306 ON AN EXPERIMENT IN THE KEEPING OF SALMON 



Living Shrimps {Crangoii). 

 „ Prawns {Palaemon). 



„ Pandalus anmdicornis and P. hrevirostris. 

 Cut Squid (Loligo). 

 „ Scallop (Fecfen). 

 Living Pollack [Gadus pollachlus), about 2 inches long. 

 „ Gobies (Gobius minutus and G. ruthensparri). 

 Cut Plaice {Pleuronectes platessa). 



The salmon were seen by Dr. Allen to take hold of some of the 

 shrimps, though afterwards releasing them, and to show a certain 

 interest in some of the small fish. But there was no evidence of their 

 having swallowed any of these objects of food, and the only conclusion 

 to be drawn is that they entirely refused them. Two of the smolt& 

 were kept for some time in a separate tank with two bass as 

 companions, the only food offered them being shrimps, prawns, and 

 gobies. Although the latter experiment was not conclusive, no 

 evidence that any of these had been eaten by the salmon was- 

 obtained. On the first two or three days, while the smolts were- 

 still in fresh water, it was once or twice observed that fragments 

 of the prepared foods (not liver) were picked up by them after 

 reaching the bottom of the tank ; but this never occurred afterwards, 

 and even the living Nereis, which happened to reach the bottom, were 

 allowed to remain there crawling about, without the salmon paying 

 any attention to them. In marked contrast to this, some Eainbow 

 Trout (Salmo irideus), which the Duke of Bedford has also sent 

 to the Laboratory from Endsleigh, will connnonly follow their food to 

 the bottom, and continue to pick it up for some time after it has 

 settled. These Kainbows, too, easily adapt themselves in sea water 

 to the cut Squid {Loligo), and some other foods ordinarily given to- 

 the marine fishes. 



Fird Spavming, 1906-7. — Signs of approaching maturity became 

 apparent in the smolts towards the end of October, 1906, i.e. eight 

 months after they were first passed into sea water. On October 31st 

 and November ] st it was observed that scarcely any food was taken, 

 and in some cases what was taken into the mouth was discarded again. 

 During the previous week the fish had been growing darker in colour. 

 They began to frequent the bottom of the tank and to lie there 

 heavily. One of them lost the upright position, and died in a day or 

 two afterwards (November 4th). It was accordingly decided to pass 

 sixteen of the more advanced ones into fresh water. The process was 

 begun on November 6th, and the change was made in a very similar 

 manner to the reverse one in the preceding March. The time allowed 



