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.
Wavelength is usually measured in meters (m). Frequency is the number of cycles of a wave to pass some point in a second. The units of frequency are thus cycles per second, or Hertz (Hz).n fact, X-rays and gamma-rays are usually described in terms of energy, optical and infrared light in terms of wavelength, and radio in terms of frequency.