This document provides an overview of homeostasis in fishes. It discusses four main topics: osmoregulation, endocrine regulation, thermal regulation, and the immune response. For osmoregulation, it describes the four main strategies fishes use to regulate their solute and water concentrations in different environments. It also discusses the roles of gills, kidneys, drinking, and ion exchange in maintaining homeostasis. For endocrine regulation, it outlines the major endocrine tissues like the pituitary gland, thyroid gland, and gonads, and the hormones they produce. It notes fishes use behavior to regulate temperature within their tolerance ranges. Finally, it introduces the non-specific and specific components of the immune system that help protect fishes

1. Homeostasis
Chapter 7
Zoology 1450

2. Topics




Osmoregulation
Endocrine regulation
Thermal regulation
Immune Response (briefly)

3. Part 1: Osmoregulatory
Systems in Fishes
Maintaining homeostasis with
respect to solute concentrations
and water content

4. Introduction

Maintaining steady-state equilibrium in the
internal environment of aquatic and marine
organisms is challenging.

Much is done involuntarily (hormones, enzymes,
osmoregulation, etc.) so little physical action is
required, however…

“Pick-up-and-move” still an option!
(Poor environment.)

5. Definitions



Homeostasis = maintaining steady state
equilibrium in the internal environment of an
organisms
Solute homeostasis = maintaining equilibrium
with respect to solute (ionic and neutral solutes)
concentrations (i.e. salts)
Water homeostasis = maintaining equilibrium
with respect to the amount of water retained in
the body fluids and tissues

6. Definitions, continued
Osmotic concentration - Total
concentration of all solutes in an aqueous
solution.
Units
osmolals = 1 mole of solute/liter of water
milliosmolals = 1/1000th of one osmolal


7. Osmoregulation in different environments

Challenge to homeostasis depends on


Solute concentration of body fluids and
tissues…
…concentration of environmental solutes
marine: ~34 ppt salinity = 1000 mosm/l
 freshwater: < 3 ppt salinity = 1 - 10 mosm/l


8. Osmoregulation in different environments

Each species has a range of environmental
osmotic conditions in which it can function:
 stenohaline - tolerate a narrow range of
salinities in external environment
 euryhaline - tolerate a wide range of salinities
in external environment
 short term changes: estuarine - 10 - 32 ppt,
intertidal - 25 - 40
 long term changes: diadromous fishes
(salmon)

9. Four osmoregulatory strategies in fishes
1. Isosmotic (nearly isoionic, osmoconformers)
2. Isosmotic with regulation of specific ions
3. Hyperosmotic (fresh H20 fish)
4. Hyposmotic (salt H2O fish)

10. Osmoregulation Strategies
Osmoconforming (no strategy) Hagfish internal salt
concentration = seawater. However, since they live IN the
ocean....no regulation required!

11. Osmoregulation Strategies
Elasmobranchs (sharks, skates, rays, chimeras)

Maintain internal salt concentration ~ 1/3 seawater,
make up the rest of internal salts by retaining high
concentrations of urea & trimethylamine oxide
(TMAO).

Bottom line…total internal osmotic concentration
equal to seawater!

How is urea retained?

Gill membrane has low permeability to urea so it is
retained within the fish. Because internal inorganic
and organic salt concentrations mimic that of their
environment, passive water influx or efflux is
minimized.

12. Osmotic regulation by marine teleosts...




ionic conc. approx 1/3 of seawater
drink copiously to gain water
Chloride cells eliminate Na+ and Clkidneys eliminate Mg++ and SO4=
advantages and disadvantages?

13. active tran.
Saltwater teleosts:
passive diff.
H2O
drink
Na+, Cl-
Na , Cl
Na+, Cl-
Mg++, SO4=
Mg++, SO4=
chloride cells
kidneys
+
-

14. active
passive
Chloride Cell fig 6.2:
sea water
PC
pavement
cell
Cl-
+
carrier
internal
PC
Na+
Na+
Cl-
Na+, Cl-
gut
accessory
cell
Na+
Cl-
Na+
Cl-
K
+
chloride cell
pump
Na+
Na+ K+ ATPase
mitochondria
tubular system

15. Osmotic regulation by FW teleosts





Ionic conc. Approx 1/3 of seawater
Don’t drink
Chloride cells fewer, work in reverse
Kidneys eliminate excess water; ion loss
Ammonia & bicarbonate ion exchange mechanisms
advantages and disadvantages?

16. Freshwater teleosts:
don’t
drink
active
passive
H2O
Na+, Cl-
Na+, Cl-
water
Ion exchange
pumps; beta chloride cells kidneys

17. Ion Exchange Mechanisms
freshwater
interior
active
Na+
ATP
pump
NH4+ or H+
active
pump
gill membrane
ClATP
HCO3-

18. Freezing Resistance:

What fishes might face freezing?
hagfishes?
isotonic
marine elasmobranchs?
isotonic
freshwater teleosts?
hypertonic
marine teleosts?
hypotonic

19. Solution for Antarctic fish

Macromolecular
{
compounds
peptides (protein)
glycopeptides
(carbohydrate/protein)
rich in alanine

molecules adsorb (attach) to ice crystal surface

interfere with ice crystal growth (disrupt matrix)

Why is this important???
ice ruptures cells; hinders osmoregulation


20. What about rapid ion flux?
Euryhaline
 Short-term fluctuations in osmotic state of
environment, e.g. in intertidal zone or in
estuaries where salinity can range from 10
to 34 ppt with the daily tidal cycle:

these fish have both kinds of chloride cells
when salinity is low, operate more like FW fishes
 when salinity is high, operate like marine fishes
 kidneys function only under low salinity conditions


21. Euryhaline


Diadromous fishes (spend part of life in salt
water, part in freshwater – catadromous
(migrate seaward) or anadromous (migrate
up river)
hormone-mediated changes associated
with metamorphosis - convert from FW
adaptations to SW or vice versa, depending
on direction of migration

22. What about stress??

Stressors (handling, sustained exercise such as
escape from predator pursuit) cause release of
adrenaline (epinephrine) - for mediating escape, etc.

