fish is any aquatic vertebrate animal that is typically ectothermic (or cold-blooded), covered with scales, and equipped with two sets of paired fins and several unpaired fins. Fish are abundant in the sea and in fresh water, with species being known from mountain streams (e.g., char and gudgeon) as well as in the deepest depths of the ocean (e.g., gulpers and anglerfish). Food prepared from fish is also called fish, and it is an important food source for humans. They are harvested either from wild fisheries (see fishing) or farmed in much the same way as cattle or chickens (see aquaculture). They are also exploited by recreational fishers and fishkeepers, and are exhibited in public aquaria. Fish have had a role in many cultures through the ages, ranging from deities and religious symbols to the subjects of books and popular movies. Gelatin (from French gÃ©latine) is a translucent, colourless, brittle, nearly tasteless solid substance, derived from the collagen inside animals' skin and bones. It is commonly used as a gelling agent in food, pharmaceuticals, photography, and cosmetic manufacturing. Substances containing gelatin or functioning in a similar way are called gelatinous. Gelatin is an irreversibly hydrolyzed form of collagen. Gelatin is classified as a foodstuff, with E number E441. It is in some "gummy" candies as well as other products such as marshmallows, Jell-O, and some low-fat yoghurt. Some dietary customs forbid the use of gelatin from animal sources, and medical issues may limit or prevent its consumption by certain people. Gelatin is a protein produced by partial hydrolysis of collagen extracted from the bones, connective tissues organs, and some intestines of animals such as domesticated cattle, pigs, and horses. The natural molecular bonds between individual collagen strands are broken down into a form that rearranges more easily. Gelatin melts when heated and solidifies when cooled again. Together with water, it forms a semi-solid colloid gel. Gelatin forms a solution of high viscosity in water, which sets to a gel on cooling, and its chemical composition is, in many respects, closely similar to that of its parent collagen.  Gelatin solutions show viscoelastic flow and streaming birefringence. If gelatin is put into contact with cold water, some of the material dissolves. The solubility of the gelatin is determined by the method of manufacture. Typically, gelatin can be dispersed in a relatively concentrated acid. Such dispersions are stable for 10â€“15 days with little or no chemical changes and are suitable for coating purposes or for extrusion into a precipitating bath. Gelatin is also soluble in most polar solvents. Gelatin gels exist over only a small temperature range, the upper limit being the melting point of the gel, which depends on gelatin grade and concentration and the lower limit, the ice point at which ice crystallizes. The mechanical properties are very sensitive to temperature variations, previous thermal history of the gel, and time. The viscosity of the gelatin/water mixture increases with concentration and when kept cool (Ëœ 4 Â°C).