38 NINETKKX'III lU'J'OHl". 



turbt'd tor a icw days bet'orc inti"odiK'iii<>; tlit- animals. This allows the 

 plants to become adjusted to the new conditions and the water becomes 

 thoroughly aerated. 



Too many animals should not be introduced. The amateur aquarist 

 usually overcrowds. A general rule for fish otTered by Page (1898) is 

 three inches of fish to a half gallon of water, Osburn (lOli) is even 

 more parsimonious and suggests one inch of fish, not including the tail, 

 to one gallon of water. The animals should be carefully selected accord- 

 ing to size and habits. P'or this region the black-nosed dace ( Rhinichthys 

 otranasus ) will be found very satisfactory. This species is easy to find, 

 apparently hardy and thrives on prepared fish food. Sunfish or ))umpkin- 

 seeds ( Eupomotis (/ihbostis ) and bluegills (Lepomis pallidum J require 

 meat for food and if not kept well fed will attack both fish and tadpoles. 

 The miller's thumb (Coitus ictalops ) is a shallow water species and will 

 not live long in the ordinary aquarium. Tadpoles, although good 

 scavengers, root up the plants and keep the water more or less roiled. 

 They should be introduced sparingly. Snails are almost a necessity in 

 the aquarium since they are not only good scavengers but also aid 

 materially in keeping the growth of undesirable algae under control. 

 Physa and Planorbis will be found especially satisfactory. They breed 

 readily in the tanks and their eggs and young furnish a limited amount 

 of food for the fish. A dozen or more will be found valuable in every 

 aquarium. Water bugs will prove interesting but they should be care- 

 fully identified before putting them into the tank as many of them are 

 carnivorous and will quickly attack the other animals present. A large 

 number of insects belonging to several orders pass through an aquatic 

 larval stage; some of these are carnivorous while others are vegetarians 

 (Miall, 1895); the necessity of a certain amount of identification is 

 obvious. Hydra t'/r?V//.sv will, under ordinary circumstances, live well and 

 multiply quite rapidly in the balanced aquarium. They are apparently 

 undisturbed by fish and snails and seem to require no food, possibly 

 due to the symbiotic algae which they contain, and the micro-organisms 

 in the water. Colonies of Vortieella are frequently introduced with 

 snails. They multij)ly and spread rapidly and form an interesting sub- 

 ject of study. The fresh water sponge (Spongilla) may also be readily 

 grown from gemmules and although more or less disturbed by fish and 

 especially by tadpoles, may attain a fair size. This form will be found 

 of especial interest because it is so frequently i)assed over unobserved 

 in field work that it is seldom brought into the laboratory. 



It will thus be seen that a great variety of animals may be introduced 

 if care is used in selecting them. They soon accommodate themselves 



