pH, and dissolved oxygen were measured 3 times a week. Ammonia, nitrates, 

 reactive phosphorus, pH, alkalinity, salinity, and dissolved oxygen were 

 measured weekly in the waste treatment reservoir. Water temp was measured 

 daily. Eight groups of clams were used, each receiving a different diet. 

 Initial number of clams in each group was 250,000. This was reduced as the 

 experiments progressed, but each tank contained the same numbers. A 9th 

 control group was held in raw flowing seawater and given no additional food. 

 Shell height was the index of growth. The experiment showed that it is 

 possible to culture hard clam in a recirculating seawater system. A diet of 

 Phaeodactylum tricornutum alone is not sufficient. Diets of Platymonas sp. 

 with P. tricornutum and Rhodomonas sp. , or with Isochrysis galbana substituted 

 for Rhodomonas , gave fastest growth. A diet of Phaeodactylum and Rhodomonas 

 gave poorest growth. Other mixtures gave intermediate growth. Growth in all 

 groups, except that fed Phaeodactylum only, showed a sharp upward inflection 

 after 13 weeks. Either this pattern is characteristic of M. mercenaria or 

 none of the diets was good for newly metamorphosed clams but several were 

 good for larger stages. The fastest growing group had a mean shell height 

 of 0.46 cm after 22 weeks. If growth were linear from time of metamorphosis 

 clams would be 1.09 cm in a year. This would be faster than under natural 

 conditions. - J.L.M. 



790 



Haskin, Harold H. 1950. 



Growth studies on the quahaug, Venus mercenaria. Natl. Shellf. Assn., 

 Convention Addresses 1949: 67-75. 



Length, height, thickness, volume, and weight of all sizes available were 

 measured. When height, width, or cube root of weight is plotted against 

 length the relationship is a straight line. Thus, there is no change in 

 proportions with growth. If the relationship is plotted from averages of 

 groups of 10 clams, one variable can be estimated from the other with an 

 error of less than 5%. On this basis it was decided to use weights. Clams 

 ranging in size from 10,000/bu to less than 200/bu were planted at Cape May. 

 Weight increments for the 1947 growing season were measured. The smallest 

 showed greatest gain: 570% weight increment; the largest increased only 7%. 

 At this location 1 bu of seed clams weighing about 1/3 oz each would yield 

 18 bu medium-sized clams in 5 growing seasons. Relative growth in the same 

 area in 1948 and in 4 other areas in 1948 was less than in the 1947 

 experiment. One-oz seed planted under conditions existing at Cape May in 

 1947 would grow to chowder size in 3 to 5 yrs. Under 1948 conditions 7 yrs 

 would be needed. Some exchange between the clam and its environment, limited 

 by surface area of clam, controls season's growth. As the clam grows, the 

 ratio surface area/volume becomes unfavorable and growth slows. At a certain 

 stage the clam reaches a size at which it will grow only in favorable growing 

 yrs. For Cape May in 1947 that limiting size was 250 g, for Surf City in 1948 

 it was 150 g, for Raritan Bay in 1948 it was 64 g. In Raritan Bay in 1948 

 five size groups were transplanted. The 3 smaller sizes, all below the 

 theoretical limit of 64 g for the area, held their high meat quality. The 2 

 larger sizes, "too big for their new environment" declined sharply in meat 

 quality, to about 2/3 initial level. These studies have shown: 1) the time 

 required for seed to grow to market size, 2) great differences in growth rate 

 for the same year in different localities, 3) growth is limited by surface 

 area, 4) the size limit for a given area will tell a clam farmer whether to 

 grow cherrystones, chowders, or neither, 5) a low theoretical size limit for 

 an area indicates it unsuitable for "laying out" larger clams for any 

 considerable time. Cape shore clams were nearly 2 00 g average weight in 

 7 yrs, Raritan Bay clams only about 75 g at the same age. - J.L.M. 



219 



