Fish endocrinology Flashcards
The hypothalamus can be referred to as what?
master regulator of hormones
The hypothalamus tells the brain when to _____ __ and communicates that to the ________.
wake up
pituitary
What is directly connected to the hypothalamus?
Pituitary gland
The pituitary gland is separated into what?
Anterior and posterior portions.
Is ACTH anterior or posterior?
What tissue does it act on?
Anterior
Kidney
Is TSH anterior or posterior?
What tissue does it act on?
Anterior
Thyroid
Is GTH anterior or posterior?
What tissue does it act on?
Anterior
Gonads
Is GH anterior or posterior.
What tissue does it act on?
Anterior
Acts on chloride cells and multiple tissues
Is PRL anterior or posterior?
What tissue does it act on?
Anterior
Osmoregulation
Is SL anterior or posterior.
What tissue does it act on?
anterior
plays a role in fat metabolism (adipocytes)
The hypothalamus is greatly affected by what?
Temperature, light availability and season
Is MCH anterior or posterior?
What tissue does it act on?
Posterior
Pigment cells
Is AVT anterior or posterior? What tissue does it act on?
Posterior
kidneys
Is isotocin anterior or posterior?
What tissue does it act on?
Posterior
osmorgulation
What is ACTH.
What does it do.
Adreno corocotropic hormone
ACTH tells the kidney to release cortisol.
What is cortisol?
Major stress hormone.
Also important in osmoregulation for making chloride cells.
(Important in growth effects)
The hypothalamus, through the anterior pituitary gland and ACTH thus regulates the _______ response, _________ and helps regulate _______.
stress
osmoregulation
growth
What is TSH?
What does it do?
Thyroid stimulating hormone.
Stimulates the thyroid to release thyroid hormone (different hormone) which is important in development and metamorphosis in fish.
What is GTH?
What does it do?
Gonadotropin hormone.
Tells the gonads to release stuff.
Controls the making of eggs.
What is GH?
What does it do?
Growth hormone.
Big effect on chloride cells, remaking them when moving into freshwater.
Helps with fish growth.
What is SL?
What does it do?
Plays a large role in fat metabolism.
During good times - store fat
During bad times - catabolize.
What is fat used for?
Make eggs or fight animals.
Both male and female fish will have __________ hormone, the effect will be different based on ____.
gonadotropin
sex
What is MCH?
What does it do?
Melanin concentrating hormone.
Concentrates melanin in pigment cells so the fish gets a darker colour.
Besides its use in colour, melanin causes something else. What is it?
Increases food intake.
What is the dual role of MCH?
Colour and food intake
______ controls changing colour for spawning.
MCH
What is AVT?
What does it do?
arginine vasotocin.
Largely controls water intake - similar to vasopressin.
Directly acts on kidney tubules and bladder.
When would AVT be secreted?
As migrating in habitats, teleosts want to change water balance in the kidneys.
What is isotocin?
What does it do?
In fish, isotocin is mostly used for osmoregulation, it affects salt balance in teleosts and osmobranchs.
In humans, what does isotocin do?
Same hormone co-opted for different function. Receptors are found in mammalian breast tissue and in uterine contraction tissue.
What is thyroid hormone implicated in?
1 - Promotes growth but has to work in conjunction with GH and IGF-1
2 - Metamorphosis in flatfish
3 - Salmon migration and metamorphosis
What is the role that TH plays in the metamorphosis of flatfish?
Eye migration and change in body shape.
What occurs if TH is blocked in flatfish and tadpoles?
Get large baby flatfish
Get really big tadpoles
What happens if TH is blocked in general?
May not grow as fast but will block development.
What does TH do for salmon migration?
Plays a role in upregulating the salt chloride cells and stimulating the production of a pigment giving the salmon a silvery colour.
May also be involved in homing/imprinting.
- may help olfactory system lock in the smell of natal stream
Where is the pineal gland located?
Under the skull
The pineal gland releases ________.
melatonin
_________ play a role in extraretinal photoreception.
pinealocytes
The pineal gland is a small gland sitting at the base of the _____ which can sense ______.
skull
light
Pinealocytes are ______-sensitive cells.
light
If a fish loses its eyes, how can it tell if it is day or night?
Can sense light levels through photoreceptors in pineal gland
What is a major role of melatonin?
Circadian rhythm
What does melatonin do?
Melatonin made in pineal gland, feedsback to hypothalamus which allows it to know what time of day it is.
If a fish is in complete darkness, will it still make melatonin?
Yes, still roughly 24hr cycle but, exposure to light fine tunes the cycle.
What are endocrine disruptors?
Give some examples.
Hormone-mimicking chemicals that alter reproductive cycles.
PCBs, plasticizers, synthetic estrogens
The antidepressants that we take affect fish through their ________ system.
endocrine
What are PCBs?
Common waste product of industrial activity which can, once broken down, act like fish hormones.
What are plasticizers?
Chemical used in water bottles to make them flexible which can have an estrogenic effect when they break down.
What is vitellogenin?
Important hormone for egg development, shouldn’t be present in male fish
What does vitellogenin do to fish?
Skewed sex ratios
Seeing eggs in male fish
Inhibition of spermatogenesis in adult males.
Hormones can change _______ through its effect on the hypothalamus.
seasonally
What are the 3 environmental controls that affect reproductive controls and behaviour?
Light
Pheromones
Temperature
How is light an environmental control?
Life’s indicator of seasonality, can tell if summer or winter by how long light is, picked up by retina and pineal.
How can temperature function as an indicator of seasonality?
If in shallow water in a thermally changing environment.
What is a pheromone?
Natural smell that comes out of animals
These smells are picked up by the olfactory system and have direct effects on the hormone cycle.
If there is lots of light, temperature is just right and lots of pheromones, it must be?
Breeding season
When its breeding season, lots of pheromones, how is the hypothalamus affected?
(JUST DRAW THE DIAGRAM)
Hypothalamus releases GRN (gonadotropin releasing hormone) which activates the gonads: testies or ovaries.
Male gonadotropin will cause the testes to release testosterone and 11-keto-test (basically the same).
- 11 keto test can act as pheromone when released in fish pee or from the gills
Two things these two do:
1 - Stimulate sperm production in the testes
2 - Stimulate male secondary sexual characteristics production (tubercles or hooknose for example)
Female gonadotropin:
- causes release of 17b-estradiol from ovaries and acts on the liver to cause release of vitellogenin.
17b-estradiol is the main fish estrogen and causes secondary sex characters in female fish
vitellogenin feedbacks to ovary causing egg maturation and finalizes yolk production
