PROGRESS IN BIOLOGICAL INQUIRIES, 1936 55 
years that production of food organisms is greater in ponds contain- 
ing vegetation than in those without an appreciable growth of higher 
plants. In the former the average weight of food organisms per 
square meter was 13.68 @ while in the latter is was only 6.48 g. The 
presence of forage fish” (sunfish) in the ponds was found to in- 
crease the survival of bass fingerlings 12.3 percent over that in the 
same kind of ponds without forage ‘fish. ‘The ponds at Marion are 
new and at a low stage of ecological development. Consequently, 
they are much less productive than ponds that have been in use for 
some time. Mr. Meehean estimates that it will require about 3 years 
to develop an adequate permanent fauna in these ponds. 
FISH DISEASES 
A hitherto unrecognized form of gill disease broke out in May — 
among smallmouth bass in a rearing pond at the Leetown station 
and caused considerable mortality before its true nature was dis- 
covered, ‘The losses occurred among brood fish and fry at about 
the time the latter were rising from the nest. The trouble was traced 
to an infection of the gills with a protozoan belonging to the Dendro- 
somidae, a family of Suctoria. This o organism occurs on the gills 
in enormous numbers and appears as a somewhat elongated or 
rounded body closely attached to the surface of the lamellae. The 
parasites are about 30u to 40u in diameter and usually show a dis- 
tinct orange color. In heavily-infested bass the outer ends of the 
gill filaments become enlarged and club-shaped. Later the swollen 
ends become necrotic and fungus develops, forming a mat of felted 
fibers to which cling particles “of silt and debris, giving the appear- 
ance of a dirty white mass attached to the ends of the gill filaments. 
Eventually a considerable area may become necrotic, resulting in the 
death of the fish. Later in the season the same parasite was found 
on the gills of bass which were suffering a heavy mortality at a 
hatchery i im Maryland. 
Investigations of diseases among salmon and trout were conducted 
by Dr. Frederic F. Fish at the recently established pathological 
laboratory at Seattle, Wash. Experiments to determine the effect on 
fish of the use of disinfecting solution at regular intervals were con- 
ducted at the Birdsview, Wash., and Clackamas, Oreg., hatcheries. It 
was found that certain concentrations of disinfectants could be 
safely used on salmon and trout from egg to fingerling stages without 
risk of incurring any greater mortality than was encountered in the 
untreated control lots. In some instances the loss on treated lots was 
definitely lower than on the untreated lots although no specific dis- 
ease was present. The maximum safe concentrations’ for weekly apph- 
cations under the conditions at these hatcheries was found to be: 
Malachite green, 1: 450,000; sodium dichromate, 1: 125,000; chlora- 
zene, 1: 150, 000. Potassium permanganate, even as dilute as 1: 400,- 
000, "appeared to be distinctly toxic and the effect appeared to be 
cumulative. 
After 12 months of experimentation, the impracticability of per- 
forming experimental work at routine hatcheries became so obvious 
that. further work was dropped pending the construction of a small 
experimental hatchery that could be entirely devoted to this purpose. 
With the cooperation and financial assistance of the Division of Fish 
