commercial shellfisli. The methods of ai)i)hcati()U 

 proposed by these authors, however, were de- 

 signed to restrict the dispersal of the pesticide. 

 Com])ounds relatively insoluble in water were 

 dissolved in polychlorinated benzenes, whith are 

 tliemselves virtuallj- insoluble in water — a charac- 

 teristic that further limited the solubility of the 

 |)esticide. \Ioreover, the polychlorinated benzenes, 

 which are heavier than sea water, were mixed 

 with dry sand to anchor the pesticide to the 

 bottom of tlie ])articular shellfish bed treated. 

 This essentialh' two-dimensional treatment of 

 limited areas with a control pesticide had little or 

 no effect on jjelagic or planktonic organisms. 



Butler, Wilson, and Rick (1962) ])resented data 

 on the effects of some j)esticides on adult oysters 

 and Davis (1960) reported the effects of 31 com- 

 ])ounds, including several tyi)es of pesticides, on 

 fertilized eggs and larvae of bivalves. The authors 

 of the two pajiers considered the effect of pesti- 

 cides on growth to be the most sensitive index for 

 these moUusks. 



The highest concentration of any pesticide that 

 can be considered "safe" for use in waters in 

 which valuable species of bivalves reproduce is 

 the highest concentration that has no appreciable 

 effect on survival of the developing embryo or on 

 growth and survival of the fully formed veliger 

 larvae. It is also necessary to determine the con- 

 centrations tolerated by spawning individuals and 

 by organisms that serve as food for larval and 

 adidt bivalves (Ukeles, 1962). 



A distinction is made between effects on devel- 

 opment of the embryo and on siu'vival and growth 

 during the larval stage because tolerances of these 

 two pelagic stages to a given toxicant are often 

 markedly different. Growth of the veliger larvae, 

 moreover, may be drastically retarded at con- 

 centrations of toxicants too low to cause direct 

 mortality of either embryonic or larval stages. 

 Such a retardation of growth, however, serves to 

 prolong the pelagic life of the larvae and, thus, 

 increases the chance for their loss through preda- 

 tion, disease, and dispersion. 



This report summarizes the data obtained at 

 the Bureau of Commercial Fisheries Biological 

 Laboratory in Milfoi-d concerning the effects of 

 various compounds used in control of various 

 types of undesirable organisms, on the develop- 

 ment of fertilized eggs of hard clams, Mercenaria 

 mercenaria, and American oysters, Crassostrea 



virgiiiica, and on the survival and growth of the 

 larvae. The data, unfortunately, are not complete 

 for all of the compoimds tested. The work on 

 pesticides at the laboratory in Milford has been 

 terminated by transfer of pesticide work to the 

 Bureau's Biological Laboratory at Gulf Breeze, 

 Fla. In the early experiments the efl'ects of the 

 compounds on development of fertilized eggs were 

 not tlctermined and many were tested in onlj' a 

 single experiment. Fintliermore, for some experi- 

 ments in which growth of larvae in control cid- 

 tures was not satisfactory, we can give only the 

 data on development of fertilized eggs. The effects 

 of a number of these pesticides on some of the 

 algal foods of bivalve larvae liave also been 

 determined (Ukeles, 1962). 



METHODS 



Methods for spawning oysters out of season 

 and standard methods for cidturing the larvae 

 have been described in detail by Loosanoft" and 

 Davis (1963). These methods were followed 

 throughout the present series of experiments. 



Li most experiments all pesticides were tested at 

 concentrations of 0.25, 0.50, 1, 2.5, 5, and 10 p.]).m. 

 (parts i)er million), with duplicate cultures at each 

 concentration. If a toxic range was not established 

 in the first experiment, these concentrations were 

 increased or decreased by a factor of 10 in the next 

 exi)erimeut. Usually, however, the range of 0.25 

 to 10 p.jj.m. included concentrations that had no 

 eft'ect and concentrations that caused 100 percent 

 mortality. .Stock solutions of water-soluble pesti- 

 cides were made up in water; all otfiers were made 

 ui) in acetone, except for a verj- few that were in- 

 solul)le in either water or acetone. The latter were 

 used as water suspensions. 



For observations on development of eml)ryos, 

 fertilized eggs were introduced into the test con- 

 centrations soon after release and fertilization, 

 usually when the eggs were in the two-cell stage of 

 develojjment. Quantitative samples were taken 48 

 hours later to determine the percentage of the 

 fertilized eggs in each cidtui-e that had developed 

 to noimal straight-hinge veliger larvae. 



For tests to determine the effect of compounds 

 on survival and growth of veliger larvae, we used 

 cultin-es of 2-day-old larvae that had been reared 

 to the straight-hinge stage under normal conditions. 

 These larvae were then reared, in the different 

 concentrations of substances being tested, for a 



394 



U.S. FISH AXD WILDLIFE SERVICE 



