HARDWICKE'S SCIENCE-GOSSIP. 



J93 



LIFE BELOW THE ICE. 



UCH has been writ- 

 ten of late on the 

 destruction of 

 birds and the larva; 

 of insects by the 

 long continued 

 frost of the past 

 winter. Can any 

 of your scientific 

 readers give a 

 satisfactory expla- 

 nation of how it 

 is that fish can 

 exist below the ice 

 for lengthened 

 periods, and how, 

 under such cir- 

 cumstances, their 

 respiration is main- 

 tained ? Many of 

 our mountain tarns 

 in this neighbourhood have been completely covered 

 with ice, in some instances of more than two feet in 

 thickness, for a period of not less than three months. 

 The fish do not appear, however, to have diminished 

 in numbers, and those captured shortly after the ice 

 broke up were in excellent condition. 



We know that fish are dependent for their respira- 

 tion on the oxygen which water holds loosely in 

 solution. By a movement of deglutition the water 

 taken in by the mouth is passed from the pharynx 

 into the gills, and, while escaping posteriorly through 

 the membranous laminae of the latter, gives off its 

 loose oxygen, which purifies the venous blood con- 

 tained in the delicate vessels by which the laminae 

 are traversed. It is a generally accepted fact that 

 this admixture of oxygen with water is principally 

 brought about by the perpetual agitation of the latter 

 by storms, currents, Sec. In the tanks of our public 

 aquaria it is necessary to have a continual circulation 

 of fresh water, or a rush of air into each tank, to 

 prevent the fish being suffocated. In the Brighton 

 Aquarium air is pumped into the tanks. In streams, 

 in lochs, partially frozen over, in lochs entirely 

 covered with ice, but supplied with large and in- 

 No. 177. 



exhaustible feeders, it is not difficult to understand 

 how the supply of air is kept up. Many tarns, how- 

 ever, in our lakeland, Smallwater, for instance, have 

 no stream falling into them. Completely sealed by 

 ice for months, their waters have had no agitation in 

 contact with the air. Their supply of water is 

 drawn from subterranean springs, and that it was 

 very scanty, owing to the absence of rain and low 

 temperature, is proved by the fact that no water 

 escaped from the tarns by these outlets. Many of 

 those tarns teem with fish, which must surely, sooner 

 or later, absorb all the loose oxygen with which the 

 water was charged previous to its being locked by 

 ice. The demand for oxygen is unceasing, and if the 

 usually accepted theory of aquatic existence is correct, 

 what is the source of this supply which the experience 

 of the late frost would almost lead us to believe to be 

 inexhaustible ? 



I am aware of the exquisite balance which is 

 maintained between land animal and plant life, and 

 which equally exists between aquatic animal and 

 vegetable life, by which the latter decomposes the 

 carbonic acid given off by animals, and produces 

 oxygen, which in its turn aerates the water. This 

 process, however, can only take place under the 

 influence of light, so that in the circumstances we are 

 considering it must be to a large extent in abeyance, 

 for in addition to two feet of ice covering the tarns, 

 there have been six or eight inches of snow, which 

 must have robbed plant life below of nearly, if not of 

 all, sun light. Arctic travellers have told us that 

 when a hole is made in the ice, fish congregate in 

 large numbers in its vicinity, and come to the surface 

 for air ; but is it not more likely that they are 

 attracted by the light thus admitted, just in the 

 same manner as salmon and other fish, fascinated by 

 the light of a torch, will lie close under it and suffer 

 themselves to be captured by the unscrupulous poacher? 

 Were they pining for air, it is difficult to believe that 

 life could be maintained. In the northern latitudes, 

 moreover, there are vast tracts of open water in com- 

 munication with that which is ice-bound. There are 

 great ocean currents, just as there are atmospheric 

 currents, and by the former no doubt an unfailing 

 supply of oxygenated water is being constantly carried 



