110 MAKKKTAI'.Li: BRITISH MAKIXK FISHES CHAP. 



possible to follow with considerable certainty the history and 

 growth of the fry derived from a certain spawning season, and 

 so discover their condition at successive ages. But in most 

 cases it is found that after the first year the sizes vary so much 

 that the largest one year old cannot be distinguished with 

 certainty from the smallest two years old. Observations on fish 

 of known age in captivity are more certain, and must be instruc- 

 tive, although they are open to the objection that the growth 

 and history may be altered by the unnatural conditions. The 

 flounder however is a fish which bears confinement well, and an 

 experiment was made with a number of these at Plymouth. 

 The young flounders towards the end of their transformation 

 approach the shore and enter bays and estuaries, and in some 

 places are found in April and May in thousands in the pools left 

 by the ebb-tide. Between two hundred and three hundred of 

 these were obtained from Mevagissey in May 1890, and reared 

 in the Plymouth Aquarium. They were i inch long and were 

 about two months old. In April 1891, having been fed regularly 

 but not very liberally, the largest was j\ inches long, the smallest 

 not quite 2 inches. None of these specimens showed any signs 

 of spawning during the season of 1891. The difference in size 

 among them is remarkable enough, but we have good evidence 

 that the same variation occurs under natural conditions in the 

 sea. Plaice in small numbers from if to 3^ inches long are 

 taken in January, February, and March in the Humber, and 

 flounders from 2\ to 4! inches in April. These must have been 

 hatched the previous season, so that it is clear that growth in 

 the sea may be as slow as the slowest in the aquarium, and 

 may also be probably as rapid as the fastest in the latter. The 

 cause of the difference appears to be, first, competition for food, 

 secondly, the dependence of growth on the amount of food taken. 

 If each fish were fed separately the growth would probably be 

 nearly uniform. But where there are a large number, as in the sea 

 or the tank, and a limited supply of food, some get a start, and, 

 having once become a little larger, the more they surpass their 

 companions the better able they are to beat them in the com- 

 petition or search for food. It is reasonable to conclude from 

 these facts that no flounders spawn when one year of age, and 

 the evidence goes to show that the same holds true for other 

 flat-fishes and for sea-fishes generally. 



