42 U. S. BUEEAU OF FISHERIES. 



is reached, then with the thumb and the index finger the abdomen is 

 pressed gently, and at the same time the hand is slipped toward the 

 vent. If the eggs are ready to be taken, they will come freely and 

 easily. If they do not come freely after the first pressure, the hand 

 is moved toward the head of the fish and a very gentle pressure is 

 applied to assist the natural flow of eggs until all that will come 

 readily are obtained. Pressure should never be applied forward 

 of the ventral fin, as even slight pressure over the vital organs is 

 very apt to result in injury. 



By this method all of the eggs that have fallen from the ovaries 

 and are ready to be expressed will fall into the abdomen near the 

 vent, so that it will not be necessary to press the fish again over its 

 vital parts, the eggs having left that portion of the body. An ex- 

 perienced operator can tell almost at a glance whether or not a fish 

 is in spawning condition as soon as it is lifted from the water. By 

 grasping the fish as described, holding the head highest, if ripe eggs 

 are in the ovaries they may be observed to roll slightly toward the 

 vent. If this movement can not be detected, the right hand may be 

 passed lightly down the abdomen, and if the egg mass is soft and 

 yielding to the light touch the eggs will flow freely from the vent 

 with but slight pressure. Examination of a large number of speci- 

 mens has proven beyond doubt that serious injury, resulting in 

 barrenness or death, is very likely to result from improper handling 

 of fish at spawning time. 



Eecent studies^ tend to correct the long accepted belief that the 

 mature eggs of trout and certain other salmonoid fishes fall loosely 

 into the abdominal cavity and from there are extruded. As a matter 

 of fact the ovaries of the Salmonidse are inclosed in a delicate mem- 

 brane, and the eggs are conveyed to the genital pore through an open 

 membranous trough. The ova do not fall naturally into the abdomi- 

 nal cavity, and it seems probable that they can not be extruded if they 

 are inadvertently displaced into it, and their presence there can not be 

 advantageous to the fish. 



Careless fish-cultural methods are responsible for displacing the 

 eggs. Some of these are dipping the fish head first into a dip net, 

 causing it to flop about, and grasping the fish by the tail and holding 

 its head until its struggles cease. The dip net should always be 

 large enough to permit the fish to lie extended. If the fish is ripe or 

 jDartly ripe, the mass of eggs may be seen to sag toward the head, 

 and inevitably any free eggs settle in the forward end of the ab- 

 dominal cavity outside of the ova-containing membrane. It is after 

 the stripping process has begun, however, that the danger of displace- 

 ment is greatest, and particularly after some eggs have been ex- 

 pressed and the tenseness of the supporting abdominal wall is re- 

 laxed. Displacement is largely responsible for failure to secure all 

 of the ripe eggs, and even though the fish may emit retained eggs 

 later it is impossible for it to rid itself of displaced eggs. 



Another disadvantage from which the fish may suffer is rupture of 

 the membranes and injury to the ovaries from forcible pressure, so 

 that the eggs falling into the abdominal cavity are not secured. 



Peritoneal Membranes, Ovaries, and Oviducts of Salmonoid Fishes and Their Signifi- 

 cance in Fish-cultural Practices. By William Converse Kendall. Bulletin U. S. Bureau 

 of Fisheries, Vol. XXXVIII, 1919-20. Bureau of Fisheries Document No. 901. Some 

 Previously Unrecogniaed Anatomical Facts and Their Relation to Fish-cultural Practices. 

 By William Converse Kendall. Transactions, American Fisheries Society, 1920. 



