206 Phylum Arthropoda 



will sink and some will float. The former are nearly 100% viable. A 

 majority of the floaters will also hatch, but the percentage of viability will 



be smaller. 



For transportation, young Artemia must be placed in open contain- 

 ers, since they are very susceptible to accumulated C0 2 . 



The hatching medium may be almost any salt solution not containing 

 much potassium, and ranging in concentration from about 0.1% to 6%. 

 Natural or artificial seawater is as good as anything. After hatching, 

 the nauplii may be transferred directly into more concentrated solutions, 

 but in the higher concentrations the mortality may be great unless the 

 change is made gradually, either by stages or by evaporation. Older 

 animals are much less resistant than nauplii, and are killed by large 

 changes in concentration of the medium, unless the changes are very 

 gradual. When a culture is established it is continued by viviparous 

 reproduction. The first batch of eggs produced by the females usually go 

 at once to the nauplius stage in the brood pouch and then escape. Subse- 

 quent batches of eggs from the same females are resting eggs and must 

 be dried before hatching. Under most favorable conditions, a generation 

 takes about 3 weeks. 



It is possible to raise the animals in a wide variety of salt mixtures, from 

 about 4% to concentration, always provided that the concentration of 

 potassium is not too high in proportion to other salts present. For getting 

 the animals to reproduce as rapidly and as vigorously as possible, I 

 have found nothing better than seawater with 5 to 8 gm. NaCl per 100 cc. 

 added. Artificial aeration of cultures in unfavorable media is helpful. 



For food, particulate matter is required. Ordinary yeast is excellent 

 and convenient. It should be suspended in enough freshwater to make 

 up for evaporation and floated on the salt medium. For starting cultures, 

 however, and for unfavorable media, a rich culture of a one-celled green 

 alga such as Dunaliella salina, D. viridis, or Platymonas subcordaeformis 

 will be found very helpful. [For culture see p. 134.] Food should be 

 added in small quantities every day or two. 



The optimum temperature is about 30 C, but Artemia will live at 

 temperatures as low as io° and as high as 37 . 



Reference 

 For the culture of Artemia see also p. 215. 



