The method of Rravel-bed hatching is popular again in the Rhine and Moselle regions 

 in Germany, also in Holland. Trout, and above all salmon, are hatched in this way. The 

 method was widely discussed in Germany, at the turn of the Century as the method nearest 

 to natural salmonide hatching conditions. Alternating layers of gravel — 2 to ^ centi- 

 meters thick — and of freshly fertilized salmonoid eg^.'S were than put into large "long 

 stream" troughs of either wood or cement. The gravel had to be coarse enough so as not 

 to press upon the eggs, filling the spaces between the gravel and allow for a free play 

 of the water. The resulting brood is unusually strong and healthy but the losses of 

 eggs are relatively higher than in other methods. The gravel beds remain completely 

 undisturbed until the brood begins to feed. They are than removed by means of hands or 

 of dull forks from the troughs. One advantage of this method is that bad eggs have not 

 to be sorted out. 



At the hatchery of the monasterj"- of Maria Laach, I came across a somewhat peculiar 

 hatching apparatus. It was a closet-like contraption with doors, designed to darken the 

 incubator. In the Harz mountains, I found large, water- filled wooden boxes. Here, the 

 eggs were hatched upon layers of stone splinters, sprinkled with water from a fountain- 

 like contraption. 



The most simple of all hatching apparatus is the "hatching pot" and vrtiich is practical- 

 ly nothing but a stew pot or sauce pan full of holes and which, when filled with eggs is 

 simply set into a brook or into a wooden pipe with running water. All of these "incubators" 

 are of course designed for "home use" only, and have no place in industrial plants, nor are 

 they to be compared with any modem apparatus. 



Eggs of marane, pike and many other fish cannot, on account of their small sizes, be 

 hatched in trout incubators. From my own experiments, I recommend for them such apparatus 

 as the so-called "Zuger glass" sind the "von dem Borne" apparatus made of tin. 



The "Zuger glass" (to be had at Bartsch, Philipps & Co., Berlin NW UO, Doberitz Strasse 

 3, or at the Ver. Lausitzer Glasswerken A. G., Berlin SO 36, Lausitzer StrasselO) consists 

 ■of a glass cylinder with a funnel-shaped opening at the bottom. It is from 50 to 65 centi- 

 meters high and contains from 5 to 9 liters. The glass is fastened to a small white metal 

 box (see Fig. 27). 



The difference between the water level of the conduct pipe and the upper rim of the 

 glass — the so-called pressure — is best 1 meter. A conduct pipe with an inflow opening 

 into the glass of 9 millimeters will provide for a through current of from 0.07 to 0,1 

 liter per second, which is sufficient for all practical purposes. 



The whole pressure, that is, distance from conduct pipe to bottcxn of the box is there- 

 fore about 1.80 meter. By lack of pressure, I recommend the "von dem Borne" apparatus and 

 which has given as good results as the "Zuger glass" at our hatchery at Eberswalde. Also 

 the idea, underlying the "Macdonald glass" is practical from the fishbreeder's viewpoint. 

 I must also recanmend that larger establishments seek the advice of specialist fishery 

 biologists to conform with local conditions. 



The above named apparatus are filled to not more tten half with freshly fertilized 

 eggs. The brood is caught in especially constructed white metal boxes which are placed 

 under the outflow opening of the "Zuger glass" (see Fig. 27). These boxes are best 

 covered with a soldered-in screen of finest hair sieve in order to avoid an escape of 

 the very small broodlings. 



The incubator may be installed outside (see Fig, 28) or still better in a hatch house 

 or hatch rocm, A cellar, or a wing at least half sunken in the groimd (see Fig. 29), or a 

 special small house may be used. Most important in every case is the level trough (Fig, 28) 

 made of wood, strong tin or masonry, through which water runs continuously and flows out 

 through an overflow. The incubator apparatuses oa bucks or similar supports are placed 

 under the faucets connected to the level trough or are connected to the faucets by means 

 of pipes and hoses (Zuger Glasses, see Fig. 27). In recent, more wastefully constructed 

 incubator houses, the long-stream apparatuses are often firmly set in masonry. In every 

 case, care should be taken that the outflow water does not run on the floor of the 

 incubation room, but through special outflow channels. 



112 



