EXTERNAL IDENTIFICATION - CHARACTERISTICS
a. Overview. To be able to inspect waterfoods properly, the inspector must first
be able to identify them. Fish identification characteristics are published in numerous
books on fish identification, which are normally available at inspection points. Some of
the external features for identifying species of fish are listed below. In addition, see
Figure 1-1. External Identification Features of Fish
b. Color. Color is sometimes used in identification. However, color is not
completely reliable as most fish are capable of considerable color variation. In addition,
the color of many fish fade after death.
c. Pattern. Patterns of the pigmented areas also change, although not as much
as the color.
d. Scales. Scales are used for identification in two ways.
(1) Each species of fish has a specific number of scales across or along the
(2) In many species of fish, the rate of growth differs markedly between
winter and summer months. Both species and age can be determined by a microscopic
examination of the scales.
e. Lateral Line. In most fish, the lateral line is a canal sunk into the skin that
runs in a longitudinal line along each side of the body. It starts just posterior to the gill
covers and extends the length of the body to the caudal (tail) fin. This canal contains
many sensitive nerve endings. Through these nerve endings, the fish can detect such
things as temperature changes, motion increasing or decreasing, and external pressure.
The lateral line is normally darker than the balance of the body and opens to the exterior