PnuiLLiPPS.— Food-supply and Deterioration of Trout. 381 
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Food-supply and Deterioration of Trout in the Thermal Lakes District, 
North Island, New Zealand. 
Ву W. J. Рниллррѕ, F.L.S., F.R.G.S. 
[Read — = ван dar apis Society, 3rd August, 1921; received by Editor, 
issued separately, 8th July, 1924.) 
INTRODUCTION. 
Tue following paper comprises a section of the results of an investigation 
on trout food-supply and trout-deterioration, together with a brief notice 
of other works on these subjects published in various parts of the world. 
Food-supply for trout is largely dependent on | local conditions, and it is 
locality. Owing to continuous destruction of trout food by the Maori, and. 
the presence of various aquatic birds, the study of this subject may become 
considerably involved. The birds may 190; either on the enemies of the 
trout or the trout themselves, or may in various ways lessen the available 
food-supply. Accordingly a general dives of the habits of the birds 
becomes necessary, and also a consideration of the relative depredations 
of each species. 
have been able to conduct an investigation over a limited period 
only, and realize that the results so obtained cannot be regarded as fully 
conclusive. Generally speaking, large lake trout were found to be feed- 
ing on fishes, while stream and many inshore trout were found to prefer 
insects, crayfish, plants, &c. Microscopical slides i stomach-contents 
were taken нейи к. capture of the trout, for as a rule the 
digestive fluid acts quickly on unicellular окан, га and renders their 
outline indistinguishable. Except where otherwise signified, all trout dealt 
with belonged to the rainbow series, and were over two years of age. 
I wish to thank Messrs. W. R. B. Oliver and H. Hamilton for 
their co-operation in determining certain of the raum in the table. 
Mr. Oliver assisted by identifying a number of the plants, while Mr. 
eem examined the insects. I have also to acknowledge my indebted- 
ness fessor H. B. Kirk, Аланд, University College, Wellington, 
for his interest and kindly criticisms. Further, my thanks are due to 
those бт in the Rotorua district who assisted me in securing is 
for examination 
SUMMARY OF ÁNALYSIS OF Trout STOMACH-CONTENTS. 
Altogether 89 trout-stomachs were examined, the contents of which 
may be summarized as follows: 56 contained fish or fish- -remains ; 32 
contained insects or insect-larvae ; 17 contained molluscs; 11 contained 
cra ; 9l contained plants; 44 contained microscopical organism 
33 had stones, sand, or gravel in stomach or intestine ; 8 contained the 
parasitic worm Histrichus sp. 
