oj the Fisher tj Board for Scotland. 441 



was maintained for another live weeks. This period, during which the 

 greater bulk of the Q^^i^ were produced, was most prolific about the end 

 of the first week in April, and it continued until the 22nd of the same 

 month. By this time, however, the number of eggs decreased rapidly 

 in the pond : most of the fishes had clearly become spent during the 

 heavy production of eggs in April, and the spawning came to a close 

 early in May. As regards the temporary variation in the s{)awning, 

 subsequent to changes in the temperatui-e, several instances may be 

 observed in Table I. Five days aftei- the hatchery was started the 

 spawning ceased altogether for six or seven days. This was caused by a 

 reduction of the temperature of the water in the pond in consequence 

 of a fall of snow. For several days part of the pond was covered with 

 thin boards, supported on large beams, so as to save the surface-water 

 from exposure to the strong and cold winds. A similar fall of tempera- 

 ture occurred at the middle of February, when, in addition to being 

 covered, the water in the pond was artificially heated with waste steam 

 from the boiler. Cold weather with snow set in again at the end of 

 March, but probably owing to the advanced state of the ovarian 

 development the spawning on this occasion was less affected. 



The daily progress of the hatching season will be seen from Table 1. 

 In regard to the specific gravity of the sea-water on the beach a con- 

 siderable variation will be observed. This variation, which is due to 

 the river Dee and in some measure to the fresh ground-water from the 

 surrounding hills, does not usually extend to the deeper layers, from 

 which the supply for the pond is taken. On 14 out of 110 days it was 

 below 27, and on one occasion below 26. Thus the specific gravity 

 of the pond-water was usually higher than the surface-water on the 

 beach, of which a very stiiking instance may be seen from the records 

 for the end of the second week of February. The difficulties previously 

 experienced with water of a low salinity, owing to a leak in the inflow 

 pipe, have thus been remedied, and are not likely to recur again as long 

 as the main supply pipe remains undamaged. Owing to the increased 

 supply of eggs, the storage tank of water for the hatchery was unable to 

 serve the hatching apparatus for the whole night at the most busy part 

 of the season, and an increased death-rate amongst the more advanced 

 eggs was the consequence. During the present year this tank has been 

 heightened considerably, and will be able to serve the present number 

 of hatching appar.itus for about ten hours. 



During the season a total of 65,377,000 eggs were collected from the 

 pond, from which 51,800,000 plaice fry were obtained and planted 

 in the upper area of Loch Fyne. The particulais in connection with 

 the distribution of the fry will be seen from Table II. As in the 

 previous year the ti-ansport was efl'ected at night, and ordinary carboy 

 jars were used. 



[Table. 



