262 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



house with the pipes supplying the filtering boxes, and another is led into the lower 

 part of the shoot for the waterwheel. By means of the eocks, the supply of water for 

 both these purposes can be easily regulated. 



Since each of the sixteen hatching boxes requires between 00 and 100 gallons of 

 water per hour, and the waterwheel about 800 gallons; and since each inch of depth 

 in the pond is equivalent to about 480 gallons, the utilization of the water in this 

 manner from 1L o'clock at night to about in the morning will reduce the level of 

 the water in the pond to the extent of only about 2.1 to 3 feet. This cau soon be made 

 up when the pumps are put on. The fish at present used — plaice — do not require a 

 constant circulation to be maintained; indeed, in some preliminary operations in the 

 tidal pond it was found that eighty large flatfish (including a few common soles) could 

 be kept for two days and three nights in about 7,000 gallons of water, in perfect health, 

 without the water being renewed or any circulation maintained. It would be proba- 

 bly different with more actively-breathing fish, such as cod. 



Another advantage of retaining the water in the spawning pond during night is 

 that the impregnation of all the eggs is made more certain and with a relatively 

 smaller number of males than would be the case were a constant overflow kept up. 

 Spawning takes place at night and the eggs are confined floating iu the pond for 

 many hours. In the morning the pumps are started, and a very gentle circulation 

 maintained during the day; in the afternoon a large volume of water is poured in, 

 and in the course of a few hours practically all the eggs in the pond are collected in 

 the spawn-collector. 



The number of plaice at present in the spawning pond is 220, ranging in length 

 from 14 to 27 inches; but they are being added to, it being estimated that the pond 

 can accommodate more than double the number named. There are two males to three 

 females, this being the proportion of the sexes which obtains in the sea;* but it is 

 probable that the proportion of females may be considerably increased (and therefore 

 the functional capacity of the pond), owing to the special facilities for impregnation 

 adverted to above. 



The hatchery has been in operation only for a few weeks, and, so far, with the 

 greatest success. The death rate among the eggs has been exceedingly small, far 

 below what is usual with cod eggs. Mr. Harold Dannevig has charge of the hatching 

 operations, and to his systematic attention much of the success is due. It is hoped, 

 later in the season, to proceed with the hatching of the common sole, lemon sole, and 

 possibly the turbot; and it should be stated that the present plant — boiler, pumps, 

 ponds, waterwheel, etc. — is sufficient for a hatchery double the size of the one exist- 

 ing, i. e., for between 30 and 40 of Dannevig's apparatus. 



* Vide a paper by the writer on The Reproduction, Maturity, and Sexual Relations of the Food 

 Fishes: Tenth Annual Report Fishery Board lor Scotland, part III, p. 239. 1892. 



