346 CARE AND FEEDING OF LABORATORY FISH 



Some fish are naturally dirtier than others (e. g. , Hemichromus, Tulapia) and it will be 

 necessary to siphon off the faecal material and uningested food almost daily. If aerators 

 are used, they must be shut off and the debris allowed to settle for a time before siphon- 

 ing. If the aerators themselves become clogged with debris and vegetation they should be 

 removed and cleaned by dipping them in acetic acid or vinegar, and rinsing. 



Some vegetation is good for the tank, but when an aquarium is so green that the fish can- 

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

 scavengers such as snails, fresh water flounders, catfish, loaches, and tadpoles, will 

 help to keep the vegetation down but the best method is to reduce the light ration. Plants 

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



The best scavengers 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 fungus 

 spores in all aquaria but these will never attack healthy fish. Scavengers are not really 

 necessary in a perfectly balanced tank, where there is no overfeeding. 



AQUARIUM WATER: 



Never use distilled or rain water as these do not contain the necessary minerals. Con- 

 ditioned tap water is best. Fill the tank 2/3 full of warm tap water (the warming 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 corners of the tank, plant such vegetation 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 3 -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 slightly 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 buf- 

 fers and the water tested by colorimetric 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 temperatures. 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. Glass heaters with thermostats are readily avail- 

 able. 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 par- 

 ticularly) 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 vari- 

 able. 



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

 etation. Two functions of plants are to add oxygen and to release toxic gases. Artificial 

 aeration is not necessary in a properly balanced aquarium unless it is overcrowded but 

 should be provided where colonies of fish are likely to deplete the normal supply of 



