FISH AND SHELLFISH AS FOOD 283 



few hours at ordinary temperatures. The abdominal walls also break down 

 quickly. In fresh fish they are firm and elastic, but as the fish grow stale they 

 lose their strength and become soft and pulpy. 



A common criterion applied by nearly every housewife in the purchase of fish 

 is the examination of the gills. The gills of most fish are red in color, with certain 

 specific tints. These tints disappear in about 24 to 36 hours, and the gills become 

 yellowish and then brown or gray and slimy by the third to fourth day if the fish 

 are not kept at a low temperature. This test is not infallible as frequent washing 

 aids in the retention of the color; moreover the gills of trawled fish are often paler 

 at the time of capture than those of line fish; and, also, there are degrees of pale- 

 ness even among perfectly fresh fish. 



The eyes of fresh fish have a bright, transparent appearance which gradually 

 becomes cloudy and often turns pink or gray with decomposition. The eyes of 

 fresh fish often protrude, but when the fish are stale, the eyes tend to sink. 



The slime on fresh fish is transparent, almost colorless, and usually not enough 

 is present to be conspicuous except by feeling. As spoilage progresses, the slime 

 increases, becomes turbid and finally thick and often of a yellow color. Presence 

 of such slime is good evidence that the fish is not fresh, but its absence is meaning- 

 less since it can easily be removed. 



The characteristics of fresh fish and bad fish are presented in Table 63 : 



Table 63. Characteristics of Fresh and Stale Fish. 

 Good Fish Bad Fish 



Skin and colors bright Skin dull, spotted, or slimy; colors pale or 



bleached 



Scales adhere strongly Scales loose 



Eyes clear and not sunken or wrinkled Eyes cloudy, wrinkled, sunken 



Gills red Gills yellowish, gray, brown 



Flesh firm and elastic; finger impressions Flesh flabby and soft; finger impressions 



do not remain remain 



Smell fresh, at exterior and gills Smell stale or sour, especially at gills 



Little slime on skin (usually slime present Skin slimy (usually). In some species the 



but clear on halibut) slime is coagulated or lumpy; in halibut 



the slime leaves the fish 



Body rigid or stiff Body flabby or limp 



Fish sinks in water (usually), although Fish floats in water (if very bad) 



some will float if gassy 



Chemical Characteristics of Fresh Fish 



As previously indicated one of the first changes occurring after the death of a 

 fish is the onset of rigor mortis. Chemically an increase in the amount of lactic 

 acid and a very slight increase in hydrogen-ion concentration are noted. While 

 the fish is still in rigor mortis, or immediately after it passes off, the proteolytic 

 enzymes begin to hydrolyze the highly complex protein of the fish muscle into 

 simpler proteins, polypeptides, and amino acids. 



A second process, usually accompanying autolysis, is bacterial decomposition. 

 The result of bacterial actions on proteins is the formation of the same type of 