Adrenaline causes diffusivity of gill epithelium to
increase, i.e. “leaky cell membranes” water & ions)

This accentuates the normal osmoregulatory
challenge for FW or marine fishes

23. How to reduce stress in stressed fishes?

Minimize the osmotic challenge by placing
fish in conditions that are isosmotic


add salt to freshwater, e.g. in transporting fish
or when exposing them to some other shortterm challenge
dilute saltwater for same situation with marine
species

24. Thermoregulation in Fishes

25. Temperature effects on fish




Temperature exhibits the greatest influence on
fish’s lives!
Affects metabolism
Affects digestion
Signals reproductive maturation and behavior

26. Fish are conformers (well, sort of...)

Body temperature is that of the environment
(poikilothermic ectothermy)

Each species has particular range of
temperatures that they can tolerate and that
are optimal

Big difference!

27. Behavioral Thermoregulation in Fishes

Although fish are ectotherms, they can
alter their body temperature by moving to
habitats with optimal temperature

28. Hot Fishes

Some fish can maintain body temperature greater than
ambient - tunas, billfishes, relatives (nearly endothermic)

Tuna use retia (similar to rete mirable) in muscles to
conserve heat & exchange O2.


Also, red muscle is medial rather than distal
Billfishes have warm brains - heat organ from muscles
around eye

29. Practical application

You’re management decisions and
actions must account for fish responses to
temperature gradients and limitations

30. Endocrine Systems of Fishes

31. Pituitary Gland - Master Gland



Linked with hypothalamus of brain
Produces hormones that affect other
endocrine tissues - indirect influence
Produces hormones that affect nonendocrine tissues directly

32. Pituitary Gland

Indirect influence

ACTH - adrenocorticotrophic
hormone


TH - thyrotrophic hormone


stimulates interrenal tissue production
of cortisol, stress response
stimulate thyroid production of thyroxin
(growth, metamorphosis-i.e. flounder)
GTH- gonadotrophic hormone

stimulates gonads to produce
androgens/estrogens

33. Pituitary Gland

Effects non-endocrine tissues directly



pigmentation - melanophore stimulating hormone (MSH)
 affects long-term control of color
osmoregulation - prolactin, vasotocin
 controls fresh/saltwater systems
growth – somatotrophic hormone
 stimulates > length, cell multiplication

34. Thyroid Gland




isolated follicles distributed in connective tissue
along ventral aorta
controls metabolic rate
affects metamorphosis, maturation
facilitates switch between fresh & salt water

35. Gonads




gamete and sex hormone production
controls gametes maturation
cause formation of secondary sex
characteristics: color, shape, behavior
in fish, several sex hormones also serve
as pheromones - e.g. goldfish males
respond to hormones released with
ovulation

36. Other endocrine tissues in fishes

chromaffin tissues-located near kidneys & heart
 produce adrenaline/noradrenaline – “fight or flight”
 increases blood flow through gills, ventilation rate

interrenal (inside kidney) tissues
 produce cortisol, cortisone - stress response
hormones (reduce inflamation)

37. Other endocrine tissues in fishes

pancreatic islets
 produce insulin - controls glucose, glycogen
metabolism (glucagon production)

corpuscles of Stannius
 produce stanniocalcin - controls Ca2+ uptake at gills

38. Immune System

39. Introduction

Obviously, the immune system is important in
homeostatic processes.

Immune systems of fish have two components:
non-specific and specific.

As we will see, both are involved in protecting
fish from visible as well as invisible disease
causing agents.

40. Non-specific immunity

Skin & Scales—specific solid layers of protection
from pathological and chemical stressors.

Mucus secretion—traps microorganisms;
preventing entry into body cavity or circulation

Macrophages (phagcytes) and cytotoxic cells—
part of the inflamatory response which destroy
pathogens within the body before they can do
harm.

41. Specific Immune Response

More of an active response
where an “invader” is detected
and destroyed.

Primary organs: kidney,
thymus, spleen, intestine.

Antigens—invading
compounds which provoke an
immune response.
Source: Cancer Research Institute (2002) www.cancerresearch.org/immhow.html

42. Specific immune response: What if something does get in??

White blood cells called B lymphocyte cells (B cells) and
T lymphocyte cells (T cells)—bind to foreign cells and
begin replication and attachement to antigens (sort of
markers for things to come...).

Occasionally, invader actually goes trough a
macrophage first...then B cell responds...

Once B cells replicate, antibodies are produced which
bind specifically to pathogens and tag them for
destruction (eating) by macrophages!

44. “Looks like meat’s
back on the menu
boys!!!”

45. Questions???