274 DR. F. DAY ON INDIAN FRESHWATER FISHES. [May 14, 



5. Observations on some of the Freshwater Fishes of India. 

 By Francis Day, F.L.S., F.Z.S. 



I have done myself the pleasure of transmitting to the Society, by 

 the steamer of March from Madras, nineteen living specimens of 

 Ophiocephalidse, commonly knovra in India as "Walking Fishes"*. 

 They form a portion of Cuvier's great family of Acanthopterygian 

 Labyrinthici, now subdivided by Bleeker, who has placed the Ophio- 

 cephalidae, including the genus Channa, independent. It appears to 

 me that this may be a good opportunity to draw especial attention to 

 some points which seem to have been sometimes misinterpreted with 

 reference to these and allied fishes ; for, notwithstanding anatomical 

 differences, the Ophiocephalidse have much in common with the true 

 Labyrinthici. 



The interesting subject of the respiration of Indian freshwater 

 fishes still needs much investigation ; and I regret that at present I 

 have not sufficient leisure to work out the required desiderata. 



Most species undoubtedly respire the air in solution in the water, 

 and find it sufficient — excepting under peculiar circumstances, when 

 they obtain it direct from the atmosphere. But there are others, 

 which may be called aerial, or compound breathers, which never 

 obtain air for any length of time from the water alone, but require 

 it direct and undiluted, no matter how cool or charged with air the 

 water may be, and if unable to inhale atmospheric air are simply 

 drowned. Those who keep aquaria in India can easily detect these 

 different methods of respiration. In the Carp {Puntius), for instance, 

 the mouth is frequently opened, and the gills are in constant motion, 

 whilst they rarely rise to the surface, unless they are ill, or the water 

 is either very hot or vitiated. The reverse is seeu with some of the 

 Acanthopterygians and a few of the Loaches and Siluroids, which do 

 not move their gills so much in dirty water as in clean ; and if the 

 water is what they are accustomed to live in, viz. muddy, or even 

 filthy, the gills are comparatively at rest : but these fishes may occa- 

 sionally be seen rising slowly to the surface, where they discharge a 

 bubble of air, and then sink down again. This bubble has probably 

 had some of the oxygen removed from it, and is thus rendered unfit 

 to support respiration. Dr. Carpenter f in Europe has observed 

 that in some " fishes, especially such as inhabit small collections of 

 fresh water, whose temperature is liable to be considerably raised 

 during the heat of summer, the mucous lining of the alimentary 

 canal appears to serve as an additional organ of respiration ; for such 

 fishes are frequently seen to rise to the surface and swallow air, 

 which is subsequently discharged by the anus, with a large quantity 

 of carbonic acid substituted for its oxygen. This is the case, for 

 example, with the Cobitis (Loach) ; and it would seem as if under 

 these circumstances some such supplementary means is required for 



* Of these, six {Ophiocephalus gacJiua) arrived alive on the 21st of May, but 

 not in good condition, and died very shortly afterwards. See Appendix. — P. L. S. 

 t Principles of Comparative Physiology, ed. iv. 1854, p. 324. 



1 



