44 A Brief History of a River Tank. 



this long period ; but I think they have grown, though cer- 

 tainly very little. They are tame and lazy, and happy 

 and beautiful, and they have served an important purpose to 

 me besides the adornment of the hall, for, after their seven 

 years' habitation of this tank, having had two years of active 

 experimentalizing previously, they have solved the problem of 

 the cubic space required by a fish for breathing room, and I shall 

 be able to give a safe rule for the guidance of all cultivators of 

 aquaria. 1 have arrived at the maximum capacity of my tank 

 in various ways. One way was to introduce occasionally a 

 few new fishes. As common carp abound in a pond close by, a 

 good many have had temporary residence in the tank. Min- 

 nows have been used in the same way, and I have also added 

 gold carp, and other fishes which are generally tolerably 

 adaptable in constitution. But it always happened that when 

 the fishes exceeded a certain number there were signs of dis- 

 tress. I could not begin changing the water to obviate this, 

 because that would be to annihilate the natural system "at 

 one fell swoop. " No, the water has never been changed 

 during the whole seven years, though, of course, it is necessary 

 occasionally to make good the loss by evaporation. But I did 

 try on a few occasions of extreme distress to aerate the water 

 by the use of a garden syringe. Charging this from the tank 

 the water was ejected back with force through some slight 

 atmospheric distance, carrying streams of bubbles to the bot- 

 tom of the vessel. This would be amusing, because the fishes 

 would rush at the streams of bubbles and absolutely gulp 

 them; but it was fagging work, and, of course, was only per- 

 formed by impulse and not by system. ' The end of every one 

 of these experiments was the same. One or two of the newly 

 introduced fishes would, after the lapse of about a fortnight, be 

 found dead and " floating on its watery bier.-" Next a few more 

 would die, and so on till the whole of the new comers were 

 cleared off, and the old, well-seasoned members of the ' c happy 

 family " remained unhurt, but breathing more freely for the 

 relief, and no doubt rejoicing to have got rid of the innova- 

 tors. Suppose now that you have some gold fishes, averaging- 

 four to six inches in length, to preserve for any length of 

 time by the natural system, and under circumstances at all 

 resembling the case here described, for half-a-dozen of those 

 fishes you must have a vessel holding at least twenty-four 

 gallons of water. The smallest of your fishes will need three 

 gallons, all larger four or five gallons. Most of the failures in 

 tank management have resulted from over-stocking, but the 

 modification of the light is an equally important matter. 



The natural system can be carried out in marine tanks in 

 much the same manner as in river tanks, though, of course, 



