40 XT. S. BUREAU OP FISHERIES. 



The work of preparing the nest is performed chiefly by the male 

 fish ; upon completion the male and the female enter it together and 

 by a rolling spasmodic tremor they deposit eggs and milt, which are 

 brought together and mixed by agitation of the water. For a short 

 period after they have been deposited the eggs are slightly adhesive, 

 and during this time they absorb the impregnated water. Wlien 

 filled they fall apart and settle down between the gravel and stones 

 of the nest, where they lie protected until hatched. 



Under domestication the fish rarely will deposit their eggs of their 

 own accord unless conditions are favorable. Swift, well-aerated 

 water of suitable temperature, gravelly bottom, and a male consort 

 seem to be necessary, although instances have been recorded where 

 female rainbow trout have deposited their eggs on the cement bot- 

 tom of the stock pond without a male fish in attendance. On the 

 other hand, adult fish in an aquarium have been observed to make 

 nests and apj)arently attempt to spawn, failing in the efi'ort and later 

 dying with the eggs still retained. Instances have been reported, 

 also, where fish (rainbow trout and landlocked salmon) have been 

 taken from native waters several months after the spawning season, 

 apparently still retaining their full quota of eggs in the ovaries. In 

 every case the eggs were hard and " glassy," though as far as could 

 be observed the fish had suffered no ill-effects as a result of their 

 unnatural condition. Under any circumstances, however, retention 

 of the eggs beyond the spawning period is, of course, unnatural and 

 undesirable. In practical fish-cultural operations easy access to a 

 suitable spawning race will invariably permit the fish to spawn or 

 to indicate that they are ready to spawn. Overlong retention of 

 eggs undoubtedly results in " glassy " eggs, probably caused by their 

 coming in contact with a serious ovarian exudation present in the 

 fish under these conditions, and may also result in serious permanent 

 injury or even death to the fish. Eggs that absorb this fluid become 

 hard and incapable of fecundation. Similarly, freshly extruded eggs 

 if immersed in water which lacks the male element of fecundation for 

 even a short period become hard and " glassy." 



Wlien spawning ponds are provided with suitable raceways, the 

 fish will ascend from the ponds into them in search of a place to 

 nest and may then be taken out and stripped of their spawn. To re- 

 move the fish from the raceway, a square net {B^ fig. 11) is dropped 

 in on cleats bolted against the side walls in the approach, the dam 

 in the mouth of the raceway is raised, and the fish driven back 

 into the net. The net is then lifted out of the water, and if it con- 

 tains too many fish to handle conveniently a landing net is used to 

 take out part of them before the square net is moved. The ripe fish 

 are then placed in tubs or other vessels provided for the purpose, but 

 care should be taken not to put too many in the tub at one time, as 

 they will become restless or sick before they can be stripped of their 

 spawn. While being held in this way the water in the vessel should 

 be renewed frequently. 



There are two methods of taking and impregnating the spawn of 

 fishes — the " wet " and the " dry " methods. By the wet method 

 the eggs are taken in a pan containing sufficient water to cover them 

 and allow them to mix freely with the milt, which is added imme- 

 diately. After the contents of the pan has been stirred for a few 



