10 MARINE AND FISHERIES 



1-2 EDWARD VII., A. 1902 



was a tall cylindrical museum jar (with an external diameter of 6 inches) the water in 

 which stood 8f inches high. The experiment began at 10 a. m. At 5 p. m. the fish in 

 the tall vessel was lying on its side in a dying condition. The next morning it was of 

 course dead, while the one in the shallow pan was quite lively. The same results 

 occurred whenever this experiment was repeated. 



Such experiments evidently show that ventilation or aeration of water is as 

 important in fish-respiration as ventilation of air is in mammalian respiration. They 

 show that ventilation goes on naturally and readily in the shallow water of a broad flat 

 vessel. In such a vessel, a large surface of water is exposed to the air. As the oxygen 

 dissolved in the water gets used up by the fish, fresh oxygen is absorbed from the air, 

 the absorption being promoted by the movements of the fish, which agitates the water 

 and exposes a fresh surface to the air. On the other hand, the water in a tall narrow 

 vessel has a comparatively small surface exposed to the air, and a fish, usually lying at 

 the bottom, does not agitate the surface so as to promote aeration of the water. These 

 experiments throw lighii on how trout can live in very tiny streams of water in dry 

 weather, and they explain also how minnows can live all day long in a little water in 

 the bottom of a fishing boat. 



The second question, ' should large quantities of water, or comparatively small 

 quantities of water be used in the experiments ?' was not so easily answered. The 

 quantity was, of course, found to vary with the extent to which the water was ventilated 

 or aerated. If artificial ventilation were applied to the water, then a relatively small 

 volume would do ; if no artificial ventilat on were applied, then, of course, a much 

 larger quantity of water had to be used, and it had to be placed in a broad shallow dish. 



In connection with this subject, a number of experiments were tried for the purpose 

 of determining the length of time that unit weight of fish (1 gram) could live in unit 

 volume (1 c.c.) of unaerated water. Fish were weighed and placed separately in closed 

 vessels completely filled wit,h a known volume of water, and the length of time they 

 lived was carefully observed. The following was a typical experiment : Weight of fish, 

 76 grams ; volume of water, 5,530 cubic centimetres ; lived six hours. Therefore, 

 1 gram weight of fish lived in 1 c.c. of unaerated water for about five minutes. 



Ten similar experiments on rock bass of different sizes gave seven minutes as the 

 average time during which unit weight of fish could live in unit volume of unventilated 

 water, the range being five minutes as the minimum and nine minutes as the maximum. 

 The temperature of the tap water with which these experiments were conducted was 

 22° C. When the water was cooled down to 4° C, the fish lived for a shorter time. 

 When the temperature was raised to 32° C, they lived for a shorter time also. 



These figures for the duration of life in fish confined in a limited quantity of water 

 are interesting when compared with those obtained by Paul Bert for mammals 

 breathing a limited quantity of air. Five experiments by this observer gave eight 

 minutes as the average length of time during which unit weight of mammal (1 gram) 

 lived in unit volume (1 cubic centimetre) of confined or unventilated air.* Mammals, 

 therefore, use about six times as much oxygen as fish do in the same length of time. 



These experiments suggested the possibility of determining the smallest amount of 

 water in which a fish of a given weight could live for many hours or even days, on the 

 supposition that this minimum quantity could be kept perfectly ventilated. Of course 

 a fish requires something more to maintain life than aerated water. Free movement is 

 essential, not to speak of food ; but apart from these and similar considerations it 

 seemed worth while to conduct an experiment or two on the respiration of a fish in a 

 minimum amount of water. 



With this object in view, a perch ( Perca flavescens, Mitchell; was placed in 600 

 cubic centimetres of water in a jar, and arranged so that a continuous stream of air was 

 bubbled through it. There was just enough water to cover the fish. Its position in the 

 bottle tended to throw the animal on one side, in which position it seemed to stiflfen, 

 for, at the end of 24 hours, it was removed from its prison with its body slightly curved 

 to one side. In three or four hours it could swim slowly about the aquarium, but for 



*Le9ons sur la physiol. comp. de la respiration," Paris, 1870, page .510, quoted in Heliiifer's Text-book 

 of Physiology, vol. i, page 743. 



