HARD WICKE'S SCIENCE- G OSSIP. 



267 



FROZEN-OVER FISH-PONDS. 

 By W. A. Lloyd. 



IN the September number of Science-Gossip, 

 pages 193, 194, there is an inquiry by a writer 

 signing " Piscator," respecting the manner in which 

 fish can breathe when the water they are in is 

 thickly and completely frozen-over for prolonged 

 periods. Water, of course, is valueless for respiratory 

 purposes, unless it contains a sufficient quantity of 

 atmospheric air, a large amount of which consists 

 of the oxygen which is necessary to revivify the blood 

 of the creatures which breathe such water, and thus, 

 in the manner which the writer correctly describes, 

 the carbonised blood enters the gills at one part, 

 and in a decarbonised, or purified state, leaves them 

 at another part. These gills are arranged, in most or 

 many water-breathing animals, like combs, the teeth 

 of which the water surrounds, and supposing each 

 tooth to be a tube through which the blood or other 

 vital fluid flows, the walls of the tooth, or tube, 

 are made so thin, that the blood within and the water 

 without, can touch each other freely without mixing, 

 one purifying the other, this being done in this beauti- 

 fully contrived apparatus, in a small bulk, packed, in 

 the case of fishes, just within the gill cover in the rear 

 and sides of the head. The blood is set in motion, or 

 circulated round and round in the creature's body, by the 

 pulsations of the heart, while the surrounding water is 

 similarly caused to flow, and to circulate, by the constant 

 opening and closing of the mouth, these two pumps 

 (the mouth and the heart) thus continuously working 

 in conjunction with each other, and absolutely never 

 stopping, so long as the creature lives. And, to 

 serve both pumps, the water in which the fish lives 

 has the property of absorbing by contact a given 

 amount of air from the atmosphere at given tem- 

 peratures. When the temperature is high, the 

 quantity of air which water can take up and retain is 

 much less than when it is cold. Thus, in hot weather, 

 we often see a fish in a glass globe or other vessel, 

 gulping water from the very surface of the fluid, because 

 there it is in immediate contact with the atmosphere 

 where the aeration is greatest, and thus the instinct 

 of the fish teaches it to pass over its gills this fluid 

 which has thus been oxygenated, in preference to 

 going below for it, where the water is less aerated, 

 and therefore, in effect, less pure. But, at a colder 

 season, the same fish, in the same water, in the same 

 vessel, in the same spot, and under the same circum- 

 stances, in all respects except temperature, may be 

 observed less painfully (because in a less constrained 

 position demanding exertion all to one end) swimming 

 about below the surface, with the double pumps at work 

 as ceaselessly as ever. Certainly, therefore, it might be 

 supposed that the fish would die, if, on the one hand, 

 the water were to be so warm that it would not retain 

 enough air in solution, no matter how fast and well 

 the mouth-pump worked. And, on the other hand, it 



might as truly be imagined that the fish would no 

 live — no matter how favourable the temperature 

 might be for the absorption and retention of air — if no 

 air could get to the water by its being for a consider- 

 able time closely covered over, as for example, by 

 ice. But, even though the water is thus fast sealed 

 up for a long time by a thick covering of ice, its 

 coolness, which the ice imparts, tends to cause it to 

 retain, the more easily, such air as it does already 

 contain in solution. And then, too, cold retards the 

 vital energies of the fish, and causes its respiration to 

 be slower, and the need for the air to be consequently 

 less, so that here are two favourable conjunctions — 

 greater supply and less demand. 



But is it absolutely certain that such frozen-up 

 lakes have no communication with open water? 

 How, and with what streams, are these ponds or 

 tarns fed or supplied in summer ? Cannot they be 

 traced in winter, and, if so, is it quite sure that no 

 water runs through them, or beneath their ice, at 

 that time? It would be not very difficult for an 

 ingenious person to detect if any current exists beneath 

 the surface of any ice-bound pieces of water. I could 

 do so in the coming winter with an absolute certainty 

 of obtaining correct results. For example, vertical 

 holes might be bored in the ice, and in these orifices 

 might be firmly inserted wide glass tubes, say of an 

 inch and a half internal bore, with both ends open, 

 one in the water below, and one in the air above. And 

 in such tubes, supported or hung by light rods or wires, 

 could be placed various indexes, some for showing 

 vertical motion, others to point out horizontal currents, 

 and some to exhibit rotary or obliquely-running streams. 

 It would be a very cheap thing to have three, or even 

 more, of such tubes, each having its own office. There 

 come other considerations, too. Thus, if by reason 

 of a slower respiration caused by a lower temperature, 

 there be less energy, there is also a smaller consump- 

 tion of food to be thought of, and less excrement to 

 be voided, and less sullying of the water thereby, 

 accompanied by smaller demand for oxygen to consume 

 or get rid of the results of such voiding. Added to 

 this, the water is, because of its icy covering, much less 

 liable to receive excrementitious substances from land 

 animals at or near its margin, or from birds flying over 

 it, and indeed all dirt is hindered from entering by 

 such covering, every small prevention of impurity 

 being thus of consequence. 



Certainly, a thick coating of ice would, especially 

 if covered with snow, also hinder the penetration of 

 light, and the growth would thus be partly debarred 

 of the influence of the subaquatic vegetation which so 

 much and indeed indispensably assists the purity and 

 decarbonisation of the water. But this would not 

 amount to actual darkness and complete hindrance 

 of the office of the plants. It would only be a retarda- 

 tion, and one, moreover, occurring when it could best 

 be afforded. 



Connected with this subject is the wonderful pro- 



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