1 62 How to obtain it. 



Take care to keep everything very clean, therefore; keep the 

 boxes covered, and have all the woodwork well varnished, and 

 there is little to fear from this enemy. 



Sediment is also a danger which should be carefully guarded 

 against. Unless great care be taken it is sure to come, and to 

 settle more or less upon the ova. Although I have known cases 

 in which sediment has apparently had no very prejudicial effect 

 upon ova, yet other cases have come under my notice in which 

 very serious harm has accrued. At some periods of their existence 

 eggs would not be so much affected by it as at others, and the 

 sediment itself varies very much according to circumstances. In 

 some waters it would be almost entirely mineral, whilst in others 

 it would be chiefly of a vegetable or organic nature. Or it might 

 consist of both mineral and vegetable matter. Some deposits are 

 directly poisonous, as for instance in cases where copper or lead 

 are present. Others again are highly injurious, as for instance 

 iron or lime, although I have seen good work done in water 

 containing both. But assuming that a sediment could deposit on 

 the eggs, of such a nature as to be quite innocuous in itself, the 

 result must tend towards suffocation. This may be only partial 

 but, nevertheless, it is sufficient to arrest the development of the 

 embryo, and as a consequence deformities are produced. It is 

 well known that the ova of salmonoids require a good supply of 

 oxygen. They likewise give off carbon, in the form of CO 2 , which 

 requires to be carried away from the eggs as produced, and when 

 covered with sediment this healthy change of condition is not 

 maintained, and should it remain long enough many of the eggs 

 will be poisoned. Although they may be not absolutely killed at 

 the time, the result will probably be weakly or deformed fish. 



When eggs are packed in moss and sent long distances 

 cripples usually occur in excess amongst the fry produced. This 

 has been notably the case amongst eggs imported from abroad. 

 It is not at all surprising that this should be so when the develop- 

 ment of the embryo is considered. The pressure, slight as it may 

 be, of the layers of moss upon the eggs, is quite enough to cause 

 the many curved spines and other deformities, that occur under 

 such conditions. Concussion has also been found to produce a 

 similar effect, and often to cause the death of the embryo. 



