18 



aquatic Hit 



them on the gills or fin of a fish, where 

 they are firmly attached by hooks. They 

 remain attached as parasites on the fish 

 for some weeks (in some cases, months) 

 and undergo further development. After 

 leaving the fish they are still not fully 

 formed, as they take about three years to 

 obtain all their gills, and another two 

 years before they are sexually mature, 

 growth continuing all the while. Usually 

 the various species of mussels have par- 

 ticular fish, or families of fishes, as hosts, 

 only upon which the glochidia will grow. 

 They will attach themselves to most any 

 fish that touches them, but will fall off 

 from all but their proper hosts. Profes- 

 sors Needham and Lloyd, in the "Life 

 of Inland Waters/' say that "The part 

 taken by the fish in the association is 

 truly remarkable. The fish is not a mere 

 passive agent of mussel distribution. Its 

 tissues respond to the stimulus of the 

 glochidia in a way that parallels the re- 

 sponse of a plant to the stimulus of a 

 gall insect. As the plant develops a gall 

 by new growth of tissue about the attack- 

 ing insect, and shuts it in and both shel- 

 ters and feeds it, so the fish develops a 

 cyst about the glochidium and protects 

 and feeds it. The tissues injured by the 

 valves of the glochidium produce new 

 cells by proliferation. They rise up about 

 the larva and shut it in. They supply 

 food to it until the metamorphosis is com- 

 plete, and then, when it is a complete 

 mussel in form, equipped with a foot for 

 burrowing and with a good system of 

 nutritive organs, they break away from it 

 and allow it to fall to the bottom. Since 

 this period lasts for some weeks, or even 

 in a few cases, months, the fishes by 

 wandering from place to place aid in the 

 distribution of the mussels." The glo- 

 chidia seem to do little or no harm to the 

 fish. The cysts are eventually cast off 

 and leave no scar. 



In conclusion it must be stated that not 



all mussels have a life-history agreeing 

 with the foregoing outline. A few spe- 

 cies are not parasitic and develop to the 

 adult form in the brood chamber of the 

 parent. 



Unio complanatus, a drawing of a 

 valve of which is reproduced by permis- 

 sion from Frank L. Tappan's "Aquaria 

 Fish," is a very common species which 

 occurs in almost every stream and river 

 on the Atlantic slope. The shell is usually 

 a yellowish-green in young specimens and 

 brownish-green when mature. A full 

 grown individual will measure three 

 inches long, two inches broad, and one 

 inch thick near the hinge. This Unio is 

 an active mussel, often moving several 

 inches in a day. It is an interesting scav- 

 enger and if placed with compatible fishes 

 will live in the aquarium for years. 



The Aquarist Avoids 



Changing the temperature of the water, 

 carrying about a fitted aquarium, placing 

 beetles or water spiders in the aquarium 

 with fishes, putting sea shells, corals or 

 marine specimens in a fresh water aquar- 

 ium, using soap or chemicals to clean the 

 tank (use whiting and salt), throwing a 

 fish into the water, introducing a doubt- 

 ful specimen without quarantining, leav- 

 ing uneaten food to dissolve and pollute 

 the water, tapping on the glass, using a 

 deep, funnel-shaped net, putting the hand 

 in the water unnecessarily, allowing any 

 tobacco from the hand to go into the 

 water, many persons taking care of one 

 aquarium ; small, round glass globes, ex- 

 cept for small tropical fishes, strong sun- 

 light, keeping diseased fishes with healthy 

 ones, needless disturbance of aquarium 

 and contents. 



Now that the hot wave's put to rout, 

 we soon will get together, and kick and 

 cuss as hard about the cold autumnal 

 weather. 



