28 Proceedings of Royal Society of Edinburgh. [sess. 
salmon being 51 lbs. On 6th July of this year (1903) seven bull 
trout were weighed together, and turned the scale at 214 lbs., 
showing the high average of 30 lbs. A small run of fish between 
5 lbs. and 8 lbs. appeared with the grilse in July ; and I may remark 
in passing that the Tay grilse are heavy as compared with the 
grilse of other rivers. 
In general outline this so-called bull trout is in no way different 
from the shapely Tay salmon, and the appearance of the head, 
the outline of the gill cover, and shape of the preoperculum are 
identical. This is seen in PI. fig. 1. The caudal fin also and the 
caudal peduncle are alike in like sizes of fish. The opportunity 
given me of viewing salmon interspersed with bull trout laid out 
in rows upon the sloping cement floor of the Tay Fisheries Co. 
Fish House at Perth enabled one not only to compare bull trout 
and salmon, but to note the variations which occur in "both ; and 
those variations I found to be in no way dissimilar. 
The distinguishing feature of the bull trout is primarily one of 
surface marking. The dorsum is more or less thickly speckled 
with small black spots, and these are also to a varying extent 
displayed on the side, and more especially on the ‘shoulder’ of 
the fish below the lateral line. A well-marked bull trout has 
the spots below the lateral line continued backwards as far as the 
level of the dorsal fin. But when one examines a large number 
of fish, examples are readily found with few spots ; and one notices 
that a diminishing gradation blends ultimately into an appearance 
which in no way differs from that seen in fish which are unquestion- 
ably pure salmon. 
A peculiar characteristic of these fish, however, is the presence 
of ‘maggots’ (Lerneopoda salmonea, Linn.) on the gills, the parasite 
which commonly infests the gills of salmon kelts in fresh water. 
These bull trout coming from the sea into the river, and with tide 
lice (Lerneopthirus) upon them to prove their comparative clean- 
ness, are nevertheless usually infested by gill maggots. 
I know of no other special features other than the two just 
mentioned whereby this so-called bull trout may be distinguished 
from salmon, and in my opinion no real structural difference 
exists. 
A detailed examination reveals nothing in the dentition, fin-ray 
