# Do fish have barometers? **URL:** \ **Category:** Factual Questions\ **Created:** [March 19, 2001, 8:52pm UTC](https://boards.straightdope.com/t/do-fish-have-barometers/58620 "2001-03-19T20:52:44Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![Homebrew](https://avatars.discourse-cdn.com/v4/letter/h/c89c15/32.png) [@Homebrew](https://boards.straightdope.com/u/Homebrew)\ **Post date:** [March 19, 2001, 8:52pm UTC](https://boards.straightdope.com/t/do-fish-have-barometers/58620/1 "2001-03-19T20:52:44Z")
A co-worker who is an avid fisher is getting giddy as the weather warms and he can get out on the lake. During a fishing related conversation (almost all conversations with him involve fishing) he mentioned that fishing is least successful after a thunderstorm as the barometic pressure is rising. His reasoning was that the increased barometic pressure causes the little fish tummies to contract and makes them less hungry. I immediately called bullsh\*t. After a lengthy web search the only article I found was in [Bassmaster magazine](http://www.bassmaster.com/bassmaster_mag/1999_11_story.htm) from Nov. 1999 about weather and fishin’: > [@](#): > > When barometric pressure falls, as when a cold front is approaching, water pressure also decreases very slightly. This has no effect on fish directly; in fact, they can’t even feel the change in pressure. However, the change in water pressure can cause tiny plants and animals, the plankton, to become more buoyant and float upward, off the bottom and out of the weedbeds. This makes the plankton more available to minnows, which take advantage and start feeding. When the minnows are feeding, predator fish also become active and feed on the minnows. > > ÊÊÊ This is the time when sport fishing is best, and it’s predictable if you pay attention to the barometer. When the pressure is falling, you should get on the water and take advantage of the opportunity. But when the pressure is steady or rising, as when a cold front has just passed, you should expect things to slow down. IMNA Hydrologist or any other branch of science-ist, but I must say, this doesn’t sound convincing to me. Does barometic pressure affect water pressure? And even if it does would it be enough to affect plankton? What is really going on? ---
**Author:** ![mmmiiikkkeee](https://avatars.discourse-cdn.com/v4/letter/m/edb3f5/32.png) [@mmmiiikkkeee](https://boards.straightdope.com/u/mmmiiikkkeee)\ **Post date:** [March 19, 2001, 11:21pm UTC](https://boards.straightdope.com/t/do-fish-have-barometers/58620/2 "2001-03-19T23:21:07Z")
Some fish can indeed detect barometric changes such as when a low pressure system is moving in. The weather loach (originally from Britain I think) was used for these purposes, as they went all squirly and hyperactive when storms were approaching, hence the name. Low air pressures would affect water pressures (decrease them slightly), also causing the saturatation level of dissolved gases to change. In some rare cases in the Canadian praries (and probly elsewhere too), huge low pressure systems can temporarily give fish the bends as gases in their bodies come out of solution due to a relativly sudden drop in pressure; same as when you come up too fast from scuba diving. You’d think that fish would feel a difference inside them when the gas pressure in their swim bladders changes with shifting water pressures, although the overall change in pressure would be slight. I’m not sure about plankton rising from a drop in water pressure; plankton don’t contain much if any air (they float more by holding small lipid droplets inside them, water currents, and their body structure), but I’m not sure on that topic. It’s probly MORE a factor of decreased light levels due to clouds that come in with low pressure systems, which makes fish less spooky and more likely to feed. The wind and waves would churn the water more or perhaps from a different direction which would churn up plankton and other fish food = dinner time. AFTER the storm passes, the sun comes out (as do big fish predators), small minnows hide more, and the big fish are now full; so they just sit back and stop feeding/biting for a while - it has nothing to do with shrinking tummies. ---
**Author:** ![stuyguy](https://avatars.discourse-cdn.com/v4/letter/s/ec9cab/32.png) [@stuyguy](https://boards.straightdope.com/u/stuyguy)\ **Post date:** [March 20, 2001, 5:16am UTC](https://boards.straightdope.com/t/do-fish-have-barometers/58620/3 "2001-03-20T05:16:07Z")
Gee, **Homey,** didn’t you ever read those home science experiment books when you were a kid? If you did, this should sound familiar: Get: Large graduated cylinder (basically a tall cydinrical glass vessel), medicine dropper, small square of balloon-type sheet rubber, rubber band, water. Do: Fill cylinder with water; add the medicine dropper and squeeze out just enough air so that it is almost – but not quite – bouyant; cover the cylinder with the sheet of rubber and secure it with the rubber band. Now grab the middle of the rubber sheet and pull it upward. You will lower the air pressure above the water thusly expanding the air cavity in the dropper; this will, in turn, decrease its density. That will make it slowly rise to the top of the water. ---
