1 6o A BIOLOGY OF CRUSTACEA 



is generally regarded as an excellent food for goldfish. The keen 

 aquarist can easily culture his own stocks of Daphnia to provide an 

 occasional treat for his pets. The easiest method is to keep water 

 snails and feed them on any waste greenery that they will take. 

 The faeces produced by the snails make excellent food for 

 Daphnia, which will thrive in a tank well stocked with snails. An 

 alternative is to keep axolotls which are fed on earthworms. If a 

 glass tank containing axolotls is stood near a window there will 

 be an abundant growth of microscopic algae which will form a 

 good food for Daphnia. A separate tank is necessary for the water 

 fleas because if kept with the axolotls they will be snapped up and 

 eaten. Every day or two a sample of green water from the axolotl 

 tank should be poured into the Daphnia tank and then replaced by 

 fresh water from the tap. In this way a continuous culture can be 

 maintained right through the winter. 



Daphnia is also dried and sold in packets as fish food. One 

 important centre of this minor industry is in northern Italy. This 

 is believed to date from the time when Bologna goldfish were 

 highly esteemed and the water fleas were used to sustain the fish 

 while they were transported home by tourists. 



The brine shrimp, Artemia salina, is another crustacean used by 

 aquarists. The resting eggs (see p. 72) are sold in small tubes, with 

 instructions how to make them hatch. The nauplii which emerge 

 are used as food for tropical fish. Drying and packing these eggs is 

 a profitable business in North America, where, in certain localities, 

 particularly around the Great Salt Lake, eggs can be collected by 

 the shovelful. The small tubes, containing about a teaspoonful, cost 

 about half a crown to buy in a shop, but even a small tubeful of 

 eggs will provide several thousand nauplii. These nauplii can be 

 reared through to adults if they are kept in sea water and fed on 

 small amounts of yeast which has been stirred up well in water 

 before being poured in with Artemia. 



If sea water is not available a substitute can be made from 

 Tidman's sea salt, which can be purchased from any chemist's. 

 About four ounces of salt to six pints of water will produce a 

 suitable concentration for rearing Artemia. 



When kept in a warm room Artemia becomes mature in about 

 three weeks and will then start to produce nauplii. These can be 

 fished out with a small net and used as fish food while the stock is 

 maintained by further production of nauplii by the adults. A 

 regular supply of fish food can be maintained by judicious manage- 



