Changes

* Primary ovarian cells line hollow cavities with folded walls.

* Primary ovarian cells line hollow cavities with folded walls.

** Oogonia are shed into this cavity, gaining a layer of epithelial cells in the process.

** Oogonia are shed into this cavity, gaining a layer of epithelial cells in the process.

** Become [[The_Ovary_-_Follicles_-_Anatomy_%26_Physiology|granulosa cells]], responsible for yolk formation in the developing egg.

** Become [[The_Ovary_-_Follicles_- Anatomy & Physiology|granulosa cells]], responsible for yolk formation in the developing egg.

* Ovarian [[The_Ovary_-_Follicles_-_Anatomy_%26_Physiology|follicle]] grows.

* Ovarian [[The_Ovary_-_Follicles_- Anatomy & Physiology|follicle]] grows.

** Hyaline zone forms between the oocyte and the epithelial cells - the zona pellucida.

** Hyaline zone forms between the oocyte and the epithelial cells - the zona pellucida.

* Primative

* Primative

* [[The_Ovary_-_Oocytes_-_Anatomy_%26_Physiology|Oocytes]] are released directly into the coelomic cavity

* [[The_Ovary_-_Oocytes_- Anatomy & Physiology|Oocytes]] are released directly into the coelomic cavity

* Enter the ostium

* Enter the ostium

* Travel through the [[Female_Reproductive_Tract_-The_Oviduct_-_Anatomy_%26_Physiology|oviduct]] and are eliminated.

* Travel through the [[Female_Reproductive_Tract_-The_Oviduct_- Anatomy & Physiology|oviduct]] and are eliminated.

==== Secondary Gymnovarian ====

==== Secondary Gymnovarian ====

* Salmonids and a few other teleosts.

* Salmonids and a few other teleosts.

* [[Female_Reproductive_Tract_-The_Ovary_-_Anatomy_%26_Physiology|Ovaries]] shed ova into the coelom

* [[Female_Reproductive_Tract_-The_Ovary_- Anatomy & Physiology|Ovaries]] shed ova into the coelom

* Go directly into the [[Female_Reproductive_Tract_-The_Oviduct_-_Anatomy_%26_Physiology|oviduct]].

* Go directly into the [[Female_Reproductive_Tract_-The_Oviduct_- Anatomy & Physiology|oviduct]].

==== Cystovarian ====

==== Cystovarian ====

* Most teleosts

* Most teleosts

* [[The_Ovary_-_Oocytes_-_Anatomy_%26_Physiology|Oocytes]] are conveyed to the exterior through the ovarian duct (not oviduct).

* [[The_Ovary_-_Oocytes_- Anatomy & Physiology|Oocytes]] are conveyed to the exterior through the ovarian duct (not oviduct).

** Ovarian lumen is continuous with the ovarian duct.

** Ovarian lumen is continuous with the ovarian duct.

==== Post-Oocyte release ====

==== Post-Oocyte release ====

* Postovulatory [[The_Ovary_-_Follicles_-_Anatomy_%26_Physiology|follicles]] are formed after [[The_Ovary_-_Oocytes_-_Anatomy_%26_Physiology|oocyte]] release

* Postovulatory [[The_Ovary_-_Follicles_- Anatomy & Physiology|follicles]] are formed after [[The_Ovary_-_Oocytes_- Anatomy & Physiology|oocyte]] release

** Do not have endocrine function

** Do not have endocrine function

** Wide irregular lumen

** Wide irregular lumen

** Rapidly reabosrbed in a process involving the apoptosis of [[The_Ovary_-_Follicles_-_Anatomy_%26_Physiology|follicular cells]].

** Rapidly reabosrbed in a process involving the apoptosis of [[The_Ovary_-_Follicles_- Anatomy & Physiology|follicular cells]].

* A degenerative process called follicular atresia reabsorbs vitellogenic [[The_Ovary_-_Oocytes_-_Anatomy_%26_Physiology|oocytes]] not spawned.

* A degenerative process called follicular atresia reabsorbs vitellogenic [[The_Ovary_-_Oocytes_- Anatomy & Physiology|oocytes]] not spawned.

**  This process can also occur, but less frequently, in [[The_Ovary_-_Oocytes_-_Anatomy_%26_Physiology|oocytes]] in other development stages.

**  This process can also occur, but less frequently, in [[The_Ovary_-_Oocytes_- Anatomy & Physiology|oocytes]] in other development stages.

=== Oviparity ===

=== Oviparity ===

* 97% of fish

* 97% of fish

* Mostly '''external fertilisation''', with the male and female fish shedding their gametes into the surrounding water.  

* Mostly '''external fertilisation''', with the male and female fish shedding their gametes into the surrounding water.  

* A few oviparous fishes practise [[Fertilisation%2C_Implantation_and_Early_Embryonic_Development_-Fertilisation-_Anatomy_%26_Physiology|'''internal fertilisation''']], with the male using an intromittent organ to deliver sperm into the genital opening of the female.

