68 Practical Zoology. 



or unfavorable to their development? If possible, learn the rate 

 of growth of fish. 



Fish in Winter. Do fishes migrate ? Are most fishes to be 

 found in the same place, winter and summer? Are they equally 

 active at different seasons? 



AQUARIUM STUDY OF FISHES. 



Respiratory Movements. Watch minnows or goldfish in an 

 aquarium. Note the movements of the mouth and the gill covers. 

 In what order do these movements proceed ? Watch closely to 

 see if there is any water current in connection with these move- 

 ments. If there is no floating matter by which to get evidence of 

 a current, introduce a drop of ink near the fish's head and thus 

 determine the direction of the current. 



Mode of Swimming. How does the fish swim ? Watch especially 

 the slow movements, during which the facts can be more readily 

 learned. What is the main propelling power? How is the course 

 guided? How is the shape adapted for movement in the water? 



Uses of the Fins. Take a light rubber band and pass it round 

 the fish, holding down the various fins in successive experiments. 

 Watch the resulting movements and conditions of the fish. 



How a Fish Floats. Does a fish make effort to maintain its 

 place in water? Does it make any apparent effort in rising or 

 sinking? Do any fishes habitually remain on the bottom? Do 

 any stay at the surface ? Is there any difference in their structure 

 or habits that fits each for its place ? 



Comparison of a Minnow and a Darter. These two forms are to 

 be found in most creeks. In using a minnow seine, be careful to 

 "keep the lead line down" and you will be much more likely 

 to get darters. These are small fishes, with double-cone-shaped 

 bodies. They habitually rest on the bottom. Watch carefully their 

 movements. What takes place when they cease to make active 

 effort? Do they swim in the same way as the minnows? Open a 

 minnow and also a darter to see if there is any essential differei 



