368 Mr. R. Warington's Notes on Animals in small Aquaria. 



will tend to show : — In a small aquarium that had had gold-fish 

 kept in it for a length of time^ but which had been removed into 

 one of larger dimensions and more fully exposed to the light, an 

 enormous number of the Hydra fusca were observed to have 

 made their appearance very soon after this removal. Wishing 

 therefore to ascertain if the appearance and rapid increase of 

 these polypes had been prevented by the gold-fish, the following 

 experiments were made : — Fifteen individuals of the Hydra fusca 

 were placed in the aquarium containing the gold-fish, but they 

 very soon disappeared, having I presume been devoured by the 

 fish ; a second fifteen were then introduced, but with the same 

 result. At the same time as this experiment was made, fifteen 

 hydras were placed in a tank containing four minnows (Leuciscus 

 Phoocinus) and a pair of small eels, but as the minnows did not 

 appear to touch them, the same number of polypes being 

 counted over several times during a period of three weeks, they 

 were soon forgotten altogether. After a space of about seven 

 mouths had elapsed from this time, the minnows were observed 

 to assume a most extraordinary aspect, the head appeared very 

 much swollen, and the eyes of all of them looked as though 

 starting out of their heads, being forced upwards and in an out- 

 ward direction and much enlarged ; by degrees the gills of some 

 of them became streaked with bloody markings, and this gra- 

 dually extended to the base of the pectoral fins. The whole ap- 

 pearance was most distressing to contemplate, particularly as it 

 was impossible, from ignorance of the cause, to adopt any reme- 

 dial measures. Judging from their appearance my impression 

 was that they had been poisoned, and assuming that it must 

 have arisen from something putrescent which they might have 

 raked out of the materials at the bottom of the aquarium, the 

 whole of the water was drawn off" clear by a siphon, the gravel 

 and sand thoroughly washed, and everything replaced in the tank 

 with the fish ; no improvement however appeared to follow, the 

 fish got worse and ultimately died. This was in June 1853. 

 Before this extraordinary change came on, the fish had been ob- 

 served to cluster together in one particular secluded spot, and 

 rarely came out as they had been accustomed to do, and when 

 they did venture forth they rubbed or jerked themselves with much 

 force against the gravel and rock-work, as though something was 

 irritating the skin ; nothing however was visible. I had had these 

 fish for about eighteen months in the same aquarium. As the 

 water was perfectly bright and clear, and free from all odour or 

 unpleasant taste, I procured six fresh minnows and placed them 

 in the tank; for about ten days they appeared to be pretty 

 healthy ; they did not however swim about freely, but herded 

 together in one corner of the aquarium, and then the same ex- 



