of the Fishery Board for Scotland. 



225 



VIII.— The POST -LARVAL Stages of the PLAICE, DAB, 

 FLOUNDER, LONG ROUGH DAB, and LEMON DAB. 

 By Harry M. Kyle, M.A., B.Sc, Science Scholar, Gatty Marine 

 Laboratory, University of St. Andrews. (Plates X., XI.) 



During the last ten years an enormous amount of work has been done 

 by scientific investigators* in connection with the life-histories of the 

 important food -fishes, and of these the plaice has received the greatest 

 amount of attention. The life-histories have been approached from two 

 directions. The fertilised eggs have been obtained and kept in tanks 

 until the larvae hatched, and thus the distinctive characteristics of the 

 larval forms made out. The larvse of the plaice is distinguished by its 

 large size when hatched, but the larvse of the other four flat-fishes named 

 are hatched at nearly the same size, the size of the newly hatched larva 

 being related to the amount of yolk contained in the egg. Amid slight 

 differences of description there is common agreement amongst observers 

 that the essential distinctions between these larval forms are to be seen 

 in the distribution and colour of the pigment. If the yolk-sac is still 

 attached, the larvae of the lemon dab can be distinguished from those of 

 the long rough dab, and both from those of the dab and the flounder, by 

 their slightly greater length. But if the yolk is absorbed and pigment is 

 absent, as in spirit specimens, the separation of the young post-larvse is 

 extremely difficult, depending on some minute differences in the con- 

 figuration of the head. Beyond this very early post-larval stage four of 

 these forms have not been traced as yet, but recently the young plaice 

 have been reared through the larval and post-larval stages to the assump- 

 tion of the adult characteristics. 



The other side from which the life-histories of these forms have been 

 approached has been from their pelagic stages and conditions. It has 

 been gradually discovered that in each life-history there is a definite 

 cycle of migration. The long rough dab and lemon dab are deep-water 

 fish, living at depths of twenty fathoms and more, but their eggs and 

 larvse are found within three miles of the shore. The plaice, in its adult 

 mature condition, also frequents deep water, visiting certain spawning 

 areas in the beginning of each year, and from these areas the eggs and 

 larvse drift in towards the shore. Its young stages, during the assump- 

 tion of the adult characteristics, are found in rock-pools and brackish 

 water. The migrations of the dab are not so extensive. It spawns 

 within three miles of the land, although mostly at greater distances. Its 

 larvae and young forms are found within a few hundred yards of the 

 shore. The flounder, again, passes the greater part of its life in fresh 

 water, entering the streams at a very early stage and leaving them only 

 to spawn in the sea. The drifting shorewards of these eggs, larvae, and 

 post-larvae have been connected with the currents which flow southward 

 during the greater part of the year along the coast of Aberdeenshire and 

 Forfarshire into St. Andrews Bay and the Firth of Forth. 



The eggs of four of these forms, the commonest of the pleuronectidae^ 

 along with those of many others, are found together during certain 

 months of the year, especially March, April, and May. The larvae also 

 are found together, and these are separated from the larvae of the round 

 fishes by " the proportionally larger eyes of the round fish, the structure 

 of the tail, and the depression of the snout between the eyes " of the 



* M'Intosh and Prince, "Researches," Trans. R.S.E., Vol. xxxv., Part ii., 1890 ; 

 Trawling Report, 1885 ; and papers in " Reports of Scottish Fishery Board." 



J. T. Cunningham, Trans. R.S.E., Vol. xxxiii., Part i. (1887), and Papers in thft 

 "Journal of the Marine Biological Association." 



E. W. Holt, Sc. Trans, R.S.D., Vols. iv. and v. (Sec. ii.), 1891 and 1893. 



C. G. Petersen, " Report of the Danish Biol. Sta.," 1893. 



T. W. Fulton, "Reports of Scottish Fishery Board." 



