NOTE 



DEVELOPMENT OF EGGS AND EMBRYOS 



OF THE SURF CLAM, SPISULA SOLIDISSIMA, 



IN SYNTHETIC SEAWATER 



The eggs of the surf clam, Spisula solidissima, 

 have been used extensively for investigations of 

 egg structure and embryonic development of 

 bivalves. Allen (1951) has pointed out the ad- 

 vantages of the use of surf clam eggs for 

 research of this nature. These studies have been 

 limited, however, to areas where natural sea- 

 water was readily available, due to the unsuit- 

 ability of most synthetic seawaters for support- 

 ing the embryonic development of bivalves 

 (David A. Nelson, NMFS, Milford, Connecticut 

 and Gerald Zaroogian, Environmental Protec- 

 tion Agency Laboratory, West Kingston, Rhode 

 Island, pers. comm.). 



Experimental Observations 



We recently reared Spisi'.lo solidissima em- 

 bryos in a synthetic seawater formulation de- 

 veloped by Zaroogian, Pesch, and Morrison 

 (1969) as a culture medium in which to rear 

 oyster embryos. Our observations were made in 

 salinities of 25 and 30 'Voo at 10°, 15°, and 20°C 

 water temperatures. Within these ranges we 

 found 20°C to be the optimum temperature for 

 development, allowing us to rear eggs to the 

 5-day-old stage (early veliger) with almost 

 100% survival and no signs of larval abnormali- 

 ties. At 20°C polar body formation occurs in 

 about 45 min and the two-cell stage in about 

 90 min. The early veliger, or straight-hinge 

 stage, is reached in less than 24 h. At 15 °C all 

 stages of development are normal but somewhat 

 delayed, with development to the straight- 

 hinge stage requiring more than 24 h. At 10°C 

 the rate of development of all stages is greatly 

 retarded and many abnormal embryos are 

 present. The majority of fertilized eggs held at 

 10 °C requires more than 96 h to develop to the 

 straight-hinge stage. 



At 20° C we found that development of fer- 

 tilized eggs in synthetic seawater was com- 



parable to the best development observed in 

 natural seawater. 



This study did not involve testing embry- 

 onic development of S. fiolidissima in synthetic 

 seawater over a wide range of salinities, but 

 was limited to those salinities currently in use 

 in other research programs within this labora- 

 tory. It appeared that there was no difference in 

 survival and development of eggs to the 5-day- 

 old stage at salinities of 25 and 30 "/oo. the only 

 salinities tested. In earlier work, however, 

 Stickney (in Yancey and Welch, 1968) reported 

 that S. solidissima eggs failed to develop under 

 experimental conditions in salinities of less than 

 23 'Voo in natural seawater. 



Since the synthetic seawater formulation 

 developed by Zaroogian, Pesch, and Morrison 

 (1969) can be readily prepared, its general 

 acceptance could lead to a wider utilization of 

 surf clam eggs by embryologists and cytologists 

 with standardization of techniques and compar- 

 ability of results not always possible when 

 natural seawaters from different locations are 

 used. 



LaRoche, Eisler, and Tarzwell (1970), in 

 studies of bioassay procedures for oil and oil 

 dispersant toxicity evaluation, suggested the use 

 of Zaroogian 's seawater as a standard testing 

 medium in place of natural seawater, the com- 

 position of which varies, especially in regard to 

 the presence of trace metals, dissolved organics, 

 and particulate matter. They recommended the 

 use of Zaroogian 's seawater because of its 

 ability to support spawning adults and larvae 

 of the American oyster, Crassostrea virginica, 

 for at least 48 h without visible adverse effects, 

 and adult mummichog, Fundulus heteroclitus, 

 grass shrimp, Palaemonetes vulgaris, and sand- 

 worm, Nereis virens, for extended periods. 

 Thus, when sufficient research has been per- 

 formed in this area, it may be possible not only 

 to hold adult animals but also to rear the eggs 

 and larvae of these animals in the same syn- 

 thetic seawater. This would be an obvious ad- 

 vantage in assessing comparative tolerances to 

 pollutants of different life stages. 



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