1 An even, light surface-the fish is bad if it has yellow spots and transparent parts on the surface. 2  Shiny and dry surface-bad fish has a coating of slime on the surface. 3  Fresh odour-sea-fresh, or neutral to weak odour.4  The fish is starting to go bad if it has a sharp, strong odour.he fish you buy in the shops isn't always as fresh as it should be. But it can be difficult to ascertain when the fish actually starts going bad. Today's methods of ensuring freshness aren't good enough because they only measure one indicator of whether the fish is fresh, such as texture, smell or colour.
The frequency of a wave is the number of waves produced by a source each second. It is also the number of waves that pass a certain point each second. The unit of frequency is the hertz (Hz). It is common for kilohertz (kHz), megahertz (MHz) and gigahertz (GHz) to be used when waves have very high frequencies.
The rate of its motion is 2 cycles/second. This rate is referred to as the wave frequency. Thus the wave frequency shows that how much the medium particles undergo in vibration when a wave is passed through that medium. It is cycles per second or waves per second or vibrations per second.he frequency is the quantity obtained when we divide velocity of the wave by its wavelength. f = $\frac{1}{T}$ where T = time period. The figure depicts the different types of waves as classified according to their frequencies.