REPORT OF THE COMMISSIONER OF FISHERIES IX 



oyster and of the factors affectino; spawninfi;. Additional evidence 

 Avas secui-ed which indicates that hydro<ren sulphide (H.S) <renerated 

 by a deposit at tlie bottom of the l.ay was an important factor in 

 cansinii- the death of yonnij- oysters. Valuabh^ data bearing on the 

 larval history and the etfeets of temperature on spuwninij; were also 

 obtained. At Milford, Conn., dnrino; the summer of li)2;5, the work 

 of testing- the elfect of materials occurrin<^ as polhitants. and ex- 

 periments in a new method of artificial oyster propagation, were 

 carried on. Encouraging results Avere obtained in the experiments 

 with artificial propagation, and it is hoped that in time the methods 

 devised may be develo])ed to a stage Avhere they may be made an 

 important adjunct to commercial oyster culture. It is of interest 

 that the oysters artificially propagated during the season of 1923 

 and placed in the harbor survived the winter and attained con- 

 siderable growth. An account of these experiments has been pub- 

 lished as Bureau of Fisheries Document No. 9G1, for tlie benefit of 

 practical oyster groAvers and biologists. The Avork Avill be con- 

 tinued during the coming fiscal year. 



FRESH-AVATER MUSSELS 



Fresh-Avater mussels form the basis for the most important fishery 

 in the Mississippi drainage. In 1922 the take of shells alone 

 amounted to nearly 52,000,000 pounds, Avith a value to the fishermen 

 in excess of $1,000,000. The manufactured products, including pearl 

 buttons, poultry grit, lime, etc., had a value of about $7,000,000. 



The investigation of the fresh- Avater mussels of the Mississippi 

 Valley has been carried on as usual from the Fairport (loAva) 

 biological station. Mussel surAeys Avere made in Lake Pepin, on the 

 Mississippi RiA^er betAA-een Dubuque and Keokuk, loAva, and in Ar- 

 kansas on the White, Black, and St. Fi-ancis Kivei's. The Lake Pepin 

 survey Avas one of a series of annual surveys that are being made in 

 order to determine the effect of the propagation of the fat mucket 

 {Lampf^Uis Ivteola) and the alternate closure, for four-year periods, 

 of various sections of the lake, and the results thus far attained are 

 most promising. In Arkansas the survey Avas made for the purpose 

 of assisting that State in establishing areas that should lie closed for 

 a period of years in order to restore the depleted nmssel betls. 



The experiment, started during the previous fiscal year, in the 

 rearing of mussels in troughs through their early life did not prove 

 as successful as Avas anticipated. It is believed that this method for 

 projiagating mussels Avill prove to be of great importance if it can be 

 perfected, and special attention is being given to this Avork. 



A special iuAestigation of the parasitic stage of the nmssel was 

 continued l»y Dr. L. B. Aiey. of XortliAvestern University. Attention 

 was giAen to a study of the normal cyst and the relationship existing 

 between the mussel embryo and the host fish. The innnunity to re- 

 peated inoculations developed by the host fish Avas also stiulied. 



The adult mussels retained at the Fairport biological station have 

 been found to be infected Avith a ciliate parasite, Avhich invades the 

 brood ])ouches and destroys numbers of young larval mussels 

 (glochidia) before they are liberated by the parent. It is believed 

 that this condition is dependent upon a polluted condition of the 



