72 PRELIMINARY EXPERIMENTS ON 



According to Professor Ewart,* Danuevig also set free a number of 

 young herring in the same pond. Some completed their metamorphosis, 

 but the greater number fell victims to the hungry cod. 



Lastly, in 1896, Mr. Harald Dannevig,t at the Dunbar hatchery, 

 succeeded in rearing a number of plaice through their complete meta- 

 morphosis, in a glass carboy holding ten gallons of sea-water. Twelve 

 hundred larvre were introduced, but the proportion of the survivors is 

 not stated, except that the healthy larvae, from which alone the survivors 

 were derived, formed the minority from the beginning. The water was 

 changed once or twice a day, and plankton from the harbour was added 

 twice a day. The water in the carboy was subject to convection 

 currents, caused by inequalities in the temperature of the water and 

 that of the surrounding air. To the gentle movements of the water, 

 due to this cause, Mr. Dannevig attaches much importance. The oldest 

 stage described by Dannevig is that of an average specimen of the 

 forty-fifth day, which had been on the bottom of the jar for several 

 days, and measured 13-76 mm. (jV inch) in length, and 6-4 mm. (I inch) 

 in breadth. 



On the other hand, the difficulties of the problem are clearly brought 

 out in the numerous unsuccessful experiments described by Cunning- 

 ham,! s-^d by MM. Fabre-Domergue and Bietrix,§ as well as by the 

 experiments known to have been made without result by other 

 naturalists. Cunningham's experiments dealt chiefly with pelagic eggs ; 

 those of the French naturalists were based upon the demersal eggs of 

 Coitus, but also included experiments with various kinds of pelagic 

 eggs. 



When the metamorphosis of a Teleostean larva has been accom- 

 plished, however, no further difficulty in rearing the young fish is 

 experienced in most cases. This remark is particularly true of bottom 

 fishes, such as flat fishes and gadoids, which have been repeatedly reared 

 from the earliest adolescent stages even up to maturity, both in the 

 Plymouth Laboratory and elsewhere; and it has been shown that the 

 rate of growth is principally dependent upon the temperature and the 

 food-supply to which the young fishes are subjected — conditions which 

 can easily be controlled. There can, indeed, be no doubt that the 

 possibilities of marine fish culture would be great and various, if we 



" On tlie Artificial Hatcliing and Rearing of Sea Fish." Fifth Report Scottish Fishery 

 Board, 1886, p. 235. 



t "Ou the Rearing of tlie Larval and Post-larval Stages of the Plaice and other Flat 

 Fishes," loc. cit., pi). 175-192 ; also Sixteenth Report, pp. 223-4. 



X " Experiments on the Rearing of Fish Larvre in 1894." Journal of the Marine Biol. 

 Assoc, iii., 1894, p. 206. 



§ "Recherches biologiques applicables ii la Pisciculture Maritime." Ann. Sci. Nat. 

 (viii.), t. 4, 1897, pp. 151-220. 



