A. E. Shipley 
191 
Certain trout found in the streams on the estate of the Hon. Sydney 
Holland, Royston, Herts., have been dying off in considerable numbers 
during the spawning season for the last year or two. Some of these 
were sent to Cambridge this spring, and, on dissection, it was found 
that the cavity of the swim-bladder was infested with Nematode worms 
of the species described under the name A. cystidicola by Schneider, 
now re-called C. farionis. 
In his original description Fischer draws attention to the curious 
atmosphere it which the worm lives. He describes the gas in the swim- 
bladder of the trout as being almost pure nitrogen with a little C0 2 . 
Whether a more recent analysis of the gas from this fish’s swim-bladder 
has been made I do not know but as a rule in fresh-water fishes, to 
quote Gunther, the gas “consists of nitrogen with a very small quantity 
of oxygen and a trace of carbonic acid.” The pi’oportion of oxygen is 
usually greater in sea-fishes and it also varies in the same fish at 
different seasons. Bunge (1890) has shown that Ascaris mystax from 
the intestine of the cat can live for four or five days in an atmosphere 
quite free from oxygen and that in a similar medium A. acus from the 
pike will live and move for from four to six days. Probably the traces of 
oxygen in the trout’s swim-bladder are sufficient to supply the meagre 
wants of C. farionis. 
The parasites are stated to be more numerous in the winter: in the 
late spring they seem to average 8 to 18 or so in each fish. They have 
also been met with in the oesophagus and probably enter the swim- 
bladder through the “ ductus pneumaticus.” 
The question whether the presence of these parasites is injurious to 
the fish is a debateable one. They are usually regarded as harmless. 
Certainly many of Mr Holland’s trout have been dying but the worms 
were found in the trout before the mortality set in, and in those fish we 
examined at Cambridge they were at least as numerous in fish reported 
as being healthy as in those fish that had died. On the other hand all the 
dying fish appear to suffer from some derangement of the swim-bladder; 
they swim always on the surface on the water and die with their heads 
downwards and the body almost if not quite perpendicular to the surface 
of the water. They die, as Mr Holland tells me, not only in deep water 
but occasionally in the shallow water of the spawning beds. This year 
however during the period of greatest mortality when 6 or 7 trout were 
dying a day until some 50 out of 200 were dead, they never tried to 
work up stream to the spawning beds but died in the deep water. The 
fish seemed to have difficulty about shedding their ova and it may be 
