44 PACKING THE TROUT OVA. 



about the thickness of a layer of ova. So soon as the surplus water 

 has been drained by force out of the moss, the pad is ready, and 

 the trays, in lots of eighteen, are carried down to the egg-packing 

 room. 



The three great considerations in supplying ova satisfactorily 

 are the class of ova selected, the age of the embryo at the date of 

 packing, and the temperature maintained during the whole time 

 of transportation. 



CLASS OF OVA. 



By class of ova I mean, not only the locality from which 

 the spawners were procured, but, and most particularly, the 

 age of the spawners from which the ova was obtained. The 

 Howietoun experiments have pretty conclusively proved that 

 the individuality of a local race is very generally main- 

 tained in the offspring of the oldest parents, while the diversity 

 common to the species is exhibited in a very large pro- 

 portion of the fry, the produce of young fish. Therefore, while 

 all trout are probably merely local races of fario, and the fry 

 produced from young fish of any local race, if transported, rapidly 

 become undistinguishable from the aborigines, the produce of old 

 spawners retain so much of the characteristics of their parents as 

 to become unsuited to the smaller and more rapid rivers and for 

 many cold and barren highland lochs. Thus there is room for the 

 exercise of great skill in the selection of ova according to the age 

 of the parent fish and the nature of the water to be stocked. 

 For ponds and lakes in England and the south of Scotland, it is 

 desirable to introduce fry hatched from the ova of the oldest and 

 largest parents. The same rule applies to large rivers, as the 

 Thames below Oxford, and generally to all sluggish streams in 

 the south and midland portion of England. On the other hand, 

 when a small cold mountain stream is to be stocked, or a hill 

 lake, where the chief advantage must arise from the introduction 

 of fresh blood, fry from the ova of four-year-old fish should be 

 selected. Between these extremes lies a vast and, as yet, little- 

 trodden field of scientific pisciculture, it is therefore of great 



