400 BULLETIN OF THE BUREAU OF FISHERIES. 



heal over; but in the process of mending the glochidium is overgrown and thus inclosed 

 within the tissues of the fish. The mussel is now actually an internal parasite, in 

 which condition it remains for a period of two weeks, more or less. It is thus con- 

 veyed wherever the fish goes, until, when the proper stage of development is reached, 

 it frees itself from the host and falls to the bottom ; if through favorable fortune it finds 

 suitable lodgment, it continues its growth to form an adult mussel." 



The glochidia are so small that the infection, if not excessive, has no apparent 

 injurious effect upon the fish that serves as host. Investigations by the station have 

 shown that mussels do not attach to fish indiscriminately, but that for each species of 

 mussel there is a limited number of species of fish which may serve as host. Particular 

 instances are mentioned on a later page. 



The task of propagation is to bring together suitable fish and the glochidia of mus- 

 sels. Careful studies of natural and artificial infections show that a moderate sized fish 

 may successfully carry in parasitism from i,ooo to 2,000 of the microscopic glochidia, 

 but that under the chance operation of nature few of the glochidia find a lodgment upon 

 the proper fish or upon any fish. 



During the last fiscal year, in round numbers, 344,000,000 glochidia were liberated 

 in parasitic condition, 208,000 fish being employed in the operations. A considerable 

 proportion of these glochidia undoubtedly fall upon unfavorable ground or from other 

 causes fail of reaching maturity. However, it is the large number which can be 

 infected and liberated at small expense that justifies a confidence in the accomplishment 

 of commensurate benefits. The average cost per i ,000 glochidia artificially infected in 

 the fiscal year 1915 was 2.7 cents, inclusive of overhead expenses. 



METHODS OF PROPAGATION. 



The operation of infecting the fish with glochidia is a very simple one, though the 

 methods may vary considerably with each party. Essentially the method is as follows: 



(i) The first step is to secure a number of gravid mussels in order to obtain a supply 

 of glochidia. Generally this can be accomplished by visiting the beds where mussel 

 fishermen are engaged in work, looking over the catch, and picking out the desired 

 number of gravid females, for which a small sum may be paid. 



(2) These mussels are then opened, the marsupial passages are cut out, placed in 

 a pan of water, where they may be opened witli scissors or scalpel and the glochidia 

 squeezed out into the water. The glochidia are taken up with a suitable pipette and 

 placed in a small container, such as a glass or can. Usually this operation is delayed 

 until the fish have been obtained. 



(3) It is now necessary to secure as many fish as possible by means of seine or 

 nets, and the species of fish must be appropriate for the species of mussel to be propa- 

 gated. (See pi. Lxxix fig. 8-10.) After the fish are transferred from the seine to tubs 

 or tanks, and when a suitable number of fish are in the tanks, overcrowding being 

 avoided, a lot of glochidia are thrown into the water. (See pi. lxxix, fig. 11.) There 

 is no definite rule as to the number of glochidia to be used with any number of fish, 

 but the person in charge is guided by his experience with due regard to the temper- 



o There are one or two species of mussels which need not attach to fish, but these are of no commercial value. There are a 

 few species which during the period of parasitism increase in size manifold, being true parasites; but the greater number of species 

 are between these two extremes, using the fish for conveyance and protection, but certainly deriving no considerable amount 

 of nourishment. 



