FIsh Exam 2

What is position in the H2O column driven by?

-food availability

-O2 levels

-optimal temp for their physiology

-water pressure

-constraints on their foraging

Challenge of maintaining position in water column

Fish skeletons are denser than water

What challenges do bone density cause for fish

-translates to negative buoyancy (SINKING)

-can lead to constant energy expenditure to maintain position

Specific gravity for water/fishes

-Sea Water: 1.026

Cartilag. fishes: 1.1

Bony fish: 2

How do Chondricthyes handle buoyancy?

-no swimbladder/gasbladder

-rely on large, oil filled liver (SQUALENE-comes from food, liver produces)

What roles does Squalene serve?

-provides buoyancy

-can be used as an energy source

-helps with lipid processing

Liver for pelagic species are what percent of their body weight?

25-30%

Liver for Benthic species is what percent of their body weight?

5-10%

What does liver and body form provide?

Provides lift

Oil is ______ regardless of water pressure

Incompressable

-constant buoyancy regardless of depth

-can go up and down easily

How do Bony Fishes handle buoyancy

-mostly rely on swim/gasbladder

What type of bladder did ancestral Bony fishes have?

Physotomous bladder: open mouth cavity through a pneumatic duct

can release/take in air at waters surface

What type of swimbladder so modern body fishes have?

-Physoclistous bladder

No connection mouth closed

use glands/vascular areas + blood vessels to increase or inflation of bladder

Gas release for physostomes bladders

Can burp to release gas

can also use ovale-blood takes up additional across diffusion gradients→ dumps at gills→ expelled to environment

Gas release for Physocusts swim bladders

Rely on Ovale

Both bladder types rely on:

Gas Gland (heavily vascularized region of bladder)

In order for diffusion to occur

[gas]_blood > [gas]_bladder

Counter-current exchange

depends on Rete Mirabile

Acidification of blood leads to

Hemoglobin to dump oxygen → accumulation of O2 = CO2 at the gasbladder wall

Barotrauma

when fish are brought up too fast they cant equilibriate to lower pressure

Benthic fish bladder

NO bladder (or greatly reduced)

lost over evolutionary time

Pelagic species bladder

Often have no swim bladder because they often go up and down to catch prey

EX: tuna-bladder prescence is driven by habitat

Variable environments fish face

Water temp

Osmoregulation

Water temp heat sources

Ecotherms (EXTERNAL)

Endotherms (INTERNAL)

Body temp stability

-Homeothermy (constant)

-Poikilothermy (body temp varies with external conditions)

-Heterothermy (partial/regional endothermy.varies with body region)

Most fish are:

Ectothermic poikiotherms

As blood passes through gills, it quickly becomes some temp

Some fish can encounter wide range of temperature

Like the artic or tropics

Seasonal change in temperate zones can cause some extremes in temperature

Winter and summer

Challenge with body temps in winter

As water temp declines → fish body temp declines → metabolic rate declines

-Causes less energy for maintaining body systems and function

-And major changes to enzyme systems and membrane funtion

How do some fish compensate for extreme temp changes?

-Higher production/concentration of key metabolic enzymes (surplus for cold periods)

-Some fish have multiple temp dependent forms of key enzymes (switch to “cold water” form)

-maintain membrane fluidity (prevent solidification)

-Higher mitochondria production in red muscle tissue-aids in maintaining energy production and metabolic function

Winterkill

anoxia/low O2 during winter under ice

-shallow lakes with higher organic matter productivity + high bacterial activity

What challenges do antartic/artic fishes face?

“constant” cold water temp conditions

-ice crystal formation in/outside cells + cells dehydrate/collapse → cells rupture or damage

Why dont freshwater fishes have ice crystal formation in cells?

intercellular fluids below freezing point of freshwater (?)

Why dont sea fish have issues of ice crystals in cells?

Higher solute conc leads to lower freezing points

Strategies to handle ice crystals in Antartic/artic oceans

-produce antifreeze compounds/proteins (these cover ice crystals, blocking them from increasing in size)

-some fish have higher glycerol levels in blood → lower freezing point

-some fish use homeothermy (regional endo/heterothermy)

Challenge with using homeothermy

Requires way more energy

-lose heat to water as blood passes through gills → eat more to compensate → higher metab rate

Solution to challenges with homeothermy

Counter-cuurent exchange for heat associated with blood

-depends upon blood vessels close to each other (rete mirable) for heat transfer

Coldwater sharks that DONT rely on heterothermy

rely on higher solute in blood (urea) → lowers freezing point

-slow metabolism → longevity and growth rate

Which fish have regional heterothermy?

-Scombridae (tunas, mackerels)

-Laminidae sharks (great whites, makos)

-Billfish

Regional heterothermy

They all maintain high temp of certain tissues/regions/organs

Skeletal/swimming muscle (regarding regional heterothermy)

-Used by all

-heat from red muscle

-use countercurrent exchange to reduce heat loss across gills (incoming blood is warmed, body heat consumed)

Brain and eye (regional heterothermy)

-as water temp decreases, eye/brain function reduce

-Billfish and tuna: produces heat to maintain eye function and heats brain

Sharks: have retes near eyes-heat exchange

High water temp challenges

-As water temp rises, dissolved oxygen and oxygen solubility reduces

-Hemoglobin-affinity for O2 reduces with higher temp

-With higher water temp, enzymes denature/dont function- alters membrane function

Solutions for high water temp

Multiple hemoglobin forms. some have higher affinity for O2 under higher water temp than others

What fish are better equipped to handle low O2 envrionments?

Toadfish

Hemoglobin has higher affinity

Aerial breathing

typically modified swim bladder or true lungs

Gulping at surface (mouth)

(High water temp)

Osmoregulation with fish

-Managing water/ion balance within their tissue, cells, fluids relative to external environment

-If homeostatic system not maintained, can lead to fish death

How do fish regulate gain/loss of water and ions relative to external environment

-Na, Cl, Mg, K, SO4, Ca determine solute within organ tissue

Cell tonicity

Characterizes water/ion balance

Isotonic

solute same in/out

No water movement

Hypotonic

More solute in than out

Water moves INTO cell, OVER-hydration

Hypertonic

More solute out than in

Water moves OUT of cell, Dehydration

What kind of osmosis do freshwater fish have?

Hypertonic to environment

GAIN water

LOSE ions/salts/ solutes

How do freshwater fish manage osmosis challenges?

• Lower water gain → scales lower uptake across

-excretion of higher dilute urine- some loss of salts

• Salt retention → scales lower loss to environment

-kidney glomerulus - uses active transport to pull ions/salts out of plasma (returns to system)

-Chloride cells in gill-actively transport salts in against conc. gradient