1864.] ON PISCICULTURE. 131 



The proper temperature of the water, both in and out of doors 

 ought to range from 40° to 50°. Mr. Ponder's observations tell 

 him that at this temperature it requires thirty-five days for the 

 eyes to appear, and that they hatch out fourteen days afterwards. 

 The same result has been obtained by him for two successive 

 seasons with very little variation. Again, he has observed that 

 when the temperature was 50° (in the spring of the year) the 

 eyes of the fish were visible in twenty-six days, and that he 

 hatched them out in ten days afterwards. Lay it down 

 however for an axiom, that the higher the temperature for the 

 egg the weaker the fish produced from the egg. Anything above 

 50° is weakeninsr. 



The first fish hatched out from a batch are the weakest, the last 

 are the healthiest ; when however they once begin to hatch, they 

 will come out all in a mass, two, three, or four thousand of a 

 morning. The proper temperature for trout and salmon eggs is 

 40° to 50°. 



Grayling however appear to be an exception to this rule. Mr. 

 Ponder has obtained a fair supply of the ova of these fish, which 

 the Thames Angling Preservation Society are introducing in the 

 Thames. The quantity obtained amounted to between fifteen and 

 twenty thousand ; and though several of these died, for they are 

 most delicate things to carry, the remainder did very well. They 

 are much more delicate than trout-ova, both in appearance and 

 hatching, and seem to die at the least provocation. They are beau- 

 tifully transparent, and, when viewed in the sun, of a lovely opales- 

 cent hue. He has discovered about these a most interesting, and 

 I believe, a novel fact. The body of the fish is perfectly visible 

 in nine days, and the fish will actually hatch out of the egg in 

 fourteen days. 



All difficulties and trouble with the eggs having been overcome, 

 we are at length rewarded by seeing the young fish begin to come 

 out of the egg. At this time the tail of the fish may be observed 

 moving from side to side with a rapid vibratory movement inside 

 the egg. The young fish, when hatched, increase in size daily ; 

 and the darkening of the transparent substance which would 

 eventually be the body, and the development of the fins, have al- 

 ready proved one fact, and this (as the question has frequently been 

 put to me) I shall venture now to mention. The eggs do not 

 grow — i. e., they do not increase in circumference or in diame- 



