428 ^'- S. BUREAU OF FISHERIES 



curs duriiiG: the summer and fall months, and is folloAved by rapid 

 reproduction and spore formation in the body of the host. Although 

 the parasite has not yet been identified, its position as a member 

 of the class Sporozoa has been confirmed by Dr. E. R. Kudo of the 

 University of Illinois. 



South Atlantic and Gulf section. — Oyster-pest investigations were 

 undertaken on the Gulf coast, covering the inshore vraters of Florida, 

 Alabama, and Texas. Previous surveys and reports from members 

 of the fishing industry showed that the most destructive pests in 

 this section are the borer, Thais, and the leech, or wafer, Stylochus. 

 Other pests associated with these, but whose relationships as com- 

 mensals or enemies are undetermined, are the boring sponge, Cliona; 

 boring clam, Martesia, and barnacles and mussels. The most serious 

 damage was reported from Apalachicola Bay, Fla., and it was there- 

 fore decided to make this area the headquarters for the Gulf investi- 

 gations. Separate surveys were made in Texas and Alabama. 



Owing to the uncavailability of sea water in Apalachicola, it was 

 finally decided to establish the laboratory at Indian Pass about 20 

 miles away, where electric power could be obtained and communica- 

 tion with Apalachicola was possible by road. The construction of 

 the laboratory was begun on May 20. The site was furnished gratis 

 by its owners, the Lagoon Co., and 'the materials were supplied by 

 the State department of conservation through the cooperation of 

 Commissioner G. W. Davis. By July the building was ready for 

 occupancy. It is of frame construction, consisting of a main labora- 

 tory and six smaller rooms, and a basement for pumps, storage, 

 garage, etc. In August the salt water pump was installed and by 

 September the laboratory was supplied with running sea water. The 

 floating equipment of the laboratory comprises a large and a small 

 skiff, and a cabin cruiser with accommodations for four persons. 



Before the completion of the laboratory, field work was undertaken 

 by R. O. Smith and G. Gunter on the study of the borer problem. 

 Traps of aluminum insect screen, baited with large and small oysters 

 and mussels, were set on oyster bars. This type of trap caught 

 Thais on barren bottoms where no other food was available, but was 

 inefficient where oysters were plentiful. Traps made of copper wire 

 proved toxic to both oysters and mussels used for bait. 



Chicken-wire cages were made to carry out field experiments on 

 the rate of feeding of Thais and destructiveness of this gastropod 

 in various salinities. The cages were placed on 6 different bars 

 with normal salinities ranging from less than 10 to over 30. Un- 

 fortunately freshets brought all salinities down to less than 10 for 

 a long enough period to kill all Thais, the experiment resulting, 

 therefore, only in the proof that oysters can withstand a lower 

 salinity over a longer period than can the borer. 



Laboratory experiments have shown that Thais suddenly subjected 

 to a drop in salinity of from 25 or above to below 10, survive about 

 2 weeks. However, if the change is gradual the borer will live sev- 

 eral weeks without food even though the salinit}^ be reduced to 

 below .5. In any ca^se, both field and laboratory observations show 

 that Thais can live very well m salinities between 15 and 25 parts 

 per mille. 



In contrast to such borers as Urosalpinx and Eupleura^i Thais 

 rarely bores a hole, and has never been found to do so in the thick 



