## Friday, November 11, 2016

### Deep-Sea Fish Are Awesome!

During Professor Metzler’s 11/08/16 lecture on liquids, we talked about how the pressure an object experiences in liquid can be calculated by determining the magnitude of force perpendicular to an object and the object’s area. Ultimately, we talked about how the area of an object could be ignored when trying to determine the pressure an object experiences at a certain depth. I work in a comparative physiology lab at Colgate and I was recently tasked with switching the tanks for the sheepshead minnows—the tank had gotten dirty because the fish produce all sorts of waste from their diet of plant material, algae, and detritus. In order to switch their tanks:
1.     I took them out of their dirty tank and placed them in a small fish bowl. Then I cleaned their dirty tank.
2.     I placed a few rocks at the bottom of the clean tank and put about 1 L of water in the 35 cm X 35 cm X 35 cm tank.
3.     I placed the fish bank in the clean tank
4.     I put about 10 L more into the tank

As I did this, I wondered how much the pressure changed for the fish. With only 1 L of water, I assumed that the fish were nearly at the top of the water and the pressure they experienced from the water was negligible. As soon as I added the water back to their tank, they swam to about half the tank’s height (17.5 cm=.175 m)
P0= 1.01 X 10^ -5 N/m2
PF= (density water)(gravity)(depth)
= (1000 kg/m3)(9.8 m/s2)(.175)+ 1.01 X 10^-5
=1715 Pa
ΔP= Pf-P0= 1715-(1.01x 10^-5)= 1714.99 Pa

This is consistent with what reports say about where sheepshead minnows tend to live: “They prefer quiet, shallow waters and have been found in saltwater bays and estuaries, as well as coastal inland areas such as creeks, canals and ditches” (tpwd.texas.gov).

However, I was still curious about how deep-sea fish survive extreme pressures. Only about 2% of known marine species live in the deep-ocean area, called the pelagic environment. Within the pelagic zone, there’s the bathypelagic (1000-4000 m deep) and the abyssopelagic zones (4000-6000 m deep).
Bathypelagic: 9.8 x 106 Pa-3.92 x 107 Pa
(1000 kg/m3)(9.8 m/s2)(1000)=9800000= 9.8 x 106 Pa
(1000 kg/m3)(9.8 m/s2)(4000)= 39200000= 3.92 x 107 Pa

Abyssopelagic: 9.8 x 107 Pa- 5.9 X 107 Pa
(1000 kg/m3)(9.8 m/s2)(4000)=9800000= 3.92 x 107 Pa
(1000 kg/m3)(9.8 m/s2)(6000)= 58800000= 5.9 X 107 Pa

In the bathypelagic and abyssopelagic regions, no light enters this area of the ocean, so bioluminescence is common! This part of the ocean is also characterized by extremely low temperatures and low oxygen levels.

In comparison to the sheepshead minnows in the lab at Colgate, deep-sea organisms at 4000m (in between bathypelagic and abyssopelagic) experience over 20,000 times the pressure that a sheepshead minnow does.

Sheepshead minnow pressure: (1000 kg/m3)(9.8 m/s2)(.175)= 1715 Pa
Deep-sea organism (like the humpback anglerfish) pressure: 3.92 x 107 Pa
Ratio: 3.92 x 107 Pa/1715 Pa=22857

This led me to do some research on the biology that allows deep-sea fish to travel to such depths. How do these organisms not get crushed by the enormous pressure they experience?

Unlike humans, fish do not have compressible air pockets that would burst at really high pressures—thus the pressure balance can be maintained in between their bodies and the water. In addition to other adaptations, deep-sea fish have a compound called trimethylamine oxide, which basically ensures that proteins and other important molecules do not compress, denature, or completely alter their structure under extremely high pressures. These high pressures also mean that the cell membranes of fish are unsaturated—making them more loose and flexible. (A rigid cell membrane is usually bad for organisms). Some research also indicates that sulfur linkages between molecules in the cell membrane may play a key role. Evidently, studying these organisms is made more difficult by the fact that humans can’t actually travel that deep.
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