30 Am.ericcm Fisheries Society. 



found encysted in the liver and other internal organs in 

 large numbers and no doubt interfere with the functioningof 

 the organs containing them. Round worms, and especial- 

 ly the Acanthocephala, or thorn-headed worms, occur in the 

 intestine where they attack the lining membrane. Leeches, 

 crustacean parasites and some others may attack the skin 

 and subject the fish to infection by the deadly fish fungus 

 (Saprolegnia.) 



Parasites produce the deadliest effects in the young fish. 

 Certain protozoan parasites, unicellular, miscroscopic organ- 

 isms, attack the skin of the young bass, even before they have 

 left the nest. While these do not remain long to affect the 

 fish, usually being gone before the young reach an inch in 

 length, they may cause the death of many of the young fry 

 by forming pustules in the skin which break to the outside. 

 These were abundant on young small-mouthed bass about 

 Put-in-Bay in June and caused considerable loss. 



Internal parasites begin to affect the young bass as soon 

 as they begin to feed. The first of these to make their 

 appearance are young tape worms and fluke worms which 

 have their larval stages in the minute Crustacea (water 

 fleas) which form the first natural food of the bass and most 

 other fishes. The presence of large numbers of the early 

 stages of these parasites at a time when the bass fry were 

 still feeding entirely on these minute Crustacea, called the 

 attention of the writer to the fact that the parasites must 

 inhabit these Crustacea as their intermediate host. A for- 

 mer graduate student, Br. R. V. Bangham, took up the prob- 

 lem and traced various species of tapeworms and fluke 

 worms back to the species of Crustacea which carry them. 

 It is no uncommon thing for a young bass less than an inch 

 long to harbor a score or more of these parasites and oc- 

 casionally the number is much greater than this. They 

 sometimes grow to maturity in the intestine of the bass, or 

 they may penetrate the wall of the intestine and encyst 

 themselves in the liver, spleen or other internal organs. 

 Sometimes the liver is so full of these young parasites that it 

 appears to have been riddled by them and there seems no 

 doubt that they may cause the death of the fish. More fre- 

 quently, it is probable they merely delay the development of 

 the fry and vv^eaken them so that they readily fall victims to 

 the voracity of larger fish. Dr. Bangham has shown that 

 heavily parasitized fish are smaller than others belonging 

 apparently to the same hatch, so the effect is not mere sup- 

 position. 



By the time the fry are an inch and a half long they have 

 also accumulated some of the round worms, especially the 



i 



