532 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 



cover the gravel one or two inches deep. In tbe use of several troughs 

 he x^rovides for a main pipe, conducted across the head of the troughs, 

 with outflows into each. "This done, you have all the apparatus neces- 

 sary for breeding trout and salmon." 



Jacobi understood that only a small quantity of the milt was necessary, 

 because it contained vast numbers of the spermatozoa, and would fertilize 

 a large number of eggs. 



His manipulation of the male and female trout, stirring the milt 

 through the eggs, and the addition of fresh water after impregnation of 

 the eggs, is very similar to modern practice. The necessity of sepa- 

 rating the eggs in the troughs was well understood, though, instead of 

 a feather, he, by means of a thin paddl<^ of wood, produced an eddy iu 

 the water that spread the eggs over a larger surface. The fine, downy 

 fringe of the conferva growth was a difficulty he had to contend with 

 as well as modern workers iu the art, and the little trout of ancient 

 times had the same tendency to hide themselves in the gravel when 

 young that they do at this day. 



His gratings did not prevent the egress of the young fishes, and he 

 provided them with nurseries at the end of the troughs. Monstrosities, 

 iu the shape of double-headers, he seems to have been familiar with, and 

 found them short-lived. 



Jacobi seems to have been a man of intelligence and application. 

 Some of his conclusions, however, have since been entirely disproveu 

 by investigators in embryology. 



The progress made iu the methods and' apparatus of fish culture has 

 been very great, as the result of the experience of many experts, and 

 in certain lines is entirely new and novel ; but the present graveled 

 trough method for hatching trout and salmon is only an improved 

 modification of the boxes and troughs used by Dom Pinchon and Jacobi. 



The necessity of filtering the water through screens, the advantage 

 aftorded by dividing the troughs into nests, by means of cleats, so that 

 the bed of gravel may be kept level, and i^revent the tendency of the 

 eggs to collect iu heaps, the shutting out of light from the eggs, the 

 immense reduction of loss from the removal of dead eggs and fungus 

 growth, the transportation of partly-developed eggs, and feeding young 

 fish with prepared food, were all entirely unknown to the earlier authors; 

 as also the numerous improvements in the mauipulations, the guard- 

 ing against the ills incident to the eggs and young fishes, that have 

 grown up in the experiences of the numerous workers in the art. Jacobi, 

 indeed, does not seem to have carried forward his discovery to any ex- 

 tensive practical result, although an establishment at Nortelem was 

 sustained for a short time, and the English government had sufficient 

 appreciation of his work to afford him a pension. 



xldanson, in a course of lectures delivered in Paris in 1772, made the 

 statement to his. auditors that the art of fish culture was prosecuted 

 with success on the river Weser, in the Palatinate of the Ehine, and iu 

 some of the higher mountainous portions of Germany. 



