BULLETIN OF THE UNITED STATES FISH COMMISSION. 113 
Vol. VII, Vo. 8. Washington, D. C. Oct. 12, 1887. 
3S. — HATCHING COD IHT NORWAY.* 
By CARL ROGNERUD. 
[Report of the codfish hatchery at Flodevig, Norway, for the year 1886.] 
The unusual low temperature of the sea- water has this year put sev- 
eral new obstacles in the way of the work, so that the results, although 
better than those of preceding years, have not come up to what might 
have been expected, when we take into consideration the advantages 
of the accumulated experience of many years. 
The greatest obstacle to the work was caused by the ice, which pre- 
vented parent fish from being obtained at the most important time, 
namely, from the 26th of February to the 30th of March. After that 
date it is always very uncertain and difficult to get fish which are not 
either too far advanced in spawning or have not already spawned. 
When, nevertheless, a larger number of eggs was incubated than in 
previous years, it must be ascribed to the method of keeping the parent 
fish swimming in a special place in the hatching-house, instead of, as 
formerly, in an open vessel by the wharf. 
In further explanation I may say that already in 1884 I noticed that 
a very large portion of the roe we received was dead when taken from 
the fish, and consequently useless for incubation to such an extent that 
three-quarters had to be discarded. It became of the greatest neces- 
sity to find out the reason for such a great loss and how it could be 
prevented or at least minimized. To assist me in this matter I applied 
for information to several persons of experience, but even with their as- 
sistance the problem could not be satisfactorily solved. The only way 
open to me was to proceed with the necessary investigation myself, and 
after a long time my labor was at last crowned with success. 
The specific gravity of the roe is the surest sign of its being dead or 
alive. When alive, it floats easily in water with a specific gravity of 
1.024; whereas if dead, it sinks and lies on the bottom, even when the 
specific weight of the water is increased by the addition of salt solution 
to 1.030. This fact is taken advantage of to remove the dead and use- 
less roe when the apparatus is cleaned. When the roe is taken from 
the fish, fecundated, washed, and put in a large glass cylinder with 
water of a specific gravity of 1.022 to 1.024, a difference will at once be 
noticed between the good and useless. The living roe will after a few 
minutes float up to the under part of the surface, and the dead sink to 
the bottom, leaving a space of clear water between the two. 
* Translated from the Norwegian by N. Ohman, 
Bull, U. S F, 0. 87' — -8 
