435 



Davis, Harry C. 1960. 



Effects of turbidity-producing materials in sea water on eggs and larvae 

 of the clam (Venus (Meraenaria) meraenaria) . Biol. Bull. 118(1): 48-54. 



Eggs and larvae of hard clam were exposed to different concentrations of 

 kaolin, Fuller's earth, chalk, and natural silt. Some eggs developed 

 normally in concentrations of 4 g/1 of clay (kaolin), chalk, or finely 

 ground Fuller's earth, but the percentage developing normally decreased 

 as concentrations increased. In silt concentrations below 0.75 g/1 

 percentage of clam eggs developing normally did not differ from controls, 

 but at higher concentrations percent developing normally was progressively 

 less. No eggs developed normally in silt concentrations of 3 g/1 or higher. 

 Larvae produced by eggs that had developed in high concentrations of each 

 of the suspended materials were reared to metamorphosis after being returned 

 to normal sea water. Larvae were not able to grow in concentrations of clay, 

 chalk, or Fuller's earth as high as those in which eggs developed. Larvae 

 did not grow, and mortality exceeded 90%, at concentrations of chalk above 

 0.25 g/1 and clay and Fuller's earth above 0.5 g/1. Larvae grew normally 

 in silt concentration of 0.75 g/1, and slightly faster than controls at 

 lower concentrations of silt. Growth of larvae was retarded in silt 

 concentrations of 1 to 2 g/1 and was negligible at 3 and 4 g/1. Even at 

 silt concentration of 4 g/1 no appreciable numbers of larvae died within 

 12 days. Larvae were fed daily with a mixture of Isoehrysis and Mono ehry sis . 

 - modified author's summary - J.L.M. 



436 



Davis, Harry C. 1961. 



Effects of some pesticides on eggs and larvae of oysters ( Crassostvea 

 virginiaa) and clams (Venus meraenaria) . Comm. Fish. Rev. 23(12): 8-23. 



Several insecticides, weedicides, oils, organic solvents, antibiotics, 

 bactericides, and disinfectants were applied at different concentrations to 

 hard clam eggs, and larvae. Clam larvae that appear to have been invaded by 

 active pathogens are frequently seen. The bactericides phenol, roccal , and 

 dowicide A and G, soil fumigant nemagon, and fungicide nabam had widely 

 varied effects on clam eggs. Nabam .and dowicide G prevented normal 

 development at each concentration tested. Roccal at 0.1 ppm permitted 

 normal development. At 0.2 ppm it reduced the number of normal larvae by 

 55%, and at 1 ppm and higher it prevented normal egg development. In 

 contrast, dowicide A and nemagon permitted normal development of clam eggs 

 in concentrations up to 5 ppm and phenol was not toxic below 10 ppm. At 

 low concentrations phenol appeared to increase the numbers of eggs 

 developing normally. These compounds were of the same order of toxicity 

 to clam larvae, but showed certain differences. Dowicide G was lethal at 

 all concentrations tested, but nabam did not affect survival of larvae 

 through the 12 days of the experiment at . 5 and 1 ppm, although it almost 

 completely prevented growth. Roccal, dowicide A, and nemagon appeared to 

 be more toxic to larvae than to eggs. Similarly, although normal numbers 

 of eggs developed to straight-hinge stage in 5 ppm dowicide A, all con- 

 centrations of 1 ppm and over were lethal to larvae. Nemagon, even at 10 

 ppm did not seriously affect egg development, but growth and survival of 

 larvae were normal only at 0.25 ppm. Delrad, an algacide, was toxic to 

 clam larvae at concentrations high enough to be an effective algacide. 

 Phenol at 10 ppm had little effect on clam eggs but significantly reduced 

 growth rates of larvae. At lower concentrations, however, phenol and low 

 concentrations of dowicide A and certain concentrations of sulmet, 

 chloramphenicol increased the rate of growth of clam larvae. But even 

 with these compounds, too high a concentration can reduce growth and 

 survival of clam larvae. Sulmet is now used routinely at Milford to prevent 

 growth of harmful bacteria in larval cultures. Phenol, chloramphenicol, and 

 even dowicide A might also be used. Weedicides used all belonged to the 

 methyl urea group. Fenuron and monuron were most soluble and least toxic. 

 In concentrations up to 5 ppm neither affected the percentage of clam eggs 

 reaching straight-hinge. Diuron at 1 ppm significantly reduced the number 

 of eggs developing normally, and at 5 ppm no clam eggs developed to straight- 

 hinge. Neburon, the least soluble, prevented normal development of clam 



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