18G8.] DR. F. DAY ON INDIAN FRESHWATER FISHES. 275 



carrying on the respiratory process with unusual activity," This 

 occasional swallowing of atmospheric air is also perceptible when the 

 water becomes foul, or when the amount of air in it appears to be 

 almost exhausted by its inhabitants ; for instance, in three days in 

 May 1867, the heat of the atmosphere and of the water in an 

 aquarium at Madras was as follows : — 



Yet notwithstanding this heat the contained fishes did well, although 

 they swam near the surface to obtain more oxygen, and sometimes 

 appeared even to take in atmospheric air directly. Native fishermen 

 maintain that the middle of the day is the best time for netting 

 freshwater species, as they are then near the surface, no doubt from 

 the heat of the water, and its consequent deficiency of air. 



In India, instead of discharging the previously inhaled air by the 

 anus, the fish appear to do so by the mouth ; at all events the com- 

 pound breathers adopt this process. Sometimes they do not emit 

 any bubble, but seem only to take in air, whilst' at other times the 

 bubble is discharged at the bottom of the water ; this is especially 

 apparent after they have taken food. The purely water-breathers, 

 if the term is admissible, can live without rising to the surface, un- 

 less under peculiar circumstances, whilst the compound breathers, as 

 already mentioned, expire in a longer or shorter period if unable to 

 reach the atmospheric air. The difference between the respiration 

 of the compound breather and that of the water-breather is very 

 apparent when they are lying side by side on the moist sand at the 

 bottom of an aquarium. For instance, the Macrones tengara keeps 

 its gills in constant excited motion, while the Ophiocephalidae 

 scarcely move theirs, but at intervals rise to the surface, open their 

 mouths, and take in air. This latter phenomenon, viz. breathing the 

 air pure, and not subsequent to its solution in the water, is especially 

 apparent in some species, such as the Polyacanthus cupamis, Cuv. & 

 Val., which dart up suddenly to the surface, descending again as 

 rapidly into the rockwork in which they delight to make their home, 

 and where they keep all other species at bay, and even fight amongst 

 themselves for the possession of a coveted corner. Loaches (of the 

 genus Platacanthus) also ascend in a similar manner to obtain air. 

 The earliest observation on this peculiar mode of respiration which has 

 fallen under my notice is made by Dr. Garden*, M.D., F.R.S., in a 

 letter from Charles Town, South Carolina, dated August 14th, 1774, 

 where he states, respecting the Electrical Eel, that its pectoral 

 fins seem to be chiefly used for supporting and raising the fish's 

 head when he wants to breathe, which he does every four or five 

 minutes, by raising his mouth out of the water. With reference to 



* Philosophical Transactions of the Eoyal Society of Loudon, 1775, vol. Ixv. 

 p. 102. 



