COPEPOD PARASITES AND MUSSEL GLOCHIDIA ON FRESH-WATER FISHES. 347 



all the time, and thus the copepods are shut out. This leads to the conclusion that when 

 a fish's gills are artificially infected with glochidia the fish is thereby rendered immune 

 to the copepods. Artificial infection therefore, as regularly practiced at the biological 

 Station, not only does the fish no harm but is even positively beneficial. 



And this suggests a possible safeguard or remedy for some fish hatcheries. It occa- 

 sionally happens that parasitic copepods get to breeding in a hatchery in such numbers 

 that they kill the fish. Judging from the cases thus far reported, this seems more 

 likely to occur among trout than among other game fish. The European trout {Salmo 

 fario Linnaeus) is the natural host of Margaritana margaritifera, but our American trout 

 have been examined very little for glochidia. However, if there is any ^'irtue in the 

 conclusions here drawn, the very fact that they are more susceptible than other fish to 

 the copepod parasites indicates that they would make excellent hosts for glochidia. 

 If this be so, an infection with glochidia would be harmless to the fish, but at the same 

 time would render them immune to the copepods. At all events, the experiment is 

 worth trying. 



4. The breeding season of the copepods thus acquires especial economic importance 

 with reference to mussel propagation. It is manifest that at the close of a breeding 

 season, when the larval brood of copepods have sought and found their hosts, their 

 numbers will be at a maximum. Consequently this would be the time least favorable 

 to infection with glochidia. On the other hand, the early spring, before the copepods 

 begin to breed, and the intervals between successive breeding periods, would be the 

 most favorable to glochidial infection. 



We are not yet sufficiently acquainted with either kind of parasite to be able to 

 make a complete schedule of their times of breeding, but many interesting facts have 

 been ascertained. 



Lefevre and Curtis in the Bulletin of the Bureau of Fisheries, volume xxx, page 141, 

 divide mussels into two groups according to the length of the period of gravidity. Those 

 having a long period of gravidity, among which Lampsilis species predominate, produce 

 ripe glochidia during the fall and winter and spring months. Those having a short 

 period of gravidity, among which Quadrula species predominate, produce ripe glochidia 

 during the summer months. Turning now to the copepods, we find that the ergasilids 

 and argulids have three breeding seasons in the year, the first at the end of May or the 

 beginning of June, the second at the middle or latter part of July, and the third in the 

 latter part of September. We do not yet know all the breeding seasons of the lernaeids 

 and lernaeopods, but from the material here presented and that obtained from many other 

 investigations it is certain that they also have a breeding season during the middle or 

 latter part of July, and it is probable that there are two other seasons corresponding to 

 those just given. 



Comparing the breeding of the copepods with that of the mussels, it will be seen 

 that the winter or early spring is the best time for infection with Lampsilis glochidia, 

 since the only copepods then on the fish's gills are such adults as have lasted through 

 the winter. None of the Quadrula group produce glochidia early enough to be used 

 for spring infection, and the best months for them would be July and September, just 

 before the second and third copepod breeding seasons; and from what has already been 

 said of the cumulative efifects of unfavorable conditions during low water the month of 

 July would ordinarily be preferable to September. 