**Author:** ![Duck\_Duck\_Goose](https://avatars.discourse-cdn.com/v4/letter/d/50afbb/32.png) [@Duck\_Duck\_Goose](https://boards.straightdope.com/u/Duck_Duck_Goose)\ **Post date:** [March 21, 2001, 1:15am UTC](https://boards.straightdope.com/t/do-fish-have-barometers/58620/4 "2001-03-21T01:15:17Z")
Yes, barometric pressure affects the water in a lake or ocean. Fish can sense changes in barometric pressure in their swim bladders. [http://www.basschamps.com/proarticledetail.cfm?articleid=194](http://www.basschamps.com/proarticledetail.cfm?articleid=194) > [@](#): > > It is a well-known fact that even minor barometric pressure changes affect a fish’s swim bladder. This air-filled sac is to a fish what the inner ear is to humans. When the barometric pressure rises quickly, it exerts pressure upon the bladder, thus affecting the fishes equilibrium — making it hard for the bass to maintain perfect balance. Naturally, this affects their behavior and appetite. [http://www.uiowa.edu/~c002134/complex/outline\_complex.htm](http://www.uiowa.edu/~c002134/complex/outline_complex.htm) > [@](#): > > an example in Indiana lakes > top predator: bass > prey of bass: minnows > prey of minnows: zooplankton > prey of zooplankton: phytoplankton Some kinds of phytoplankton can move. [http://www.oceansonline.com/phytoplankton.htm](http://www.oceansonline.com/phytoplankton.htm) > [@](#): > > The other group of phytoplankton we must mention are the dinoflagellates. These bizarre armored denizens of the lighted depths must surely be among the most remarkable organisms on Earth. Equipped with a battery of talents, there is just about nothing that these organisms don’t seem to be able to do. Consider: they photosynthesize; they eat other organisms; they can assimilate dissolved organic substances; they migrate up and down the water column; they have biorhythms; they bioluminesce; they produce toxic substances that prevent them from being eaten. These many characteristics must surely make them one of the more successful organisms. If they had any drawback, it would be that they are slow-growing. > > Dinoflagellates have cell walls that come in two varieties: naked or armored. Naked dinoflagellates, such as the bioluminescent Noctiluca, have smooth and flexible cells walls. Other dinoflagellates, such as the red-tide-causing Gonyaulax, has a cell wall that is composed of cellulose plates, given it an armored or helmeted appearance. Naked or armored, most dinoflagellates have two flagella, whiplike structures that provide locomotion, that rest within grooves, one groove rounding the periphery of the cell and the other groove running the perpendicular along the length of the cell. This arrangement of the flagella allows them to spin and move forward (or backwards, who can tell?). Many kinds of zooplankton can move. [http://www.soton.ac.uk/~pubaffrs/oczone/spr2000/story7.htm](http://www.soton.ac.uk/~pubaffrs/oczone/spr2000/story7.htm) > [@](#): > > Many zooplankton can move themselves significant distances both horizontally and vertically. It has been shown that some zooplankton make daily migratory journeys from deeper water where they live in daylight hours, up to shallower depths at night. These vertical migrations can be hundreds of metres each way – a big distance for animals only a few millimetres long. Conclusion: I don’t see why these living creatures who are capable of independent movement _shouldn’t_ be sensitive to changes in barometric pressure, the same way fish are. ---
**Author:** ![mmmiiikkkeee](https://avatars.discourse-cdn.com/v4/letter/m/edb3f5/32.png) [@mmmiiikkkeee](https://boards.straightdope.com/u/mmmiiikkkeee)\ **Post date:** [March 21, 2001, 3:26am UTC](https://boards.straightdope.com/t/do-fish-have-barometers/58620/5 "2001-03-21T03:26:29Z")
Those darn plankton huh? I imagine they too can detect barometric changes in some way, although the driving force of most planktonic migrations is light; there are usually daily migrations up and down to feed/photosynthesize. A lot of the moving plankton described are found in oceanic waters, and you don’t see migrations of several hundred meters up/down in a 50 foot deep bass pond. Remember that plankton are classed as plankton because overall they are at the mercy of the water currents as far as distribution goes; yes they can move about to find a comfy spot in relativly calm water, but they can’t swim against any appreciable currents or waves (no upstream migrations for these little guys). The currents sweep plankton to where ever they will, and fish generally follow.