fish is more endowed with these qualities than its retarded mates. Many trout in the 

 Baltic Sea were finally Just as much retarded in their growth as pond fish. Selective 

 breeding must for eyer remain the most important factor in trout culture . As a matter of 

 fact, one finds today in German trout fisheries especially well performing "breeds" of 

 broodstock obtained through selective breeding and which may well be spoken of as "races". 



I wish to mention here that the variety question played a certain role in the import- 

 ation of rainbow trout from America. Originally, these importations were designed to com- 

 bat certain symptons of degeneration through the introduction of fresh blood. Such symptoms 

 of degeneration are closely interwoven with the problem of race development. In themselves 

 they do not represent anything homogeneous. Probable causes for degeneration may bes 



(1) Genotypical factors, inbreeding for instance^- facilitate the reappearance 

 of recessive and undesirable hereditary characteristics, 



(2) Paratypical factors, to which belong bad care, improper food and feeding, 

 etc., that is, bad management. 



It is obvious that the ravages enumerated under 2 can be avoided. Their prevention 

 is the most important means to avoid degenerative symptoms altogether. Inbreeding does 

 hardly any harm in trout culture, since the number of offspring is really enormous. And 

 according to the laws of heredity, only a small proportion (up to 1/4) can be afflicted 

 with undesirable, recessive characteristics. Such fish are easily eliminated or eliminate 

 themselves. The loss on the basis of enormous quantity of progeny is really not great, 

 since young fingerlings, altogether, are of little commercial value. 



The large number of offspring makes speedy development of favorable hereditary factor 

 combinations possible and at the same time facilitates the elimination of badly endowed 

 individuals from the field of reproduction, and precisely by means of inbreeding. 



Inbreeding in fish culture is therefore of really positive value, as is shown by 

 well managed fisheries. 



The great advantage of a numerous progeny has, on the other hand the disadvantage 

 that fish mature relatively late. The number of fish generations within a certain space 

 of time is smaller than in domestic animals. 



Ehrenbaum has rightly emphasized that degeneration or degenerative syii5)toms, caused 

 through inbreeding are negligible in trout culture. In America such symptoms occur at 

 all times, the steady supply of fresh blood notwithstanding. 



Nothing special needs to be said regarding the supply of spawners of other kinds of 

 fish such as salmon, graylings, maranes and pike for artificial culture. As a rule they 

 are stripped immediately after they are caught. Pike and also maranes must not be stored 

 for any length of time, because the sex products repidly become unusable. Tomuschat, to 

 be sure, announces good storage results with small maranes. With maranes, but particularly 

 with pike, the use of a relatively larger number of males (which mostly ripen before the 

 females) is advisable to insure fertilization. Here the possibility of obtaining artific- 

 ial brood depends upon the simultaneous catch of ample amounts of fully ripe milters and 

 spawners. 



3. Artificial Extraction of the Sex Products . 



We distinguish between "wet" and "dry" fertilization. In "wet" fertilization, roe 

 and milt are stripped from the fishes right into the water. By using the "dry" method, 

 water is added only after the stripped sex products have been thoroughly mixed. "Dry" 

 stripping is based upon the observation that milt, so stripped, remains fertile for a 

 number of dajrs, while the resulting motility from the addition of water lasts only a 

 short Willie. (According to Scheuring, 1928, milt from rainbow trout — at a temperatxire of 

 from 4. to 8 degrees centigrades — remains usable for ten days, milt fron brook trout for 

 only one to two days and the not stripped milt in dead fish only from 12 to 2U hours. 



106 '-T»W 



