Cycloid scales cover these teleost fish (rohu). The skin of most fishes are covered with scales. Scales vary enormously in size, shape, structure, and extent, ranging from strong and rigid armour plates in fishes such as shrimpfishes and boxfishes, to microscopic or absent in fishes such as eels and anglerfishes.The morphology of a scale can be used to identify the species of fish it came from.Cartilaginous fishes (sharks and rays) are covered with placoid scales. Most bony fishes are covered with the cycloid scales of salmon and carp, or the ctenoid scales of perch, or the ganoid scales of sturgeons and gars.Some species are covered instead by scutes, and others have no outer covering on the skin.ost bony fishes are covered with the cycloid scales of salmon and carp, or the ctenoid scales of perch, or the ganoid scales of sturgeons and gars. Some species are covered instead by scutes, and others have no outer covering on the skin.
definition : hydrometer. A hydrometer or areometer is an instrument that measures the specific gravity (relative density) of liquidsâthe ratio of the density of the liquid to the density of water. A hydrometer is usually made of glass, and consists of a cylindrical stem and a bulb weighted with mercury or lead shot to make it float upright.
1 The Alcometer is floated in the spirit to measure the alcohol content. 2  As alcohol is thinner than water, the higher in strength the alcohol is, the further down the hydrometer floats. 3  The reading is taken where the surface of the spirit cuts the scale of the hydrometer.