8 



Part III. — Twenty-second Annual Re-port 



With regard to the influence of temperature upon growth, it is 

 well known from previous observations that fishes, at least in the 

 waters near the shore, grow less quickly in winter than in summer, 

 and may not grow at all if the temperature be very low. In the 

 experiments referred to a number of the food-fishes were kept in 

 tanks in which the water was of different temperature — in one it 

 was considerably above the normal — and the effect on the growth 

 was determined by measuring the fishes after they had been 

 subjected for some time to the various temperatures and comparing 

 the measurement with what it was at first. With a mean tempera- 

 ture of 40 '1 F. it was found that the mean increase in the length 

 of whitings was 1*6 millimetres per ten days, and 2*5 millimetres 

 when the temperature was 48*7 F. ; under the same conditions 

 haddocks grew at the rate of 2*7 and 5*1 millimetres respectively, 

 and codlings increased under the lower temperature at the rate of 

 3 '6 millimetres, and under the higher temperature at the rate of 

 6 "87 millimetres in each ten days. In another tank where the mean 

 temperature was 54'5 F., the rate of growth in length in each ten 

 days was, on the average, 2 '8 millimetres for whitings, 6*45 for 

 codlings, 3'0 for common dabs, and 3'29 for plaice. The growth in 

 length varied generally in relation to the size of the fish as well as 

 to the species, the smaller individuals as a rule growing the quickest, 

 and considerable difference was exhibited in many cases among 

 individuals of the same species approximately equal in size. 



The influence of temperature is exerted directly in connection 

 with the metabolism of the fish, that is, the chemical changes in 

 its tissues, which result in growth as well as in the expenditure of 

 energy. In low temperatures the process of digestion was greatly 

 impaired, and appetite was more or less in abeyance, the fishes 

 refusing their food or eating sparingly. It has been shown that 

 the action of the digestive ferments is suspended at low tempera- 

 tures and increased at high temperatures. The bearing of these 

 observations on the growth of fishes in winter, whether in the sea 

 or in fresh water, is obvious. 



In the same paper the results of the investigations made as to 

 the growth of the Sprat, the Witch Sole, the Norway Pout, and the 

 Sharp-tailed Lumpenus are described, and illustrated by a series of 

 diagrams. 



The Hatching and Eearing of Food-Fishes. 



During the hatching-season of 1903 the number of eggs of the 

 plaice collected from the spawning pond at the Hatchery, Bay of 

 Nigg, was approximately 65,940,000. This was almost the same 

 number as in 1901, and about seven millions less than in the 

 previous year. The number of fry that were hatched from these 

 eggs and retained in the hatching apparatus until approaching the 

 post-larval stage was estimated at about 53,600,000, or a little over 

 81 per cent. The fry were liberated for the most part off Aber- 

 deen, but on three occasions they were taken further north and 

 liberated off Fraserburgh. 



The first eggs were collected on 23rd January and the last on 

 16th May, the period of collection thus extending over 113 days, 

 but the greater number were obtained in March, when 37,080,000 



