16 



Part III. — Twenty -eighth Annual Report 



TIL — EXPERIMENT IN RETARDING THE DEVELOPMENT OF 

 THE EGGS OF THE HERRING. By H. Chas. Williamson, 

 M.A., D.Sc, F.R.S.E., Marine Laboratory, Aberdeen. 



In the spring of 1908 I carried out some experiments on the retardation 

 of the eggs of the herring.* A certain amount of success was achieved in 

 prolonging the period of incubation to 50 days. At the request of the 

 Government of New Zealand, the experiment has been continued this spring, 

 unfortunately without success. 



On the previous occasion the difficulties which were specially met with 

 were:— (1) To cool the water and keep it at a steady temperature; (2) to 

 aerate the eggs properly. 



This year these difficulties remained to be solved. The cooling of the 

 water was successfully attained by means of a series of iron pipes which 

 were covered with ice. A much more even temperature was in this way 

 obtained. The quantity of water which was lowered to the desired tempera- 

 ture was small, and averaged about one pint in a minute. 



The second problem of the aeration of the eggs seemed to be solved by 

 the adoption of a mechanical system, which is shown in the accompanying 

 sketch, viz., Incubating tank. (Plate I.) 



The apparatus consisted of a galvanised sbeet-steel box T, measuring 35 

 inches in length, 16 inches in breadth, and 15 inches in depth. Inside this 

 tank there were two revolving frames, A and B. Four glass plates bearing 

 herring eggs were fixed on the outside surfaces of A, while five plates were 

 set in grooves inside B. The frames revolved in consequence of the motion 

 imparted to them by the little water-wheel. The frames were always 

 entirely covered with water. 



Two glass plates stood on edge at the lower end of the tank. The tank 

 contained 30 gallons of water. 



The tank was surrounded with crushed ice. 



The water, already cooled, flowed in on to the surface at one end, and 

 found exit from the bottom of the other end. The quantity of water varied 

 slightly from time to time, as will be seen from the table, p. 17. It averaged 

 one pint in a minute. For a short time during the day the flow was often 

 in3reased to a pint in 30 seconds. The water never ceased running except 

 for a few minutes at a time. 



Air was blown into the water on March 31, and thereafter till the end of 

 the experiment. 



The water-wheel rotated slowly. The frame A required about 6 minutes 

 and the frame B 10 to 15 minutes to make a complete revolution. 



As on the former occasion, the spawn was divided into two portions, part 

 being kept in uncooled water, while the remainder was treated with the 

 cooled water. The temperature of the water is given in the following Tables. 



The temperatures were read by myself and by the attendants. Readings 

 were taken during both day and night. These are given in Centigrade. 

 The range in Fahrenheit is deducedf from the highest and lowest Centigrade 

 readings up till March 21st. From March 22nd onwards a Fahrenheit 

 maximum and minimum thermometer was also employed. It was set during 

 the forenoon usually. The readings given cover, therefore, portions of two 

 days, whereas the Centigrade readings refer to one date. 



The water before being cooled was filtered through sand. 



* " Experiments to show the influence of Cold in Retarding the Development of the 

 Eggs of the Herring {Clupea harengus), etc." Twenty -seventh Report of the Fishery 

 Board for Scotland for 1908. 1910, p. 100. 



t A table of Fahrenheit equivalents to Centigrade readings, drawn up by Dr. T. 

 Scott, was employed for this purpose. 



