RAPPORTS. XIII C4: MASTERMAN — l8 — 



He suggests that, as on one and the same ground, plaice may be found feeding on 

 Mollusca and dabs on Crustacea^ it would appear that plaice have the better organs 

 of touch, and dabs of sight. He therefore holds that the diet depends first on the or- 

 ganisation of the plaice, second, on the food grounds, and third, on the physiological 

 condition of the plaice for the time being i. e. when hungry it would eat anything, whilst 

 when nearly satiated it would specialise and he suggests that hunger is the cause of the 

 fish swallowing sand grains and shell fragments. 



The main conclusions arrived at in the foregoing (Food and Foodgrounds) seem 

 to be. — 



Plaice would appear to find their food by touch, dabs by means of sight, and that 

 the fact that plaice eat more Mollusca and Polychaeta and dabs more Crustacea (this 

 species is practically omnivorous) is accounted for by this supposition. 



Todd remarks on this "I would suggest, however, even if this is the case in the 

 older fish, that it is not so in the first bottom stages, but that the plaice then finds its 

 food by sight — consisting as it does, mainly of active Crustacea. 



"My own theory is certainly in favour of feeding by sight. I cannot otherwise imagine 

 how a plaice could eat siphons of Solen (which I have frequently found in stomachs) if it 

 fed by touch, mere contact with a Solen siphon causing it to retract rapidly, probably 

 too rapidly to admit of its being bitten off by the plaice. In fact, a Solen requires rather 

 careful "stalking". Hefford informs me also that plaice in aquaria certainly feed by sight. 



"The supposition that the presence of sand and shell fragments is due to hunger is 

 I am inclined to think incorrect. I have always supposed them to be taken in with other 

 food, and that the fish has not troubled to disgorge them, but this of course may in itself 

 be due to hunger — the fish being in too much of a hurry to feed, to trouble about 

 extraneous matter. I should, however, say that plaice only eat sand and shell-fragments 

 either in conjunction with food or in abortive attempts at capture". 



Food and time of day — Franz also finds differences in food at different per- 

 iods of the day (morn or even) — he finds from two series (Helgoland and Lorelei Bank) 

 that in the day plaice eat more Mollusca, in the night more Amphiura. 



Amphiura seems to be an exception to the accepted generalisation that the plaice 

 is a day-feeder. This invertebrate is phosphorescent on contact and ■ therefore would be 

 more conspicuous at night. As the food shows a daily period the plaice must get rid 

 of indigestible remains within 24 hours. 



These observations seem important as if the food takes 24 hours to pass out, then 

 the contents of the stomach and intestines constitute a day's supply. 



Food and time of year — The results as far as they go corroborate those of 

 Todd — that plaice do not feed much in the winter (November to February). 



Food migrations (?) — In this connection he disagrees with Heincke in supposing 

 that plaice migrate in search of food, Heincke's theory being that most of the bottom 

 animals are annual and therefore reach their maximum development at a fixed time of 

 the year. The food species are shown to be mostly perennial and one can always find 

 several year-groups, therefore it is obvious that if an animal occurs on a certain ground, 

 it occurs throughout the year in various stages of development. It follows that feeding 

 grounds must be equally profitable at all times of the year and fish would not need 



