1. Reproduction of Fish

2. Objectives To examine the reproductive anatomy of fish.
To analyze the different modes of reproduction among fish.
3. To describe the importance of induced spawning in fish.

3. The Reproductive System
Is the group of organs used in the reproductive process
Focuses primarily on gametes and the organs through which they are transported, stored and matured
Gamete – reproductive cell, such as a sperm or egg, capable of fusing with a gamete of the other sex in order to obtain fertilization

4. Fish Reproduction Involves three basic steps:
maturation: gametes develop so fertilization may occur
ovulation: eggs are released from the ovary
spawning: uniting of egg and sperm, causing fertilization

5. Fertilization Occurs when the sperm reaches the egg
sperm discharged into the water are chemically attracted to the eggs
eggs attract only sperm from the same species
the farther away from the eggs the sperm is emitted, the fewer eggs are fertilized

6. Male Fish Reproductive tracts include the following: testes
efferent ducts
epididymis
seminiferous tubules

7. The Testes
Are two elongated, oval shaped structures found inside the body cavity of fish on either side of the kidneys
Produce milt, which is the sperm-containing secretion of male fish
Increase in size during sexual maturity

8. The Efferent Ducts Transport mature sperm away from the testicles
Connect the testes to the epididymis
Emit the sperm from the body

9. The Epididymis Stores mature sperm
Allows sperm to further mature and gain the following abilities:
become motile (swim forward)
fertilize an egg

10. Seminiferous Tubules Are located inside the testicles
Convert the germ cells into spermatozoa
Release sperm outside the body to fertilize eggs
Germ Cells – basic structures from which new organisms develop; gametes prior to being sperm or eggs

11. Female Fish Reproductive tracts include the following: ovary oviduct

12. The Ovaries
Are located in the body cavity and connect to the peritoneum
House the female gametes known as ova
Produce hormones which regulate secondary sexual characteristics
Increase in size during breeding season, accounting for nearly 1/3 – 1/4 of the fish’s total body weight
Peritoneum – membrane lining the abdominal cavity

13. The Oviduct Is an open, funnel shaped organ located near the ovary
Draws mature eggs from the ovary
Delivers eggs from the ovaries to the outside of the body

14. The Ova Are the specialized female sex cells also known as eggs
Creates protective layers and travel from the ovaries to the oviduct and outside the body in oviparous animals
Are fertilized outside the body by sperm

15. Oviparous Animals
Produce eggs which mature and hatch after being expelled from the body
May or may not require internal fertilization
Include almost all fish

16. The Pituitary Gland
Is a small, oval gland which lies at the base of the brain
Is found in both males and females
Influences hormones and gonad functions

17. Modes of Reproduction In fish include the following: heterosexual
hermaphroditic
parthenogenic

18. Heterosexual Fish Use sexual reproduction
Possess only one sex’s reproductive organs
Require a member of the opposite sex in order to fertilize eggs

19. Hermaphroditic Fish Possess both male and female reproductive organs
May be divided into the following two categories:
synchronous: both sets of organs are active at the same time
sequential: only one organ is active at any given time

20. Parthenogenic Fish Use asexual reproduction
Are females which do not need a male in order to fertilize the eggs
Offspring lack diversity and may form adverse mutations

21. Reproductive Cycles Are the times of year fish will reproduce
Differ between species of fish
Occur during periods which will promote the best chances of survival for the fingerlings
Are influenced by environmental factors such as photoperiod, temperature and seasonal rainfall
Photoperiod – the amount of time during the day which a plant is exposed to light

22. Induced Reproduction
Is the injecting of hormones into fish to promote reproduction
Occurs in fish which do not breed in captivity due to the differences in captive and natural environments
May be used to manipulate the timing of reproduction to suit production needs

23. Induced Reproduction Most frequently occurs in the following two ways:
replicating natural environment
injecting hormones

24. Replicating the Natural Environment
Inducing spawning involves imitating conditions under which fish would reproduce in nature
Includes the following:
changing the amount of light fish receive
providing necessary vegetation, enclosed spaces or other factors depending on species of fish
altering water temperature

