186 



Part III. — Twenty -second Annual Report 



6. Witch (Pleuronectes cynoglossus, L.). 



There now exists a considerable amount of material to show the growth 

 of this flat-fish in the earlier period of its life, for the first few generations, 

 young forms having been procured in the tow-nets or the fine-meshed net 

 used with the otter-trawl. 



The witch spawns rather later than most of the other pleuronectids. 

 On the east coast of Scotland the spawning period was found by me to 

 extend from May to August, the maximum spawning occuring about the end 

 of June.* Cunningham found it spawning in the Clyde towards the end 

 of June,f and Williamson obtained the floating eggs in Lochfyne in each 

 month from April to August inclusive — sparingly in these two months, 

 and most abundantly in June. % Holt found ripe specimens on the west 

 coast of ^Ireland in March, April, and May, and expressed the opinion that 

 it also spawns in June; § and Herdman and Dawson, with reference to the 

 Irish Sea, describe this fish as spawning from May to July.il 



The spawning period may therefore be regarded as extending from April 

 into August, with a maximum towards the end of June. 



The egg measures from 1*15 to l"19mm. and according to Cunningham 

 hatches at temperatures varying from 53° to 68° on the sixth day, and 

 at lower temperatures on the ninth day. Holt found that the eggs 

 fertilised by him on 14th May hatched mostly on the seventh day; 

 some as early as the sixth and others as late as the ninth day, but the 

 temperature of the water was not noted. The surface and bottom 

 temperatures off the Firth of Forth, where the depth is about thirty 

 fathoms, are approximately as follows in the months during which the 

 witch spawns. 





April. 



May. 



J une. 



July. 



August. 



Surface, - 



43-3° 



46-5° 



51° 



54-3° 



55° 



Bottom, - 



41-6° 



44-3° 



45° 



48-5° 



51-5° 



The lower temperatures mentioned by Cunningham are not specified, 

 and the eggs of the witch were not among those submitted to temperature- 

 experiments by Dannevig at Dunbar. But in the experiments referred 

 to % it was found that the egg of the cod, w r hich is larger than that of 

 the witch, being about l^mm., took 15| days to hatch at a temperature 

 of 42^8, 12| days at 46°'4, 10J days at 50°, and 9f days at 53°'6; 

 while the egg of the flounder, which is smaller than that of the witch, 

 measuring 0'95 to l-05mm. in diameter, at the same temperatures hatched 

 in 6J, 5|, 4| and 3f days respectively. It may therefore be assumed 

 that if the bulk of the eggs of the witch be spawned in the latter part of 

 June, the majority of the larvse hatch out about a week later, or, approxi- 

 mately, at the beginning of July. The hatching period, owing to the 

 influence of temperature, will be more contracted than the period of 

 spawning. 



* Eighth Ann. Report Fishery Board for Scotland, Part TIL. p. 263 (1890) ; Ninth ibid. 

 p. 264 ; Tenth ibid., pp. 234, 242. 



f Trans. Roy. Soc. Edinr., vol. xxxii., Pt. I., p. 101 (1887). 



X Seventeenth Ann. Rejp. Fishery Board for Scotland, Part III., p. 99 (1899). 



§Rep. to Council, Roy. Dublin Soc. for 1851, p. 258 (1892). 



|| " Fishes and Fisheries of the Irish Sea," p. 55. (1902). 



II Thirteenth Ann. Rep. Fishery Board for Scotland, Part III., p. 147. 



