Life In Water Flashcards
(11 cards)
Why is water being hyperosmotic to fish clades a challenge?
The hyperosmotic environment that fish live in causes them to lose freshwater, increase their osmolality, and lose turgor of their cell membranes due to the concentration gradient. This is due to the osmotic stress put on their cells.
What adapations do hagfish (Agnathads) have to overcome the hyperosmolality of sea water?
They are osmoconformers and can only tolerate a narrow range of salinity (stenohaline)
- Inorganic salt blood plasma concentration is the same as seawater.
How do elasmobranchs over come the challenges of living in a hyperosmotic environment?
They maintain an inorganic salt blood plasma concentration 1/3 of that of seawater. But they accumulate large amounts of organic compounds (urea and trimethylamine oxide, and other compounds), so that their internal osmolality matches that of sea water.
How do teleosts deal with the challenge of living in a hyperosmotic environment?
They have an internal salt blood plasma concentration 1/3 that of the surrounding seawater. Because they are always needing to drink saltwater to to make up for the loss of saltwater, they must excrete chloride ions across their gills to maintain salt balance.
Why is the density of water (800x that of air) a challenge?
Sinking incurs a large energetic cost. Fish must adapt ways to overcome this by maintaining neutral buoyancy when staying at a particular depth.
How do hagfish deal with the density of water?
Hagfish remain benthic except for brief anguilloform movements.
How do sharks overcome the density of seawater?
They store large amounts of lipids and squalene in their livers to bring their total body mass towards neutral. Their heterocercal tail and the angle of attack of their snouts and pectoral fins provides them with lift.
How do bony fish deal with the density of water?
Bony fish (teleosts) have a gas filled swim bladder that allows them to hang motionless in the water column while feeding. Their paired fins have a centre of mass that is also higher than the centre of buoyancy, allowing them to maintain balance and stability in the water column.
How do fish deal with the lack of dissolved oxygen in seawater?
All three fish clades have counter-current gas exchange in their gill filaments, which have a large surface area to allow for efficient oxygen transfer.
Teleost fish have a flexible operculum that allows them to constantly pump water over their gills.
Sharks use buccal pumping or ram ventilation.
Hagfish have multiple gill openings and use musculature pumping through their nostrils and pharynx.
Why is the high thermal conductivity of water an issue for fish (ectotherms)?
It causes heat loss to the surrounding seawater and reduced performance of their fast swimming musculature.
What convergent evolution has occurred in mackerel sharks (mako, GW) and tuna (bluefin) that allows them to overcome the challenges of heat loss in seawater?
Development of counter current heat exchange (rete mirabile) in the swimming musculature (red muscles) that conserves heat generated by metabolism and maintains body heat up to 8-12’C higher than their ambient temperature.
