FOOD OF POST-LARVAL FISH, 435 
stomachs full of diatoms), and in the few exceptional cases of fish which 
are true vegetarians. As examples of these latter cases Herdman (1912) 
shows that post-larval plaice first feed on diatoms before taking animal 
food ; Dannevig (1897 and 1898) also found that the young plaice first 
took diatoms and in some eases Infusoria. The Grey Mullet which is 
herbivorous, with its mouth-parts adapted for browsing, eats in its 
post-larval stage according to Cunningham (1890) chiefly diatoms, 
although A. Scott (1898) has found that the older young eat Copepods 
as well as diatoms. Professor 8. A. Forbes (1882-1884) shows that the 
young Whitefish (Coregonus clupevformis) in a tank with only vegetable 
food nearly all died, whilst they fed eagerly on Entomostraca. Even 
before the yolk is absorbed a pair of small teeth are developed, well 
adapted for seizing animal food such as these small Crustacea (chiefly 
Copepods). Young herring take Mollusk larvee before the yolk is ab- 
sorbed, as do also the pipe-fish, Nerophis lumbriciformis, which hatched 
in a jar in the laboratory. Mollusk larve seem often to be taken very 
early, even before Copepods. 
That a certain amount of selection of food takes place is evident from 
previous records and from our own observations. Dannevig (1897) 
states that only one species at one time was eaten by the baby plaice 
although different individuals might eat different species. It seemed 
as though one individual got used to a certain food and stuck to it for 
a time. Petersen (1894) shows that the Dab, living with the Plaice, 
seleets Copepods of other species from those chosen by the latter fish, 
and Herdman shows that the natural food of fish is often that which is 
not most frequently present, so that the fish must hunt for it. 
The following records show that certain fish undoubtedly prefer 
certain food ; frequently two or three fish will like the same kind. For 
instance, Solea variegata and the few Solea vulgaris examined like the 
same food as the Dab, e.g. chiefly Podon, Temora and Euterpina, so that 
it may well be that the very abundant Dab takes away, in its very young 
stages, the food from its more valuable relatives. It is to be noted, 
however, that whereas Solea eats Crustacea as big as T’emora almost at 
once, the Dab, Pleuronectes limanda, has a period up to about 5mm. 
when no Crustacea are found in its alimentary canal, so that it most 
probably first eats softer food. It is not in the least the case that all 
Pleuronectids eat the same food, for one of the Top-knots, Scophthalmus 
norvegicus, specially eats Pseudocalanus, which is only very rarely found 
in the Soles and Dab, and Arnoglossus although not eating Copepods for 
some time also likes Pseudocalanus. Podon, probably P. intermedius, 1s 
a favourite with many young fish, and is often taken by the very young 
ones before Copepods ; probably it is more easily digested. It heads 
the list of the food of post-larval fish in these records. 
