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Show 274 DR. F. DAY ON INDIAN FRESHWATER FISHES. [May 14, 5. Observations on some of the Freshwater Fishes of India. B y F R A N C I S D A Y , 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 ot OphiocephalidEe, commonly known in India as " Walking lishes . They form a portion of Cuvier's great family of Acanthopterygian Labyrinthici, now subdivided by Bleeker, who has placed the Ophio-cephalida**, 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, aud 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 seen 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 occasionally 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 alimentarv 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 f example, with the Cobitis (Loach) ; and it would seem as if ' 1 these circumstances some such supplementary means is reauirp 1 f * Of these, six {Ophiocephalus gachua) arrived alive on the 21st of TVT-not in good condition, and died very shortly afterwards. See Appendix - T P \ « t Principles of Comparative Physiology, ed. iv. 1854, p. 324. ' *••*-"• "> |