Do fish only let water in though the mouth and out the gills? or can it be the other way around?
967973
It can be sucked in through the gills but it gets spit back out that way as a fish normally breathes.  The natural flow of water through the gills is due to swimming in that direction - the water naturally flow in the direction front to back.  Its not benefitting the fish to suck it in that way.
97410
Yes. \nFishes only have internal ear, that is to say, no opening to the body surface and no tympanic membrane, but the vibrations (sound waves) are transmited from the water to the inner ear through the body tissues. Sound travels really well inside the water, even if we (with our land-adapted hearing system) cannot hear much of it. \nIn addition, some groups of freshwater fishes have a special system that enhances sound hearing. This is called "Webberian apparatus" and consists of a chain of small ossicles (derived from the first trunk vertebrae) that are situated between the swimming bladder and the internal ear. Thus, when sound waves contact the swimming bladder (which acts like the membrane of a drum), it is amplified and transmitted to the inner ear by means of the vibration of these small bones. The fishes that possess this system (known collectively as "ostariophysean" (Ostariophysi) include well-known species such as catfish, tetras and characins, carps, and the electric eel. \n\nBirds, as all tetrapods, _do_ have a middle ear, but with only one ossicle (we mammals have three). They don't have external ears, but they have a short external auditory meatus (duct) so the tympanic membrane is not on the surface (as in frogs). Sound makes the tympanum vibrate, this vibration is transmitted through the ossicle (columella auris) and goes to the inner ear.
704415
Sounds like your fish has what is called ick. Here's is a site that you can get more information about it.
617384
Most fishes do have a 'tongue'. Fish tongues however do not resemble the muscular tongues of humans. The tongue of a fish is formed from a fold in the floor of the mouth. The tongue of the lamprey can be protruded from the mouth. It has horny teeth and is used to rasp flesh from its prey. Most fishes however cannot protrude their tongues. \n\nThe tongue and inside walls of the mouth of the Cottonmouth Trevally, Uraspis secunda, are brilliant white. \n\nSeveral species of parasitic crustaceans (isopods of the genus Ceratothoa) are known as tongue biters. These parasites are sometimes seen on the floor of a fish's mouth 'replacing' the tongue. Current evidence suggests that the tongue is pierced at the base by the pereopods (walking legs) of the isopod, resulting in it eventually being physically detached, or atrophying and then dropping off. \n\nSome species of tongue biters feed on the host's blood and many others feed on fish mucous. Tongue biters do not eat scraps of the fish's food. Most evidence indicates that these isopods do not kill the host.
1142424
Everyone is right:  because they have gills.\n\nBut, nobody seems to understand why gills do not work out of water.  It is true that the air we breath has more oxygen than most water, so the problem is not a lack of O2.  Also, the person that said they get  overdosed with O2 is incorrect.  \n\nGills are very delicate structures that are supported by the water.  Remember:  water is more dense than air.  So, the delicate (almost feathery) structures of gills that grab oxygen from the water will colapse when removed from the supportive water.
148170
i don't think that any protozoan does because they are single celled organisms; gills require diffusion of oxygen across a membrane directly to the blood. protozoans don't have blood. because just about all protozoans are aquatic, they have some kind of system to get oxygen into their cells, but not gill-like.
698474
Gills are poor for terrestrial organisms because gills absorb dissolved oxygen in water by direct diffusion through the blood vessels in the gills.  In the air gills would not be able to diffuse oxygen through the blood vessels and much water would be lost through the gill blood vessels.  Pretty much this would cause dehydration in an organism quickly.
520263
Well, their respitory system like their circulatory system allowed fish to live in the water for their entier lives. Most animals would die under the extreme water pressure and lack of breathable oxygen, but fish were able to adapt to live in the water.
114605
Having gills is prerequisite for being a FISH, dear. In fact, their scales secrete a gunk that acts as a laxative. Yes, they have a swim bladder, but it works more like a shark's liver than a typical swim bladder.
2105
The circulation of blood in fish is simple. The heart only has two chambers, in contrast to our heart, which has four. This is because the fish heart only pumps blood in one direction. The blood enters the heart through a vein and exits through an artery on its way to the gills. In the gills, the blood picks up oxygen from the surrounding water and leaves the gills in arteries, which go to the body. The oxygen is used in the body and goes back to the heart. This is a very simple closed-circle circulatory system.
537108
Mudskipper is not an amphibian because it does not have lungs.It breathes by gills and hence it is a fish.\n\nWhen other fishes are taken out of water their gill filaments stick and are unable to absorb gaseous oxygen and hence they die.But the mudskipper uses a technique in which it can retain water in enlarged gill chambers. They rotate their eyes to swill the water in the gill chambers around and keep the gills fluffed up and oxygenated. \nMudskippers also have to regularly replenish the water in their gill chambers so they cannot stay far from water. \nPlz check the site it might be of help to you.
461727
Fish have 2 major chambers (one auricle and one ventricle, plus one sinus venosus - before the auricle - and a conus arteriosus - after the ventricle). However, in the lungfishes there is a partial separation of both the main chambers, linked to the existence of a pulmonary blood circuit. \nAmphibians have two auricles and one ventricle, and the latter has deep "pockets" where oxygenated and deoxygenated blood goes, so that these two blood volumes do not mix much  while each flows through its respective circuit.\nReptiles... well, there is no such thing as a "reptile" really but rather three different groups. Both the turtles and the squamates (lizards and snakes) have two auricles and one ventricle, and the latter is partially separated by a spiral septum so that the pulmonary and body circuit do not usually mix (except in special circumstances). \nCrocodiles are related to birds, and just like them, they have a four chambered heart, with two auricles and two ventricles. However, in crocs the oxygenated and deoxygenated blood can get mixed because they have a hole between the paired main blood vessels that leave the heart. \nBoth birds and mammals have also four-chambered hearts with completely separate pulmonary and body circuits. \nCheck the link, there are good schematic illustrations and explanations for each taxon.
407668
They have mouth openings often with flagellum to help with their filter feeding.  The tail end is thinner and is lighter in color/more transparent.  Just do an image search for amphioxus and see!
1032129
Yes, about 40 times their body weight per day for fresh water fish. Water is constantly absorbed through the gills (by Osmosis) and has to be removed by the kidneys and then disposed of by urination
516056
Gall bladder of fish has nothing to do with the depth maintenance.\n\nIt is the AIR BLADDER in the abdomen of fish does the trick.
126853
I think fishes get thirsty if there is not enough oxygen in the water.
1006902
I think you mean gills.\n\nThere are artificial liquids available:\nLiquid breathing is a form of respiration in which a normally air-breathing organism breathes an oxygen rich liquid (usually from the perfluorocarbon family), rather than breathing air. It is used for medical treatment and could someday find use in deep diving and space travel. Liquid breathing is sometimes called "fluid breathing", but this is misleading as both liquids and gases are fluids.\n\nNanotechnology is be used to create respirocytes which act as artificial red blood cells and could allow you to hold your breath for 1-2 hours underwater.