ZOOLOGICAL SOCIETY BULLETIN 



1083 





,(■;■■•?,•/■. 



l)l)(i SALMON SCAI.K 

 Mature Male 31 % inclies long, f'ourtli \e;\r. 

 (Copied from U. S. Bureau Fisheries BidU-tin.) 



points out, irregularities occur, due to other 

 causes than purely seasonal ones, and consid- 

 erable experience is necessary for the correct 

 interpretation of many cases, while a small 

 number of doubtful scales have been found. 

 These latter are too few, however, to affect the 

 general results, and further study may entirely 

 eliminate them. 



The five species of Pacific salmon: Sockeye 

 or Red Salmon {Oncorhynchtis nerka), King 

 or Chinook Salmon (0. Tschawytscha) , .Silver 

 or Colio Salmon (0. kisuich), Dog Salmon [O. 

 keta) and Humpback Salmon (O. gurbiiscJia), 

 were all investigated. 



Reference to the following summary of re- 

 sults will show interesting differences in the 

 spawning age and habits and the time of the 

 seaward migration of the young of the various 

 species of this genus. The humpback, for ex- 

 ample, is much less plastic than other species, 

 spawning always at a definite age and running 

 to sea as soon as hatched, while the chinook fe- 

 males may spawn in the fourtii to the seventh 

 year and go seaward either as fry or yearlings, 

 while a few males develop precociously and 

 never enter the salt water. As they all die 

 after spawning, the same differences in length 

 of life naturallv obtain. 



Siimmari/ of Gilbert's Results. 



The sockeye spawns normalh' either in the 

 fourtli or fifth year, the females being prepon- 

 deratingly four-year-old fish. The young mi- 

 grate seaward shortly after hatching or may 

 remain in fresh water until the second spring. 



Chinook salmon spawn normally in the 

 fourth, fiftii, sixth or seventh year, but four- 

 year-old females preponderate. The young mi- 

 grate soon after hatching or remain in fresh 

 water till the second spring. 



Silver salmon spawn normally only in the 

 liird j-ear. The young migrate either as fry 

 or 3'earlings, but adults are developed almost 

 exclusively from the latter. 



Dog salmon mature normally in the third, 

 fourth or fifth year and pass to sea as soon as 

 they are able to swim. 



Humpback salmon mature always in their 

 second year and migrate to the sea as soon as 

 they are free swimming. 



Pacific salmon "grilse" are precociously de- 

 veloped and conspicuously undersized fish 

 which sparingly accompany the spawning run. 

 So far as known they are male only in the chi- 

 nook, silver and dog salmons, and usually so 

 in the sockeye, except in the Columbia River, 

 where the two sexes are about equallj' repre- 

 sented. Grilse of the silver and dog salmon 

 are in the second year, of the chinook in the 

 second and third, and in the sockeye in the 

 third year. 



The great differences in size of the individ- 

 uals in a run are closely connected with age, 

 the younger fish always averaging smaller than 

 those a year older, thougli the size curves over- 

 lap somewhat. R. C. O. 



THE HALF-MOON FISH. 



LOCAL fish fanciers have in the past few 

 months been greatly interested not to 

 say excited, over the introduction of a 

 strikingly handsome little fish su-table for small 

 aquaria. This is the half-moon fisli (Pterophyl- 

 litm scalare, Cuvier & Valenciennes), called also 

 butterfly fish by the fish fanciers, although it 

 lias no relation whatever to the butterfly fishes 

 of the tropical seas. 



The species has been known for some time 

 to German aquarists, but has only recently been 



