PROCEEDINGS OF SECTION D. 289 



times one of the best death-traps for the fishes that one could devise. 

 Particles of food and excrementitious matter collect at the bottom 

 (and this will happen to some extent in the best regulated ponds) and 

 there they lie, corrupting the lower stratum of almost unchanged water — 

 a constant menace to the trout. Should a few of the trout die and lie 

 on the bottom, the defiling and death-dealing influences are much 

 greater, as there is nothing, perhaps, in ordinary fish-culture, that 

 poisons the water in a pond more quickly than a few dead fishes. In 

 ponds constructed on this plan, a fish has but little chance should it 

 become a little sickly. Should it by any means be unable to keep to 

 the surface it simply has no chance of recovery, as it sinks to the foul 

 water at the bottom, there to be quickly overcome. 



The simple contrivance to be described (which has been installed 

 in the trout-ponds of the New South Wales Department of Fisheries 

 at Prospect) was designed for the purpose of constantly drawing off the 

 water from the bottom of the pond, so that there never could be any 

 stagnation or saturation of the water with noxious gases arising from 

 the decomposition of the matter on the bottom. The ponds mentioned 

 which are five in number, are of the following dimensions : — Nos. 1 and 

 2, 30 feet long, 10 feet wide, and 5 feet deep ; No. 3, 40 feet long, 15 feet 

 wide, and 5 feet deep ; Nos. 4 and 5, 60 feet long, 24 feet wide, and 

 7 feet to 2^ feet deep {i.e., 7 feet in the centre, tapering to 2 J feet at 

 each end). 



Nos, 1, 2, and 3 were constructed in 1896, They are quite rect- 

 angular, and of equal depth throughout, and are, therefore, not very 

 satisfactory as live-fish holders. The tendency in such ponds is always 

 naturally towards a certain stagnation of the water, which prior to the 

 introduction of the outflow-boxes to be described in the ponds mentioned, 

 ran in at one end quite at the surface, and then drained away through 

 fine brass-gauze screens again at the surface at the opposite end. It 

 wUl strike an observer at once that these screens of fine gauze, through 

 which the whole water supply had to pass, would very easily clog even 

 with the dust which would blow in at the surface, and such in fact 

 was the case, and constant attention was necessary if the screens were 

 not to be allowed to dam the water up and cause it to flow over the 

 sides of the ponds. In the construction of ponds 4 and 5 in 1901 a 

 much better plan was followed. Here the outline is nearly elliptical, 

 and the bottom gradually shallows towards each end. Still, the ideal 

 has hardly been reached, while, as in other ponds, the water entering at 

 the surface had to filter through the surface screen at the opposite end. 

 Before installing the outflow-boxes, I obtained a great deal of relief 

 from the choking of the screens by putting in leaf screens. These 

 were arranged like three sides of a box, half immersed in the water, so 

 that the latter had to pass under to get to the screens, thus holding 



6117. K 



