264 BRITISH FRESH-WATER FISHES 
The grounds for reckoning the trout of Loch Leven as 
a distinct species (Salmo levenensis) have been submitted of 
late years to more searching analysis than has been applied to 
the case of the ferox. Prolonged observation in the Loch 
Leven hatchery and other similar establishments has tended to 
show that, although pure Loch Leven trout maintain their dis- 
tinctive outward character longer than most local varieties of 
trout submitted to novel environment, yet the tendency is to 
assimilate with trout from other waters. The excellent and 
abundant food in Loch Leven, enjoyed for centuries by the fish 
in that favoured mere, has resulted in the establishment of a 
superior variety of trout ; but no such permanent changes in 
structure have taken place as seem to me to constitute a species. 
Loch Leven trout are distinguished by their somewhat slender 
form compared with those in other waters, probably arising 
from the rapidity of growth in consequence of stimulating 
and plentiful nourishment. They are also more silvery than 
most fresh-water trout, with less yellow along the sides of the 
abdomen, and the spots are large and dark, without any scarlet. 
The Gillaroo trout of some of the Irish loughs has been 
classed by Dr. Giinther as a separate species, Sa/mo stomachicus, 
on grounds which appear to me even less tenable than those 
which sufficed for the Loch Leven trout. The sole constant 
difference seems to be that the integument of the stomach is 
three times as thick as that of an ordinary trout, which is 
supposed to arise from this fish feeding to a large extent upon 
shell-fish. Speaking with all diffidence, I submit that there is 
nothing that has been ascertained about these trout to establish 
them as more than well-fed, well-grown specimens of Sa/mo 
fario, attaining the weight of 10 lb., and seldom caught under 
2 Ib. in weight. The same Gillaroo represents the Irish gio/la 
ruadh, red fellow, indicating the orange and rosy tints of the 
skin which distinguish it, when in fine condition, from the 
silvery coated trout which are caught in the same lakes. 
I have already (page 257) ventured to express dissent from 
