EXPERIMENTS ON THE REARING OF SEA-FISH LARV^. 71 



of Kiel. Half the water was changed daily, and was filtered before its 

 introduction into the tub in order to remove all but the most minute 

 organisms from the water. A considerable mortality among the larvae 

 took place after the tenth day, apparently from an insufficient supply of 

 food of the right kind ; but the beneficial effects which followed the 

 subsequent introduction of unfiltered water (containing a richer supply 

 of larger organisms) were so conspicuous that a number of the larvse 

 completed their metamorphosis and were reared to a length of 72 milli- 

 metres (nearly 3 inches), their age at this length being about five 

 months. Unfortunately neither the number nor percentage of the 

 survivors is mentioned. 



Captain Dannevig's* experiment was carried out on a greater scale. 

 He placed about 500,000 young fry of the cod, which had been arti- 

 ficially hatched, into a large basin of sea - water attached to the 

 Flodevigen hatchery on the south coast of Norway. The capacity of 

 the basin was about 2,500 cubic metres (88,000 cubic feet), the greatest 

 dimensions being : — length, 43 metres ; breadth, 20 metres ; depth, 

 5 metres (i.e. about 140 by 66 by 16 feet). During the first month 

 the larvse refused artificial food, and no plankton (minute floating life) 

 was provided for them except such as was already present in the sea- 

 water. They were observed to attack, kill, and eat each other in con- 

 siderable numbers, but were still too small to attack the numerous crab 

 larvse which were also present in the water. From the second month 

 onwards, however, they ate considerable quantities of finely-powdered 

 mackerel, which was given them twice a day, and their rate of growth 

 greatly increased. At the end of the fifth month they had attained 

 an average length of 115 mm. (4^ inches), the largest caught being 

 157 mm. (6 inches) long. At the eighth month the number of sur- 

 vivors was estimated to amount to " several thousands." This famous 

 and most important experiment served Captain Dannevig's purpose in 

 demonstrating that fry artificially hatched have the power to live, grow, 

 and develop when set more or less at liberty ; but it is clear that, 

 strictly speaking, the demonstration is limited to a small percentage! 

 (not more than one or two per cent.) of the original stock of larvae. 

 By the following April, i.e. when about a year old, some of the survivors 

 were about a foot in length. J 



* Report of the Codfish Hatchery at Flodevig, Norway, for 1886. (Translated in Bull. 

 U.S. Fish Covmiission, VII., 1887, pp. 113-19.) 



t Mr. Harald Dannevig, in a reference to his father's experiments, states that " most of 

 the young fishes survived the following winter " {Fifteenth Report Scottish Fishery Board, 

 part iii. p. 176). Although I have not seen the original report, this would appear from the 

 American translation to be a mistake. 



X EwART, Fifth Report Scottish Fishery Board, pp. 235, 244 ; McIntosh, British Food 

 Fishes, p. 244 ; Cunningham, British Marketable Fishes, p. 287. 



