BULLETIN OP THE UNITED STATES FISH COMMISSION. 120 



Vol. V, No. 9. Washington, D. C. April 1, 1885. 



94.— THE BATE OF GROWTH OF OYSTERS AT SAINT JEROME'S 



CREEK STATION. 



By JOHN A. RYDER. 



The following notes and illustrations may be of interest as showing 

 the size to which oysters of an approximately known age may grow in 

 a favorable situation within a comparatively short space of time. As 

 already stated in former reports, it is not uncommon for spat to grow 

 to the dimensions of 2 inches across in a single season. 



The accompanying figures represent two specimens of oysters belong- 

 ing to a lot which had attached themselves some time during the months 

 of August and September, 1880, to collectors put down at Saint Je- 

 rome's Creek Station. The spat caught there that season on the slate 

 and other collectors was detached and placed in a caisson to in'otect 

 it from enemies, and left in the creek till 1882, when the writer in July 

 of that year made some drawings of some of the oysters developed and 

 protected as above described. This was approximately twenty-three 

 months, or almost two years since the specimens had existed as free- 

 swimming embryos in the waters of the creek. 



In Figs. 1 and 2; the oysters, reared as above described, are repre- 

 sented. In both, the outline of the spat shell as it appeared at the end 

 of the first year can be distinctly seen. In Fig. 1 this was about 1^ 

 inches across at the end of the first year, when the growth of the shell 

 was almost entirely suspended, but during the next eleven months the 

 shells had been extended about 2 inches more from the hinge end, so 

 that the growth made by the valves in two seasons had aggregated 3£ 

 inches, reckoning from the hinge to the free borders of the valves 

 opposite. 



In Fig. 2 the rate of growth, it will be seen, was not so rapid during 

 the second year, only about an inch more having been added during 

 the second year to the extent of the valves of the spat shell of the first 

 year, so that the rate of growth of the first and second seasons was 

 about equal, the total length of the specimen being 2£ inches. 



Upon opening the specimen shown in Fig. 1, it was found in spawn- 

 ing condition at the time, or about the middle of July, 1882. 



The change from the condition of attachment of the whole under 

 surface of the whole lower or external face of the under valve after the 

 first season's growth is abrupt ; the edges of both valves, as the second 

 year's growth of the shell is extended, are at once turned upwards 

 obliquely to the plane of the surface of attachment, and thus freed, as 

 may be plainly seen when the specimens figured here are viewed from 

 the side. 



Bull. U. S. F. C, 85 9 



