FRESH WATER ANIMALS: DEPOSITS: AMPHIBIA 



Davis ^* in 1930 claimed that hatchery trout, fed dried salmon eggs 

 showed the same coloration as wild trout of the same age. Mann ^ ' 

 confirmed this using as food goldfish, carrots , and mixed Daphnia spp. 

 The results of McCay and Tunison's^^ experiments were, however, 

 not so clear cut. More recently, Steven 2, 1 2 has confirmed that trout 

 carotenoids are of alimentary origin and has provided a much more 

 quantitative picture of the situation than had previously been available. 



Steven found that trout kept in captivity maintained their natural 

 pigmentation when their diet consisted of natural food supplemented 

 by live Entomostraca (chiefly Simocephalus and Daphnia spp.) and 

 Corethra larvae. When placed on a diet of chopped meat and earth- 

 worms the fish lost their red and yellow pigmentation and their caro- 

 tenoids were reduced almost to zero ; these trout when transferred 

 to a diet of salmon eggs rapidly assumed their original coloration and 

 after 35 days their carotenoid content was back to its original level. 



Table 37 — The Effect of Diet on the Carotenoid Content of the Brown 



Trout 

 From Steven, D. M., (1949) J. exp. Biol. 26, 295. 



Steven attempted to produce carotenoid pigmentation by feeding 

 earthworms previously injected with either [B-carotene, lutein (xantho- 

 phyll), or astacin dissolved in arachis oil. No increased pigmentation 

 was observed in any of the diets. The failure was attributed to failure 

 of the fish to deal adequately with the comparatively large amounts of 

 oil in the diet although Lovern^^A states that fish absorb fat well. 



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