extreme example is Lemaeocera branchialis 

 found on cod and some other species (fig. 

 18). The copepod is located in the gill 

 chamber, but roots formed by extensions 

 of the body extend into the host, eventually 

 penetrating to the heart region. The life 

 cycle includes lumpfish, flatfish, and pos- 

 sibly others as intermediate hosts. 



Parasites of the Body Muscles 



Because the flesh of fish is the part that 

 is usually consumed by man, parasites and 

 diseases Eiffecting the body muscles of fish 

 are of primary concern. Though parasites 

 are killed by proper cooking, the presence 

 of worms or other abnormal conditions in the 

 flesh of food fish is esthetically and phy- 

 chologically disturbing, and many fish thus 

 affected are discarded unnecessarily. 



1. Protozoa are significant and sometimes 

 conspicuous parasites. Myxosporidia form 

 either spindle-shaped white nodules up to 



Figure 17.- -Parasitic copepods (Sphyrion lumpi) embedded in 

 redfish. Dissected copepod is shown at right. 



Figure \6.-- Lemaeocera branchialis from cod. Note the 

 ■■antlers"--anterior projections of the copepod tliat anchor it 

 in the flesh of the host. 



1 /Z inch in length or so-called "pus pockets" 

 in the flesh of small herring, alewives, 

 and menhaden from the east coast. 

 Myxosporidia are also responsible for the 

 conditions known as "jellied swordfish" on 

 the Atlantic coast and "wormy halibut" on 

 the Pacific coast. Both are characterized 

 by progressive destruction and liquefaction 

 of the muscles, producing unsightly areas 

 in the flesh that must be cut out and dis- 

 carded, or else the entire fish may be 

 discarded. 



Z. Fungus infections may produce muscle 

 abnormalities. A fungus infection of herring 

 on the east coast of North America produces 

 small yellow- white nodules. Advanced in- 

 fections result in extensive degeneration of 

 muscles, and diseased fish are difficult to 

 salt or smoke (fig. 19). Another symptom 

 of this fungus infection is the accumulation 

 of black pigment around spores in the flesh, 

 making the fish less desirable for filleting 

 and pickling. 



3. Larval trematodes occur commonly in the 

 flesh of many coastal marine fishes . Con- 

 spicuous in this respect are young Atlantic 

 herring, in which larvae of the fluke 

 Cryptocotyle frequently localize in the mus- 

 cles as well as underneath the skin, causing 

 black pigment accumulation and the forma- 

 tion of a conspicuous "pigment spot." Floun- 

 ders are frequently invaded by another 

 larval trematode which appears as a small 

 opaque white cyst in the flesh although there 

 is no pigment response. 



4. Larval nematodes in the flesh of marine 

 fishes best fulfill the popular conception of 

 "worms." They may occur free or encysted 

 in the muscles, and may become very active 

 when released. The so-called "codworm" 

 PoTocaecum has received particular attention, 

 especially on the Canadian east coast. This 

 larval roundworm encysts, sometimes in 

 great numbers, in the flesh of cod, smelt, 

 and other fishes (fig. ZO). Its life cycle is 

 not completely understood, but it involves 

 a succession of fish hosts, with the seal as 

 the final host for the adult worm. Other 

 kinds of larval roundworms may be found 

 in haddock and other commercial marine 

 fish, occasionally in great numbers, but 

 usually only a few in any single fish. 



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