M ISC ELLA NEO US NO TES. 1 9;-) 



No. XII.— NOTES ON THE RESPIRATION OF THE MURRAL 

 {OPHIOCEPHALIDM). 



In describing the niurral on page 233 of the "Rod in India" (3rd 

 Edition, 1897), Mr. Thomas writes as follows : — 



" They may be seen coming np to the surface continually, exhaling a 

 bubble and taking in a mouthful of fresh air, and they have an air cavity 

 for the storage of the fresh air. If confined in a globe or other vessel with 

 a net stretched across a little below the surface of the water, so as to 

 prevent them from breathing the atmospheric air direct, they will die from 

 not being able to oxygenate their blood, however fully supplied with oxygen 

 the water may be."' 



For the last four years I have made somewhat inchoate observations on 

 the habits of murral. One result of these in brief is the conclusion, that 

 the auxiliary breathing apparatus of the family Ophiocephalidte is, as 

 Mr. Thomas observes, indispensable, and that the fish will die directly its 

 breathing is confined to the use of its gill filaments, but only in certain condi- 

 tions of the water in which it is livinc/. Jn October 1912, for instance, a 

 number of murral were caught in running water at a temperature of about 

 78° F. at Dinanagar in the Punjab. They were at that time rising to the 

 surface continually in order to inhale the outer air. They were transferred 

 to a rock-hewn tank at the top of a hill in Nurpur Fort some thirty miles 

 away. Here at fii"st they continued to rise to the surface, but as the winter 

 drew on and the water temperature in the tank fell to 50° F. and below 

 they ceased to rise altogether. It was certain that they could not have 

 escaped, and subsequent observations showed that they were all there, 

 yet the surface never shewed a "rise." In the summer they were 

 rising as merrily as ever. But in the following winter they went down 

 again and remained at the bottom as did their progeny, for they bred 

 freely. 



Meanwhile, on 23rd November 1913, two murral were placed in a live car 

 in running water : they were placed at the bottom of a pool about six feet 

 deep in such a manner that they could not rise to within three feet of 

 the surface. The fish were respectively 18" and 12" long. They were 

 left at the bottom 24 hours and were perfectly well at the end of the 

 experiment. 



Since then I have had many proofs that murral need not come to the 

 surface provided that the water is sufficiently cold. It is fairly certain, 

 however, that Mr. Thomas and other Madras observers have never had to 

 deal with the fish in water cold enough to render them independent of the 

 air cavity. Hitherto all observations have been made in waters so warm as 

 to make the fish absolutely dependent on this store of surplus oxygen 

 which needs constant replenishment if it is to be drawn upon : and the 

 conckision, that unless it could rise to the surface, it would die, "however 

 fully supplied with oxygen the water may be", was perfectly legitimate 

 and natural. 



Nevertheless, I believe that the air cavity is only an auxiliary apparatus to 

 be called into use when the supply of oxygen obtainable through the gills 

 is insuflicient, and that this characteristic has only escaped notice because 

 observations have never been made in waters, like those of the Punjab, 

 whose low temperature in winter enables them to absorb large quantities of 

 oxygen by atmospheric pressure. 



The fact that water will absorb oxygen and nitrogen, in other words will 

 become "saturated with air" when it is exposed to the atmosphere, is well 

 known. Not all field naturalists are aware that the degree of absorption 

 varies in inverse ratio to the temperature. Roughly speaking, one litre of 



