Aethue. — On Pish Culture in New Zealand. 207 



Hatching the ova. — In these boxes, as just described, the impregnated ova 

 are carefully put and distributed all over the gravel in a single layer, wooden 

 covers being then put upon the top of each box. Wide-mouthed bottles 

 drop in the ova well. Notwithstanding all care, there is always more or less 

 of a deposit from the water on the eggs, particularly at the lower ends of 

 the boxes (see note in appendix). This, however, we have never found 

 injurious, though it is objectionable. It can be removed by a camel hair 

 brush, moving the water with a spoon, or increasing the flow of water, the 

 latter being a cure to be avoided if possible. I may here mention in passing, 

 that Mr. Frank Buckland made some experiments to ascertain what weight 

 would be required to crush the eggs of the salmon, when he found it to 

 be 51bs. 6ozs. I have not tried what trout eggs will bear, they are con- 

 siderably smaller than those of salmon of equal weight, but that fact does 

 not indicate lesser strength, and it is very probable that they are as strong 

 as those of the nobler fish. This astonishing strength seems to be a wise 

 provision of nature, as in the natural ridds the ova of both these fish are 

 liable to rough treatment and great pressure from superincumbent gravel. 



The period of incubation, if I may use the expression, is found at the 

 Opoho ponds to average 78 to 88 days under ordinary conditions of weather, 

 and the time from impregnation till the eyes of the fish appear, 45 to 50 

 days. A difference in the temperature of the water of 1|- degrees is found 

 to make a difference of 10 days in the time of hatching. The average 

 temperatm'e ranges from 42° to 52°, but the strongest and healthiest trout 

 hatch out in water at 48°. The period of hatching is from 8 to 14 days, 

 that is between the first and the last trout breaking out of the egg. The 

 umbiUcal bag in the young trout hatched in September and October, 1880, 

 took from 50 to 56 days before it was entirely absorbed. From the time of 

 the sac being absorbed the fry are fed with grated raw liver until liberated, 

 the sac being supposed to contain all necessary nourishment up to the time 

 of its disappearance. In Yarrell's " British Fishes," p. 269, experiments 

 in trout rearing in Germany are referred to, where the time from impregna- 

 tion to the eye appearing was 21 days, to the hatching out of the fish five 

 weeks or 35 days ; and from hatching out to the absorption of the umbilical 

 sac three or four weeks or 28 days. Thus it would appear that the trout 

 reared at the Opoho ponds take as nearly as possible twice as long as fish 

 in Germany to pass through the same stages from impregnation to absorp- 

 tion of the bag. Some tables at the end of this paper may be found useful, 

 giving a few details of temperature and hatching out in Otago. The 1879 

 fish grew much quicker than those of 1880, which were remarkably backward. 



The young trout. — After hatching, the young trout (as stated above) are 

 fed with grated raw liver, and this food is continued to them for some time 

 after. They thrive very well on it, and feed, as we believe, on small water 



