LIFE HISTORIES OF CERTAIN' FRESH- WATER FISHES. 479 
are deposited singly and they are smooth and non-adhesive, 
being buried amongst the gravel in clear water. 
The period between the fertilisation of the egg and the 
hatching of the larva varies considerably among the fresh- 
water fishes ; the eggs of the Pike for instance hatch in about 
10 or 12 days whereas those of the Trout or Salmon take from 
80 to 100 days, and even longer before hatching. The con- 
dition of the larva when hatched also varies considerably. 
The Trout or Salmon hatches out as a highly pigmented 
opaque alevin with a large yellow or orange yolk sac attached 
to it, while the Perch hatches out as a transparent larva 
invisible but for two large dark eyes. Thus there is consider- 
able variety in the early stages of fresh-water fishes, the 
various differences being associated with differences in habit. 
Coming now to the particular species which I have had the 
opportunity of observing : — 
The Pike ( Esox Indus), according to authorities, breeds in 
March and April, sometimes as early as February. The 
earliest record which I obtained at Sutton was March 14th, 
1903, when I obtained a small ripe female fish. On several 
occasions 1 obtained ripe male and female fish at the same 
time and fertilised the eggs by what is called the dry process 
in Salmon and Trout culture. The eggs were expressed from 
the female fish into a dry basin and the milt from the male 
was expressed over them — water was then added, and the 
whole thoroughly shaken up. In the meanwhile most of the 
eggs had adhered to the basin and after being allowed to 
remain for a few minutes the water was poured off and fresh 
water added, the eggs being thoroughly rinsed. They were 
then gently removed one by one from the basin and allowed 
to sink on to water plants, to which they at once adhered, 
in the aquaria where they were to develop. 
The egg of the Pike is large and easily recognised. It 
measures about 3.0 mm. in diameter, and is of a pale yellowish 
colour and contains scattered groups of minute oil-globules, 
giving it some resemblance to the egg of the common Sole 
(Solea vulgaris). 
About the 10th day after fertilisation the eggs hatch, the 
opaque yellowish larvae from 7.0 to 9.0 mm. in length, being 
