EXPERIMEHTAL FISH EMBRYOLOGY 56I 



Some vegetation Is good for the tank, but when an aquarium Ib so green that the fish 

 cannot he seen, it is a sign of contamination resulting from too much light. The so-called 

 BCavangers such as snails, fresh water flounders, catflshes, loaches, and tadpoles, will 

 help to keep the vegetation down hut the hest method is to reduce the light ration. 

 Plants that supply abundant oxygen help materially to keep the tank clean. 



The best scavangers are the moss-back snails. Small, live-bearing snails are better 

 than the larger and often more colorful snails. It should be stated, however, that while 

 no snails eat living fish or fish fry, some snails will damage fish eggs. There are fun- 

 gus spores in all aquaria but these will never attack healthy fish. 



AQUABIUM WATEB : 



Never use distilled ore rain water as these do not contain the necessary minerals. 

 Conditioned tap water is best. Fill the tank 2/5 full of warm tap water (the wanning 

 helps to drive out any chlorine or other toxic gases) and let it stand until the water is 

 cool. Place sterilized sand or gravel in the back comers of the tank, plant such vegeta- 

 tion as is suitable (see below) and slowly siphon in additional tap water. In a 5-gallon 

 tank the water should have a depth of about 5-6 inches. Let this tank stand in sunlight 

 for 1 day, or aerate for a similar period. Metal frame tanks of 5-gallons or more should 

 not be moved after filling because the weight of the water plus the strain on the frame 

 will cause leaks. See that all tanks are evenly and adequately supported before adding 

 the water. Evaporation is balanced by adding distilled water to the original level at 

 least once each week. 



The pH of the water should be near the neutral point (6.8-7.2). Some fish breed 

 better when the water Is lightly acid (6.8) and others when It Is slightly alkaline (7.2). 

 The addition of chalk, plaster of Paris, or other so-called neutralizers is ill-advised. 

 If the pH must be very accurately controlled this should be done with harmless phosphate 

 buffers and the water tested by colorlmetrlc or electrical pH determinations. 



The temperature of the water needs to be regulated for the tropical fish and for 

 those whose breeding reactions depend somewhat on ten^ieratures. Regulation Is best by 

 thermostat and electric heater. These are the only metal structures that ever come in 

 contact with aquarium water, and they are protected since even the slightest amount of 

 copper or selenium is toxic to fish. The temperature range for fish is 70° - 85°F, , the 

 breeding temperatures being the higher ones. In fact, one of the methods of regulating 

 breeding (of the tropicals particularly) is to keep the fish for a period at the lower 

 level of the tolerance range and then elevate the temperature to 80° - 82°F. when they 

 will generally breed. It is most important to regulate the temperature during the period 

 from October to April when the laboratory temperatures are generally below the tolerance 

 range or are somewhat variable. 



Aeration of water when the fish are in it is generally accomplished by appropriate 

 vegetation. Two functions of plants are to add oxygen and to release toxic gases. Arti- 

 ficial aeration is not necessary in a properly balanced aquarium but should be provided 

 where colonies of fish are likely to deplete the normal supply of oxygen or where the 

 light is insufficient to maintain the plants. Artificial aeration is particularly harm- 

 ful to fish fry which are extremely delicate and are damaged by the air bubbles and excess 

 currents of water. 



AQUABIUM LIGBTIHG : 



The most uniform lighting is that from the northern skies, without direct sunlight. 

 Aquaria may be exposed to direct sunlight but for not more than 1 hour each day. Continu- 

 ous artificial lighting may upset the normal fish cycles since many fish actually sleep 

 and some seem to carry on maturatlonal processes during the night and oviposltion during 

 the day, e.g., Oryzlas. The best conditions are attained if the background behind the 

 tank is light (white cardboard) and a 50-75 watt bulb is placed above and toward the front 

 of the tank with reflector throwing the light toward the back of the tank away from the 

 observor. The bulb should be at least 8-12 Inches away from a 5-gallon tank and the light 

 should be on for an 8-hour day. If the aquarium becomes discolored with an abundant 

 growth of algae, reduce the light ration. 