* A few oviparous fishes practise [[Fertilisation%2C_Implantation_and_Early_Embryonic_Development_-Fertilisation- Anatomy & Physiology|'''internal fertilisation''']], with the male using an intromittent organ to deliver sperm into the genital opening of the female.

** Species that pracitce [[Fertilisation%2C_Implantation_and_Early_Embryonic_Development_-Fertilisation-_Anatomy_%26_Physiology|internal fertilization]] include oviparous sharks, such as the horn shark, and oviparous rays, such as skates.

** Species that pracitce [[Fertilisation%2C_Implantation_and_Early_Embryonic_Development_-Fertilisation- Anatomy & Physiology|internal fertilization]] include oviparous sharks, such as the horn shark, and oviparous rays, such as skates.

**  In these cases, the male is equipped with a pair of modified pelvic fins known as claspers.

**  In these cases, the male is equipped with a pair of modified pelvic fins known as claspers.

* The newly-hatched young are called larvae.  

* The newly-hatched young are called larvae.  

== Reproductive Endocrinology ==

== Reproductive Endocrinology ==

In fish, as with all higher animals, [[Hormones_-_Anatomy_%26_Physiology|hormones]] play a critical role in the reproductive process. [[Hormones_-_Anatomy_%26_Physiology|Hormones]] are chemical messengers released into the blood by specific tissues, such as the [[Pituitary_Gland_-_Anatomy_%26_Physiology|pituitary gland]]. The [[Hormones_-_Anatomy_%26_Physiology|hormones]] travel through the bloodstream to other tissues, which respond in a variety of ways. One response is to release another [[Hormones_-_Anatomy_%26_Physiology|hormone]], which elicits a response in yet another tissue. The primary tissues involved in this hormonal cascade are the [[Hypothalamus_-_Anatomy_%26_Physiology|hypothalamus]],[[Pituitary_Gland_-_Anatomy_%26_Physiology|pituitary gland]], and gonads.

In fish, as with all higher animals, [[Hormones_- Anatomy & Physiology|hormones]] play a critical role in the reproductive process. [[Hormones_- Anatomy & Physiology|Hormones]] are chemical messengers released into the blood by specific tissues, such as the [[Pituitary_Gland_- Anatomy & Physiology|pituitary gland]]. The [[Hormones_- Anatomy & Physiology|hormones]] travel through the bloodstream to other tissues, which respond in a variety of ways. One response is to release another [[Hormones_- Anatomy & Physiology|hormone]], which elicits a response in yet another tissue. The primary tissues involved in this hormonal cascade are the [[Hypothalamus_- Anatomy & Physiology|hypothalamus]],[[Pituitary_Gland_- Anatomy & Physiology|pituitary gland]], and gonads.

* Reproduction occurs under environmental conditions that are favorable to the survival of the young.  

* Reproduction occurs under environmental conditions that are favorable to the survival of the young.  

* Long before spawning, seasonal cues begin the process of maturation.  

* Long before spawning, seasonal cues begin the process of maturation.  

** In many fish, this can take up to a year.

** In many fish, this can take up to a year.

* When the gametes have matured, an environmental stimulus may signal the arrival of optimal conditions, triggering [[The_Ovary_-_Ovulation_-_Anatomy_%26_Physiology|ovulation]] and spawning.

* When the gametes have matured, an environmental stimulus may signal the arrival of optimal conditions, triggering [[The_Ovary_-_Ovulation_- Anatomy & Physiology|ovulation]] and spawning.

** Examples of environmental stimuli are:

** Examples of environmental stimuli are:

*** Changes in photoperiod

*** Changes in photoperiod

*** Rainfall

*** Rainfall

*** Food availability.

*** Food availability.

* A variety of sensory receptors detect these cues, including the [[Eye - Anatomy & Physiology#Structure|eye]], [[Pineal_Gland_-_Anatomy_%26_Physiology|pineal gland]] (an organ in the dorsal part of the [[Forebrain_-_Anatomy_%26_Physiology|forebrain]] that is sensitive to light), [[Nose - Anatomy & Physiology|olfactory organs]], [[Tongue_-_Anatomy_&_Physiology#Taste_Buds|taste buds]], and thermoreceptors.

* A variety of sensory receptors detect these cues, including the [[Eye - Anatomy & Physiology#Structure|eye]], [[Pineal_Gland_- Anatomy & Physiology|pineal gland]] (an organ in the dorsal part of the [[Forebrain_- Anatomy & Physiology|forebrain]] that is sensitive to light), [[Nose - Anatomy & Physiology|olfactory organs]], [[Tongue_-_Anatomy_&_Physiology#Taste_Buds|taste buds]], and thermoreceptors.

* The [[Hypothalamus_-_Anatomy_%26_Physiology|hypothalamus]], located at the base of the brain, is sensitive to signals from sensory receptors and releases [[Hypothalamus_-_Anatomy_%26_Physiology#Outputs|gonadotropin releasing hormones (GnRH)]] in response to environmental cues.