25. Hormones Most commonly injected are: pituitary extracts
purified gonadotropin
LHRHa
dopamine blockers
steroids

26. Pituitary Extracts Increase hormone levels
Are removed from the pituitary gland of a fish in order to obtain hormones which are then injected into another fish
Offer an expensive method of obtaining hormones which do not provide a long shelf life

27. Purified Gonadotropin
Stimulates the testes and ovaries and induces ovulation
Includes the following:
luteinizing hormone: promotes the production of testosterone
follicle-stimulating hormone: promotes the production of sperm in males and estradiol in females
Estradiol – the steroid which influences reproductive and sexual functioning in females

28. Luteinizing Hormones – Releasing Hormone Analogs (LHRHa)
Regulate the rate at which luteinizing hormones are released
luteinizing hormones aid in the production of testosterone and induction of ovulation
Are more pure and are not metabolized as quickly by fish than normal LHRH
May be used alone or in synchronicity with dopamine blockers

29. Dopamine Blockers Slow the rate at which dopamine is released
Enhance the strength of LHRHa in order to stimulate the pituitary gland
Dopamine – a chemical found within the brain which acts to regulate movement and emotion; slows down the functions of LHRH

30. Steroids Directly stimulate the gametes
Include injecting pure testosterone and estradiol into the fish

31. Determining Maturity of Fish
Includes recognizing the following characteristics:
females: rounded and soft abdomen; swollen, reddened, protruding genital area; swollen and reddened anal area; secondary sex characteristics are present
males: release milt when abdomen is gently pressed; secondary sex characteristics emerge

32. Determining the Sex of a Fish
May be easy in some fish while extremely difficult in others
Includes the following characteristics:
males are often larger and more colorful
males often have longer fins
females often have a plumper abdomen

33. Caring for Eggs and Fingerlings
Include the following techniques:
remove parents if they are aggressive fish
do not rapidly change water temperature or pH
do not move eggs
isolate eggs and fingerlings if in a community tank

34. Reproduction of Fish
ASSESSMENT

35. Assessment Which of the following describes milt?
Reproductive cell, such as a sperm or egg
Membrane living in the abdominal cavity
Sperm containing secretion of male fish used for fertilizing
Uniting of egg and sperm
Which of the following is NOT one of the three methods of reproduction?
Heterosexual
Hermaphroditic
Parthenogenic
Asexual

36. Assessment What is a gamete? Reproductive cell, such as a sperm or egg
Membrane living in the abdominal cavity
Sperm containing secretion of male fish used for fertilizing
Uniting of egg and sperm
Which of the following is NOT a reason producers induce reproduction?
To manipulate breeding seasons
Because it discourages the need to use hormones
To obtain more product
Because fish may not reproduce under captive conditions

37. Assessment 5. Female fish are usually brighter in color than males.
True
False
6. The efferent ducts transport mature sperm away from the testicles.

38. Assessment
7. Estradiol is the steroid which influences reproductive and sexual functioning in female fish.
True
False
8. The farther away from the eggs the sperm is discharged, the more eggs will be fertilized.

39. Assessment 9. Which of the following causes fertilization? Maturation
Ovulation
Spawning
None of the above
10. Eggs are also known as which of the following?
Ova
Germ cells
Gametes
Both A and C

40. Resources Hermaphroditism www.reefscapes.net
Fish Biology and Husbandry
Reproductive System
au.encarta.msn.com

41. Resources
Characteristics of Sexual Maturation of Wild and Hatchery Reared Baltic Salmon
Induced Reproduction in Fish
Hormonal Control of Reproduction in Fish for Induced Spawning
govdocs.aquake.org

42. Acknowledgements Project Coordinator: Production Manager:
Meghan Blanek
Production Manager:
Dusty Moore
Production Coordinator:
Brandon O’Quinn
Executive Producers:
Gordon Davis, Ph.D.,
Jeff Lansdell
Graphic Designer:
Ann Adams
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