170 



Part III. — Twenty-second Annual Report 



As in all the other tanks, the codlings grew rapidly. In the first hundred 

 days the increments varied from 41mm. to 52mm., the mean being 46*3, 

 and the mean for the ten-day periods was 4-63. In the second the 

 increase ranged from 53 to 54mm., the increments being thus absolutely 

 larger though the period was less and the mean temperature not 

 much higher. The mean increase was 53-7mni., that for the ten-day 

 period being 9*76mm. The total increase in length in the three 

 specimens in the 155 days was respectively, 105mm., 95mm., and 

 100mm., the mean being exactly 100mm., or very close upon 4 inches, 

 and the mean for the ten-day periods was 6-45mm. Of all the fishes, 

 except the flat-fishes, the codlings appeared to be least affected by the 

 changes in the temperature. 



In this tank there were throughout three dabs and one plaice, and 

 another dab was added at the beginning of the second period. They did 

 well, as a rule. In the first period the increments among the dabs 

 ranged from 17mm. to 38mm., the mean increase being 30mm., or a little 

 over 1^ inches, the mean for the ten days being 3'Omm. In the second 

 period the increments varied from 14 to 31mm., the mean increase was 

 17*3mm., and the mean for the ten days, 3 - 15mm. Over the whole 

 period the increments of the dabs in this tank varied from 31 to 56mm. 

 (\\ to 21 inches), the average being 47 -3mm., and that for the ten days, 

 3-05mm. 



Only one plaice was made use of, and it increased in the first period 

 from 226 to 258mm., an increment of 32mm., or a little over 1} inches. 

 In the second period it increased other 19mm., the ten-day mean being 

 3 '45mm., as compared with 3" 2mm. in the first period. The total 

 increase at the end of the experiment was 51mm., giving an average for 

 the ten days of 3 -29mm. 



It may be noted that throughout the whole of the experiment none of 

 the flat-fishes perished, so that they bore the changes in temperature 

 much better than the round fishes. 



An armed-bullhead, or pogge. was also placed in this tank, and 

 survived over the first period, but it did not increase in length at all. 

 Probably like the starry ray this was owing to the food not being quite 

 suitable for it. It died shortly after the beginning of the second period, 

 on one occasion when the temperature rose high. 



These experiments show that the increase in temperature is followed 

 by an increased rate of growth, but I do not think the data are such as to 

 enable the ratio between the two to be determined. In such experiments 

 there are a number of factors which influence the growth, and it is a 

 matter of extreme difficulty to maintain a natural balance among them in 

 the various tanks, and to have the experiments carried on under natural 

 conditions. The influence of the vicissitudes in the temperature at 

 different times of the day or night must be of importance, as shown by 

 the experiments of putting fishes from the cold water into the warm 

 water, the haddock, whiting, and codling all perishing, although at very 

 different intervals. In order to get a more precise relation between the 

 temperature and the growth it would be necessary to maintain the 

 temperature nearly uniform in each of the tanks throughout, or at all 

 events to reduce very greatly the rapidity of the alterations. The 

 question of food is also one that would, in any circumstances, give rise to 

 difficulty, and yet it is evidently one of much importance. It is not 

 easy procuring the natural food of the fishes and supplying it in due 

 proportions. 



It appears that the influence of temperature is active in modifying the 

 rate of growth by acting directly upon the metabolism of the fish, and 



