1924. Southern. — YV/c l^aiina of a Halchcrv Filler. 135 

 THE FAUNA OF A HATCHERY FILTER. 



BY R. SOUTHERN, B.SC. 



During the present year the sahiion hatchery at Glenties, 

 Co. Donegal, on the River Owenea, now vested in the 

 Department of Fisheries, has been reconditioned and greatly 

 enlarged. In the course of these operations it was necessary 

 to clean out and make certain alterations in the filter 

 through which passes the water-supply for the hatchery 

 boxes. The filter, which is built of brick and concrete, 

 is divided by partitions of the same material into twelve 

 compartments, each 4 feet by 3 feet 9 inches, the depth 

 ranging from i\ to 2\ feet. They are filled w^ith river 

 gravel, the particles of which vary in size from coarse sand 

 to large pebbles. In course of time, a certain amount of 

 fine mud, derived mainly from peat, is deposited from the 

 water in the interstices of the gravel. The water flows 

 from one compartment to the other through openings 

 which are alternately at the top and bottom of the 

 partitions, and the whole filter is loosely covered with sheets 

 of corrugated iron. The water is derived from the River 

 Owenea and is led through a narrow sluice for 20 yards, 

 and then through iron pipes for 35 yards. The intake of 

 the sluice is on the right bank of the Owenea, about 200 

 yards above its junction with the Stracashel River. 



It was on June 19th of this year, after the gravel had 

 been emptied out of the filter and the compartments were 

 still full of water that these notes were made of the fauna 

 which had established itself. The filter had last been 

 emptied and cleaned in July, 1923, and allowed to remain 

 empty and dry till the end of October. 



The catchment basin of this branch of the Owenea is 

 composed of metamorphic rocks, mostly mica-schists 

 containing occasional thin beds of crystalhne limestone, 

 quartzites, and altered basic intrusives (epidiorites). The 

 limestone is not present in sufiicient quantity to have much 

 effect on the character of the water. The valley is 

 cultivated, but the higher ground, where a number of lakes 



