PLANTS AND OTHER CONSIDERATIONS 55 



ficient light is present. V. americana grows more rap- 

 idly and makes a larger plant than V. spiralis. 



The Amazon sword plant ( Echinodorus rangeria ) is 

 a broad-leafed plant that requires a substratum. It 

 reproduces slowly, but each plant reaches a size of a 

 foot or more in diameter. In general, it is a more ex- 

 pensive plant. Under good conditions it puts out run- 

 ners which can be rooted with ease. 



Control of Reproduction 



When held at the proper temperature and ade- 

 quately fed, many of the small fishes will reproduce 

 in aquaria without any special inducement. Some 

 fishes will satisfactorily develop gametes but fail to 

 actually spawn. StiU other species will not develop 

 eggs under aquarium conditions. Some fishes can be 

 stripped, while others can be stripped after a prelimi- 

 nary injection of pituitary. In addition fighting be- 

 tween sexes and egg and fry eating add to the com- 

 plexity of the problem of getting fishes to successfully 

 reproduce in captivity. Some of the techniques for 

 deaHng with these problems are discussed below. 



The development of gametes and spawning are 

 under the control of hormonal products produced by 

 the pituitary gland. The pituitary in turn is stimulated 

 by light and temperature. In addition, proper nutri- 

 tion and freedom from crowding (Swingle 1956) are 

 essential for the development of the gametes. If 

 gamete development and spawning cannot be ob- 

 tained by adjustments of food, light, temperature and 

 population density, it is possible, at least in numerous 

 species of fishes, to induce both by injections of pitui- 

 tary products. To stimulate gamete production a 



