SEA-FISHERIES LABORATORY. 101 



through the tanks, or little or no circulation but an abundance 

 of growing vegetation. Aeration with a force pump has much 

 the same result as the action of growing vegetation. Should 

 the circulation stop through any cause, the animals in a tank 

 which has no vegetation die off in the ratio of their vitality. 

 Organisms such as Noctiluca have been kept alive in a perfect lv 

 still tank for a month. An aquarium with growing vegetation 

 in it requires practically no circulation. We have a small fresh- 

 water aquarium that was started many years ago in connection 

 with the classes for school teachers. Vegetation was induced 

 to grow and it still continues in a nourishing condition. All 

 that is needed is a cupful of tap water added at intervals to make 

 up the loss from evaporation. Various organisms, such as 

 Hydra, Copepoda, Cladocera and Limnaea, have become estab- 

 lished and one generation succeeds another. A freshwater 

 stickleback placed in the jar in August, 1920, remains alive and 

 healthy after a lapse of eight months. Weeds and Diatoms, 

 in the presence of light, are the chief aerators of the sea. The 

 water is never perfectly still and the pelagic organisms are 

 constantly moving up and down in it. A surface film of oil 

 will not cut off the light sufficiently to prevent the algae and 

 Diatoms keeping up the aeration. Its lighter specific gravity 

 will also keep it clear of the pelagic organisms. When the film 

 of oil stranded on the sands, the Navicula, and other species of 

 Diatoms which form conspicuous brownish patches on the surface, 

 were not destroyed although the film was spread over them. 

 There is as yet, so far as Barrow Channel is concerned, no 

 indication that the oil trade and the extending use hi the con- 

 sumption of fuel oil has had any harmful effect on the fauna 

 and flora. The chief engineer of one of the tankers making 

 frequent voyages to Barrow tells me there need be no discharge 

 of oil or fuel oil into the water. That would be regarded as 

 uneconomical by the owners and add to the running costs of the 

 vessel. The oil is recoverable from the refuse. 



