Not necessarily - the Axolotl and newts both have gills - but they are not fish.
The major groups of fishes are that they can reproduce twice a day without any undeveloped process and the ink that Is incite of it's gills are common to there species
The term fishes refers to more than one species of fish, as in "There are many species of fishes." That said you could have any of the combination. School of fish - a group of fish made up of a single species, School of fishes - a group of fishes made up of more than one species. Shoal of fish - group of fish of the same species moving in roughly the same direction. Shoal of fishes - group of fishes of different species moving roughly in the same direction.
In Japanese tea garden the pond is called koi the fishes there is called biological filters.
An amberjack is any of several species of large food and game yellowtail fishes of the genus Seriola.
Any of numerous cold-blooded aquatic vertebrates characteristically having fins, gills, and a streamlined body and including the bony fishes, such as catfishes and tunas, and the cartilaginous fishes, such as sharks and rays.
Female bears of any species are called "sows", as in swine. Males are called 'boars".The female of any bear species is called a "sow".
Any one of numerous species of fishes belonging to Salmo, Salvelinus, and allied genera of the family Salmonidae. They are highly esteemed as game fishes and for the quality of their flesh. All the species breed in fresh water, but after spawning many of them descend to the sea if they have an opportunity., Any one of several species of marine fishes more or less resembling a trout in appearance or habits, but not belonging to the same family, especially the California rock trouts, the common squeteague, and the southern, or spotted, squeteague; -- called also salt-water trout, sea trout, shad trout, and gray trout. See Squeteague, and Rock trout under Rock.
fishes fishes
Any one of numerous edible, marine, spiny-finned fishes of the genus Labrus, of which several species are found in the Mediterranean and on the Atlantic coast of Europe. Many of the species are bright-colored.
The only "Cleaner fish" that I know of is the Marine species called the "Cleaner Wrasse". These fish pick parasites off other fish and will even swim into larger fishes gills and mouths to clean them too. If you are thinking of Catfish as being cleaner fish, then you have got things very wrong. Catfish are bottom dwelling fish but they do not clean up dirt and rubbish. They need fresh food just like any other fish. To the best of my knowledge no species of fish do well in a dirty tank.
There are many species of mushrooms with dark gills (or dark spores that make the gills look dark). Thus, the edibility of a mushroom cannot be determined based on the color of its gills alone.
Of course it does. You are simply mixing colours. Any colour covering over another one even if it is a transparent cover is bound to have an effect upon the perception of the colour behind. BTW. Putting artificial colouring in the fishes water is bound to have a negative effect on the fishes gills and breathing and therefore will be detrimental to the fishes health. Depending on the colouring agent you could cause instant and painfull death to the fish.