404 Part III. — Seventh Annual BepoH 



necessary steam from the engine is also passed into a tank through 

 which the suction pipe travels. 



The average specific gravity of the water in the apparatus was found 

 to be : — 



1884 1 -0*217 \ 



1885 1-0252 I Average for 4 years 



1886 1-023 I 1-023 



1887 1-0247 J 



The maximum specific gravity was 1-027, and the minimum 1-0151, 

 the proportion of favourable to unfavourable days being 3 to 1. 



.During the four years' existence of the hatchery 10H millions of fish 

 fry have been hatched. 



The Rearing of Cod, — Having successfully hatched the ova Mr 

 Dannevig experimented on the vitality of the fry artificially hatched, to 

 see whether these possessed the necessary vital powers for further 

 development in confinement. The fry when liberated are only 6 days 

 old, 3 to 4 mm. in length, and comparatively helpless. To keep these 

 longer and to develop them further, more nourishment must be given 

 to them than is to be found in the filtered water of the hatching 

 apparatus. The first and principal condition for successful rearing is 

 that the water to which the fry is introduced should be of such specific 

 gravity that the fry may, without difficulty, be able to keep clear of the 

 bottom, — the other chief conditions being that the temperature of the 

 water be not too high, that sufficient nourishment be present, and that 

 frequent renewal of the water take place. Accordingly a large basin was 

 built on the shore into which water from a great depth was pumped by 

 a steam engine. Fry of cod, herring and flounders were introduced 

 into this basin in 1886 to the number of half a million, and the rate of 

 growth of cod, as determined, was as follows : — 



Date. 





Age. 



Size in mm. 



April 26 





0 days 



3 



May 3 





6 „ 



5 



„ 16 





10 



7 



„ 18 





21 „ 



8 



„ 21 





24 , 



9 



R1 



? > u ~ 



1 



nion ih 5 



10 



June 3 



1 



8 „ 



12 



it 6 



1 



;, ii „ 



15 



July 12 



2 



» 15 „ 



55 



Aug. 12 

 Sept. 12 



3 



,, 15 „ 



70 



4 



„ 15 „ 



85 



Oct. 12 



5 



» 15 



115 



The greatest rate of increase was between June 6th and July, when the 

 young fish began to eat the food thrown into them several times a day. 



The fish have steadily increased in size. The numbers were greatly 

 reduced, owing to the death-rate being great in the very severe winter of 

 1887-8, the ice in the basin being as much as 20 inches thick. At the 

 end of 2 J years their sizes ranged from 9 to 18 inches. 



Three distinct varieties of cod are distinguished by Mr Dannevig — 

 (1) Light Grey Cod taken in deep water, frequenting a sandy bottom and 

 having white milt and light grey ova ; (2) Red Cod of the shallow alga 

 region round the coast, with yellowish milt and deep orange ova; (3) 

 Darh Grey Cod on grassy bottoms of fjords, with light yellowish grey ova 

 and milt. The larvse in the first stages are of the same colour as the 

 developing eggs. Mr Dannevig holds that the colouring of the cod is 

 inherited and constant and not due to the colour of its surroundings, and 



