166 



Part III. — Twenty-second Annual Report 



The same is true of Tank No. 2, except, as formerly explained, the 

 temperature here was generally slightly higher owing to its being nearer 

 the stove. Into this tank were placed fiteen whitings, three haddocks, 

 two common dabs, and a starry ray ; a sand-eel was also present at first, 

 but, as in the other tank, it soon disappeared. The particulars of these 

 fishes are given in the accompanying Table. Three of the whitings are 

 not included in the final column and averages ; No. 13 was found in the 

 second period to have the tail and one of the eyes diseased, and its 

 growth had been thus interferred with, No. 14 was transferred to the 

 warm tank as already described, and No. 15 was found dead when thirty- 

 five days of the second period had elapsed, and it then measured 134mm. 

 In the first hundred days, with a mean temperature of 5" 2 C, the 

 increments varied from 14 to 22mm., the mean being 17*7mm., or 

 1 '7mm. above that for Tank No. 1, a difference probably related to the some- 

 what higher mean temperature ('7 C). As a rule the greatest increase 

 was among the smaller fishes. In the second period of 55 days, with a 

 mean temperature of 9'2 C. (48 - 6 F.), the increments ranged in different 

 cases from 10 to 17mm., and the mean was 14mm., as compared with 

 13*86 in Tank No. 1, the mean for ten days being 2*55, as compared with 

 2*52 — almost precisely the same. It will be seen from the tables that 

 the mean temperature of the two tanks in the second period were also 

 practically identical, differing by only *1 C, but the difference was in 

 favour of Tank No. 1, into which the sunshine entered more freely. 



The haddocks did not thrive so well compared with the one in Tank No. 1, 

 and they all died early in the second period. The mean increment in 

 the hundred days was 18 -6mm., as compared with 27mm. in Tank No. 1, 

 the mean for the ten days being l-86mm. against 2'7mm. One of these 

 haddocks, 199mm. long, perished by being placed in warmer water as 

 previously described ; it was well nourished, its weight being 67 "5 

 grammes, while the mean weight of haddocks of the same size is 65*7 

 grammes (see Table, p. 226). One of the others died 18 days after the 

 measurement recorded, and it was then 216mm. long, an increase of 5m. 



Of the two common dabs, the smaller grew quickly and the larger 

 slowly. In the first period the former increased by 22m. and the latter 

 by only 7mm. ; in the second period the smaller increased by 22m. 

 again, and the larger by only 3mm., the growth as with the round fishes 

 being about twice quicker in the higher temperature of the second period. 

 The small one increased in the hundred days by 44mm., or 1} inches, the 

 mean rate being 2*84mm. per ten days, while the increase of the larger 

 one amounted in the 155 days to only 10mm., or § of an inch, the mean 

 for ten days being only 0*07mm. They were both females. 



The starry ray did not grow at all ; during the first period it just 

 maintained its breadth, and in the second it lost about 3mm. in the same 

 dimension. Its loss of weight must have been relatively greater because 

 it became very attenuated, and it was no doubt owing to lack of proper 

 food. 



In Tank No. 3 an endeavour was made to maintain a temperature 

 intermediate between that of Tanks Nos. 1 and 2 and Tank No. 4, but as 

 previously mentioned the variations were considerable, and the results in 

 this tank were not so satisfactory. It appears moreover probable that in 

 the endeavours to adjust the supply of hot and cold water the circulation 

 was diminished. For some reason or another four of the whitings and 

 five of the codlings put in died a short time after the experiment was 

 begun, and these are not included in the accompanying Table, which 

 gives the particulars regarding the rest of the fish. Two haddocks which 

 were placed in the tank also died : the autopsy revealed no apparent 



