432 



Davis, Harry C. 1953. 



On food and feeding of larvae of the American oyster, C. virgin-Lea. Biol. 

 Bull. 104 (3) : 334-350. 



References to Venus mereenaria are mostly citations of other papers, 

 abstracted elsewhere in this bibliography. However, differences in growth 

 rate of oyster larvae were noted which could not be explained from type or 

 quantity of food available. Variations in physical or chemical constituents 

 of seawater were suspected. An experiment was conducted in which oyster 

 larvae were cultured in laboratory seawater and water brought from Milford 

 Harbor, Conn., in enamel buckets. A single culture of V. mereenaria larvae 

 was started in laboratory seawater at the same time. At 14 days all oyster 

 larvae were dead but Venus larvae grew normally and were healthy, most of 

 them reaching setting size at 18 days. Other experiments showed no 

 difference between oyster larvae grown in laboratory water or water from 

 other sources. It was concluded that the effects on oyster larvae were 

 caused by some widespread water condition to which hard clam larvae were 

 not susceptible. The cause of this "water condition" was not identified. 

 - J.L.M. 



433 



Davis, Harry C. 1954 (? publication date not given). 



On food and feeding of larvae of the American oyster, C. virginioa. Proc. 

 Natl. Shellf. Assn. for 1952: 54-69. 



Poor growth and high mortality in some experiments may have been caused by 

 variations in water quality. An experiment was designed to compare 

 laboratory seawater with water from Milford Harbor. Parallel cultures of 

 oyster larvae were started, 2 in each type of water. A single culture of 

 Venus mereenaria larvae also was set up in laboratory seawater. All 

 cultures received about 50,000 cells/ml/day of mixed Chlorella for food. 

 At 14 days all oyster larvae in both types were dead. Venus larvae 

 appeared healthy and were growing normally, although growth was slower 

 than average. At 18 days Venus larvae were at setting size and 55% of the 

 straight-hinge larvae had survived. - J.L.M. 



434 



Davis, Harry C. 1958. 



Survival and growth of clam and oyster larvae at different salinities. 

 Biol. Bull. 114(3): 296-307. 



Eggs of hard clam from Long Island Sound can develop into normal straight- 

 hinge larvae only within the salinity range 20 to 32.5°/oo. At 35°/°° only 

 1% or less of eggs developed into shelled larvae, and at 17.5°/°o none. 

 Even at 20°/°° only 16 to 21% of eggs reached this stage, and at 32.5°/°° 

 only 34 to 52% reached shelled stage. Thus, optimum salinity for eggs was 

 about 26.5 to 27.5°/oo. Growth of clam larvae was comparatively good at 

 salinities 20°/°° and higher, up to 27°/oo. Rate of growth of larvae 

 decreased at each successively lower salinity. At 17.5°/oo some larvae 

 reached metamorphosis, but growth was slower than at 20°/°° and above. At 

 15° /oo larvae grew poorly, were sluggish and susceptible to attack by 

 protozoa, fungus, and bacteria. At 15°/°° 95% were dead by 12th day and all 

 died before setting. At 12.5°/°° a few hard clam larvae survived beyond 

 8th day, but mortality was 95% by this time. Rather than growing, these 

 larvae decreased in size, and shells apparently were disintegrating. At 

 10°/°° or less larvae did not grow, and all died within 6 days. Lower 

 borderline salinity for hard clam larvae appears to be about 17.5°/°° but 

 clams probably are vulnerable to other environmental variables at these 

 low salinities. Embryonic stages of hard clam can not tolerate as wide a 

 range of salinity as can larvae. - J.L.M. 



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