4 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 



Woods Hole, and was continued from June 25 to July 27 on board the 

 steamer Fish HawJc, in Casco Bay, Maine. During August the mate- 

 rial and data gathered were worked over at Woods Hole. At Woods 

 Hole the local fisheries were watched closely in order to determine the 

 advent of spawning schools, and numerous samples of male and female 

 fish were examined in order to secure material for a study of the matur- 

 ing ova and spermatozoa. Two small lots of eggs, aggregating 110,000, 

 were brought to the station and kept under observation during their 

 whole period of development. 



At Casco Bay the season proved peculiarly unfavorable for the 

 investigation, which could not be brought to completion with the lim- 

 ited time and facilities at our disposal. Only a few over 1,000,000 eggs 

 were taken, the first on June 25, the last on July 8. Although this 

 number was sufficient to permit a study of the general history of devel- 

 opment and the preservation of material for a more complete review of 

 the embryology, it proved to be entirely inadequate for purposes of 

 experimentation, which, in order to yield conclusive results and elimi- 

 nate all doubtful factors, requires extensive checks. The impossibility 

 of applying these, and the necessity of limiting the experiments to but 

 one series of those proposed, render this part of the work less valuable 

 than it otherwise might have proved. 



For a discussion of the sources of supply of eggs and the conditions 

 under which they were taken, I refer to the reports of Mr. Locke for 

 Woods Hole, and Lieutenant Swift for operations of the Fish Hawk. 



The results of the investigations may best be considered under 

 the three heads or groups into which they were organized, namely, 

 (1) embryology, (2) surface towings, and (3) experiments. 



1. RESULTS OF EMBRYOLOGICAL STUDIES. 



Under this head will be considered the morphology of the reproduc- 

 tive organs, the general history of development, and observations on 

 the conditions which affect it. In the present connection only a general 

 account showing the similarity in development of the mackerel to other 

 fishes producing similar pelagic eggs (the cod, Spanish mackerel, sea 

 bass, etc.) need be given, prominence being given to only those features 

 which are of most interest to fish-culturists. 



A careful study of the rate of growth of the mackerel leads to the 

 conclusion that maturity is reached at the age of three years, at which 

 time the female is 12 to 14 inches long and the male somewhat smaller. 

 In the region included between Cape Cod and Block Island the spawn- 

 ing season extends from the middle of May to about the 1st of July; 

 but few spawning fish are taken after June 15. At Casco Bay the 

 season probably begins and ends, respectively, about two weeks later, 

 the majority of the fish spawning before the 25th of June. From the 

 time of our arrival a systematic record was kept of the condition of 

 ovaries and testes of as many fish as could be obtained for examina- 

 tion. Very nearly all were partly or entirely spent, and the proportion 

 of fully spent fish increased toward the end of the season, though 



