300 CIVIC BIOLOGY 



which the plants require for healthy growth. The common 

 mistake of beginners is to overcrowd the aquarium with both 

 animals 'and plants; more waste matters are produced than 

 are continuously used, and bacteria develop and foul the water. 

 Too much light is the other common danger ; this results in 

 the excessive growth of algae, which green the water and 

 overgrow the glass. A pond receives light only from above, 

 while the aquarium may be lighted from the sides as well. 

 Hence aquaria do better in north or east windows, and even 

 here must be provided with cardboard shades to shut out 

 almost all direct sunlight from the sides. South and west 

 windows may be used if three sides are shaded and the 

 top partially shielded from direct sunlight if alga 1 become 

 troublesome. Great care must be exercised not to overfeed, 

 because uneaten food will decay and quickly foul the water. 

 In an aquarium properly planted with good oxygenators 

 temperature of the water not allowed to go over 15 18 

 (60 65 F.) -two fishes 3 inches long per gallon is the rule. 

 Large specimens cannot be made comfortable in small aquaria; 

 consequently small ones must suffice for schoolroom demon- 

 stration and study. Predacious fishes (pickerel, basses, and 

 sunfish, eels, and all except the smallest catfishes) should 

 ordinarily be kept, each kind and usually each size, in a sepa- 

 rate aquarium ; and it will be necessary to watch them and 

 to remove any vicious specimen or to partition it oft' with a 

 pane of glass. In equipping a laboratory or in planning an 

 exhibition it is better to have a considerable number of small 

 and medium-sized aquaria easy to set up and each with its 

 own distinct and clearly labeled exhibit than to have a few 

 cumbersome aquaria with impossible or difficult combinations 

 mixed up in them. 



The temptation is to make aquaria too big. Taking the dimensions 

 given on page 14, we have the following data for approximate capacity 



