CULTURING OF AMPHIBIAN EMBRYOS 51 



FOOD 

 FOR THE LARVAE: 



Feeding is not necessary for some days after the mouth of the tadpole (larva) is open. 

 This is because all amphibian larvae are provided with an abundance of reserve food in 

 the form of yolk which is digested and absorbed directly by the tissues. 



A. Anura : 



Feeding is not necessary until stage #25. Most Anuran larvae are vegetarians, and 

 the most satisfactory food consists of slightly boiled lettuce or spinach. These 

 greens should be thoroughly washed to rid them of any adherent arsenic or lead 

 which may have been sprayed on them as insecticides by the gardener. Boiling the 

 greens simply softens the plant tissues. The danger, at least in the beginning, comes 

 from over-feeding. The tanks must be cleaned daily to keep faecal and bacterial ac- 

 cumulation at a minimum. For Xenopus larvae cooked, dehydrated, and finely pow- 

 dered beef liver is an excellent supplement to greens, and algae. Liverworst has 

 been used successfully with many Anura. Other foods used are powdered egg-yolk; 

 bacto-beef extract mixed with whole wheat flour, dried and pulverized; raw liver, 

 minced; algae and Protozoa. The lettuce feeding seems to produce fewer abnormal- 

 ities but development is slower than with spinach (Hyman, 1941). Briggs (1942) has 

 shown that a pure spinach diet produces certain minor abnormalities and kidney 

 stones, so that a mixed diet is recommended. On pure lettuce or spinach, or a mix- 

 ture of the two, tadpoles can be reared through metamorphosis with considerable 

 ease. Anura are essentially vegetarian until after metamorphosis, then they are 

 omnivorous with a leaning toward the carnivorous. 



B. Urodela : 



The Urodele larvae require living, moving food. At first, rich cultures of Protozoa 

 and young Daphnia are fed to the larvae after stage #40. The carapace of the older 

 Daphnias will tear the gut of the larvae. The eyesight of these forms is very poor 

 and their neuro-muscular responses are slow, so that the living food must be active. 

 After a week or two of this diet, when the larvae are more hardy, they can tolerate 

 such foods as the red worm (Tubifex), the white worm (Enchytrea), Daphnia (all 

 sizes, but the young ones are better), mealflies, mealworms, wax moths (Galleria), 

 Drosophila (vestigial mutant), plant lice, small ants, and, best of all, amphibian 

 larvae (frog tadpoles of early stages). If not adequately fed the Urodele larvae will 

 tend to nip off each others tails and occasionally larger specimens will devour the 

 smaller ones. Beef liver favors A. tigrinum over A. punctatum while Daphnia and 

 Enchytrea favor A. punctatum over A. tigrinum. Cannibalism is common, and 

 Amblystoma larvae seem to grow best on a diet of Amblystoma. 



If over-feeding is avoided, and any uningested food is removed daily from the tanks, it 

 may not be necessary to change the culture medium more than once or twice each week. 

 As the larvae grow, however, there will appear more faecal material in the tanks, and 

 this should be sucked out with a suction bulb and glass tube or the water should be changed 

 more frequently. The water must not be allowed to become turbid with bacteria. 



FOOD FOR THE POST-METAMORPHIC STAGES: 



After metamorphosis, with correlated changes in the histology of the digestive tract, the 

 food requirements become radically different for all amphibia. Not only must there be 

 more food, but it niust represent a greater variety and should contain vitamins. 



