species, a female can turn into a male. One example is the wrasse, where females can change to males, especially in the absence of other males. This allows them to maintain the breeding structure of their group.

What is sexual parasitism in fish, and how does it work?

Sexual parasitism in fish occurs when smaller males attach to larger females and become parasitic. These males lose most of their organs except for their testes, and their only role is to release sperm to fertilize the female's eggs.

How does fertilization occur in fish species with external fertilization like salmon?

In species like salmon, external fertilization occurs when the female lays her eggs on the riverbed or in a nest. The male then releases sperm over the eggs to fertilize them. This process happens in open water, with the fertilization being completed after multiple releases of sperm.

How does the reproductive strategy of the seahorse differ from most fish?

In seahorses, the male plays a unique role by carrying the fertilized eggs in a specialized pouch on his abdomen. The female transfers the eggs to him, and he fertilizes them. The male then carries the embryos until they hatch and are released as fully developed young.