498 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [8] 
to cover the bed with a thick layer of stones, gravel, and sand, so as to 
induce the females to come and hide their eggs there. 
These measures cannot in all cases replace artificial fecundation unless 
there is no danger of the spawn being destroyed in its free condition, 
and thus there is no ground for the objections Peay against the natur al 
restocking of our rivers. 
§ 5.—Crossing of different breeds. 
It rarely occurs in nature that different breeds of fish will cross,* 
which is easily explained by the circumstance that the milt soon loses 
its fecundating property. Guided by their instinct the male fish de- 
posit their milt in close proximity to the eggs laid by the females of 
their kind. The short duration of the fecundating faculty of the sperm- 
atozoa, when brought in contact with the water, does not allow the 
milt to attach itself to other eggs than those for which it is destined. 
The possibility of producing cross-breeds is beyond a doubt. Thus 
at Hiiningen a cross-breed has been obtained from the common trout 
and the salmon, from the salmon-trout and salmon, and vice versa. <At- 
tempts made in Bavaria to cross the trout and the pike have not proved 
successful, whilst the crossing of the common trout and the blay (there- 
fore two different families) was successfully accomplished.t Cross- 
breeds have been produced from different species of trout among them- 
selves, and specimens of these crosses are found in large numbers in 
the fish-ponds of the veterinary school at Munich. In crossing differ- 
ent breeds of fish, especially salmon, the object is to obtain fish able to 
live in those shallower waters in which those among them which live 
near the bottom of the lakes do not prosper. 
We only mention these facts briefly, as our experience so far does 
not justify us in passing a final verdict as to their absolute reliabil- 
ity, and as to the profit which might be derived from crossing different 
kinds of fish. We have very good reasons for this; the majority of 
these cross-breeds are deprived of the faculty of reproduction, and if 
this is not the case they gradually return to their original types. The 
alleged fact of the sterility of certain cross-breeds is beyond a doubt; 
it is proven by the hybrid products of various kinds of salmonoids often 
met with. These cross-breeds, in which Dr. Fraas of Munich invari- 
ably found only a few sickly-looking eggs, can never spawn. But there 
are cross-breeds which can do it, as the cross between the carp and 
the crucian. Future experiments must show what are the species be- 
tween which a cross can be effected and the conditions under which 
this can be done successfully. The objections raised against the pro- 
duction of cross-breeds is well founded, and in order to overcome it 
* We occasionally meet with a cross-breed of the crucian and the common carp, and 
of the latter with the Chinese gold-fish. These cross-breeds may be recognized by 
having smaller scales and a shorter and thicker head. 
- +Dr. FraAas: Die kiinstliche Fischerzeugung, p. 57. 