* The [[Hypothalamus_- Anatomy & Physiology|hypothalamus]], located at the base of the brain, is sensitive to signals from sensory receptors and releases [[Hypothalamus_- Anatomy & Physiology#Outputs|gonadotropin releasing hormones (GnRH)]] in response to environmental cues.

* GnRH travels from the [[Hypothalamus_-_Anatomy_%26_Physiology|hypothalamus]] to the [[Pituitary_Gland_-_Anatomy_%26_Physiology|pituitary gland]].  

* GnRH travels from the [[Hypothalamus_- Anatomy & Physiology|hypothalamus]] to the [[Pituitary_Gland_- Anatomy & Physiology|pituitary gland]].  

* Gonadotroph cells of the [[Pituitary_Gland_-_Anatomy_%26_Physiology|pituitary]] receive [[Hypothalamus_-_Anatomy_%26_Physiology#Outputs|GnRH]] and release gonadotropic hormones into the bloodstream.

* Gonadotroph cells of the [[Pituitary_Gland_- Anatomy & Physiology|pituitary]] receive [[Hypothalamus_- Anatomy & Physiology#Outputs|GnRH]] and release gonadotropic hormones into the bloodstream.

** '''GTH-I''' has FSH-like activity.

** '''GTH-I''' has FSH-like activity.

** '''GTH-II''' has LH-like activity.

** '''GTH-II''' has LH-like activity.

* The gonadotropic hormones travel to the gonads, which synthesize steroids responsible for final maturation of the gametes.

* The gonadotropic hormones travel to the gonads, which synthesize steroids responsible for final maturation of the gametes.

** GTH-I binds to theca and granulosa cells of follicles.  This induces testosterone production by theca cells.  Testosterone then travels to the granulosa cells, where it is converted to oestrogen (as in mammals). Oestrogen induces vitellogenin (egg yolk precursor protein) production in the [[Liver_-_Anatomy_%26_Physiology|liver]].

** GTH-I binds to theca and granulosa cells of follicles.  This induces testosterone production by theca cells.  Testosterone then travels to the granulosa cells, where it is converted to oestrogen (as in mammals). Oestrogen induces vitellogenin (egg yolk precursor protein) production in the [[Liver_- Anatomy & Physiology|liver]].

** GTH-II binds to granulosa cells and induces production of progestins.   

** GTH-II binds to granulosa cells and induces production of progestins.   

* Maturation of the egg is a long process that involves complex physiological and biochemical changes. One important step, vitellogenesis, is a process in which yolk proteins are produced in the liver, transported to the ovary, and stored in the egg, resulting in tremendous egg enlargement. The yolk is important as a source of nutrition for the developing embryo.

* Maturation of the egg is a long process that involves complex physiological and biochemical changes. One important step, vitellogenesis, is a process in which yolk proteins are produced in the liver, transported to the ovary, and stored in the egg, resulting in tremendous egg enlargement. The yolk is important as a source of nutrition for the developing embryo.

** Finally, the walls of the germinal vesicle break down, releasing the chromosomes into the cell.

** Finally, the walls of the germinal vesicle break down, releasing the chromosomes into the cell.

* After the egg has matured, prostaglandins are synthesized.

* After the egg has matured, prostaglandins are synthesized.

**  Stimulate [[The_Ovary_-_Ovulation_-_Anatomy_%26_Physiology|ovulation]]

**  Stimulate [[The_Ovary_-_Ovulation_- Anatomy & Physiology|ovulation]]

* The egg is then released into the body cavity or ovarian lumen, where it may subsequently be released to the outside environment.

* The egg is then released into the body cavity or ovarian lumen, where it may subsequently be released to the outside environment.

* Following [[The_Ovary_-_Ovulation_-_Anatomy_%26_Physiology|ovulation]], the viability of the eggs can decrease rapidly.

* Following [[The_Ovary_-_Ovulation_- Anatomy & Physiology|ovulation]], the viability of the eggs can decrease rapidly.

== Sex Determination ==

== Sex Determination ==

* An asexual form of reproduction found in females where growth and development of embryos occurs without fertilization by males.  

* An asexual form of reproduction found in females where growth and development of embryos occurs without fertilization by males.  

* 100% female contribution.  

* 100% female contribution.  

* Self-activated [[The_Ovary_-_Oocytes_-_Anatomy_%26_Physiology|oocytes]] require no contribution from sperm.  

* Self-activated [[The_Ovary_-_Oocytes_- Anatomy & Physiology|oocytes]] require no contribution from sperm.  

* The offspring produced by parthenogenesis almost always are female in species where the XY chromosome system determines gender.

* The offspring produced by parthenogenesis almost always are female in species where the XY chromosome system determines gender.

* Occurs in very few fish species.

* Occurs in very few fish species.