118 BULLETIN OF THE BCREAI' OF FISHERIES. 



vicinity of Woods Hole, and give with them a list of the hosts upon which they are 

 found, their breeding seasons, and such additional facts as may be of general value. 

 They can thus be presented in a more compact form and one easier of reference for 

 the working naturalist. There has also been included a description of the eggs and 

 emerging larvae, so far as known, for identification when found in the tow or (in the 

 ease of the eggs) upon the surfaces where they have been deposited. 



There is good reason for supposing that all the species have three breeding seasons 

 a year, but however that may be, the dates here given are those actually known from 

 eggs deposited in aquaria or from females obtained full of ripe eggs. Most species 

 occur upon the external surface of the fish's body and may usually be found near the 

 tins or the operculum, but a few live within the gill cavity and are seldom found any- 

 where else. These localities have been indicated under the separate species. 



This family often becomes important economically as a factor in the propagation 

 and life history of our common food-fishes, especially fresh-water forms. Ordinarily 

 the Argulida roam about so freely as to occasion little discomfort to their hosts. 

 Thev change frequently from one species of fish to another, and must of necessity 

 desert their hosts at the breeding seasons, since their eggs are deposited upon some 

 convenient surface at or near the bottom, and are not carried about with them. Any 

 fish, therefore, no matter how badly it may be infested, has a chance three times a year 

 to get comparatively well rid of its argulid parasites. Furthermore, under ordinary 

 conditions only a few specimens will be found upon a single fish, and these probably 

 do not occasion any greater discomfort than the fleas upon a cat or dog, and they 

 certainly do not menace the life of the tish in the least. We must not forget, also, 

 that these parasites, like every other creature, have active enemies, and at certain 

 critical periods in their development they also find serious obstacles to overcome. 

 Thus the great majority of them ate destroyed and they are kept within due bounds. 



Let any of these conditions change, however, and the whole situation is 

 reversed. If a tish for any reason becomes inert or debilitated the influence of the 

 parasites is increased, and they may effectually prevent recovery and thus become 

 at least the indirect cause of death. While tin' great majority of the Arguli prefer 

 a sound, healthy fish, there are some species that seem to congregate upon diseased 

 individuals. This is especially true of Argulus megalops, and almost every specimen 

 of a summer or winter flounder that is diseased when captured will yield a harvest 

 of this species. Yet even here we need to remember that the diseased condition is 

 the cause and not the effect of the presence of the parasites. 



Again, surrounding conditions may become, unfavorable to the fish, but not 

 particularly so to the parasite, thus weakening the resistance of the host. A change 

 of this sort always takes places when migrating tish leave the salt water and ascend a 

 river or stream for the purpose of spawning. Of course stationary parasites are 

 taken along with their host as a matter of necessity, but it has also been satisfac- 

 torily proved that many species of Argulus can live in fresh as well as salt water and 

 probably accompany their host as a matter of choice. As the fish gradually succumb 

 to the rigors of migration the pernicious effect of the parasites is increased twofold. 

 In the first place all the fish are weakened by the tremendous effort required and 

 the accompanying abstinence from food, and therefore would feel the irritation 

 more: and then as fast as any of the fish die these free-swimming Arguli can congie- 



