_ 7 — APPENDIX E: HEINCEE 



whatsoever, which can give us any trustworthy information regarding the fish-population 

 of such grounds. The line- fishery is often the only means available here and it is 

 a very untrustworthy method. It unfortunately yields no information whatsoever regarding 

 the younger stages of the fishes. 



Although all these things are tolerably well-known, as a matter of fact, or should be 

 known, they must always be repeated again, and they require the greatest consideration 

 when it is a question of scientific fishery experiments and of the estimation of their results 

 for wide-reaching conclusions, or for the formation of theories regarding the migrations of 

 the food-fishes etc. We are of the opinion that very many wrong inferejices have hitherto 

 been made in this connection. Above all, it is necessary to strongly guard 

 against drawing wide-reaching conclusions from negative results in scien- 

 tific fishery experiments, and against building any hypothesis on them. On 

 account of the undeveloped condition in which our technique of the scientific fishery is at 

 the present time, it is, for example, practically never possible to conclude that no young 

 plaice or young cod in their first year occur in this or that spot, because no one has as 

 yet found them there. Only in single, quite few and quite special cases have we a certain 

 right to make such a conclusion. 



On the other hand, the proof furnished by a positive observation is 

 incontestable. We rely — especially in this account of our results — only on them. 



Positive results, however, have only sufficient value for further conclusions, when it 

 is possible to distinguish with perfect certainty the captured eggs, larvae and early young 

 stages of food-fishes according to their true species. The difficulties here have also been 

 greater than desirable, hitherto. 



For example, the eggs of two of our principal food-fishes, the cod and haddock, are 

 not always to be distinguished from one another in the early stages of their embryonic 

 development, and this holds also for the larvae of some nearly related flat-fishes, especially 

 when the pigment characteristic for the species is lost in preserving. Our observations 

 have shown, that very many erroneous determinations are contained in earlier works on the 

 larvae and young forms of the food-fishes. 



The exact separation of the various age-groups of the food-fishes has 

 proved to be quite an indispensable, though very difficult work. The methods used 

 hitherto, of measuring the numerous fishes of a catch and then of distinguishing the age- 

 groups by the maxima and minima of the curve constructed from the measurements, has 

 turned out to be very untrustworthy in most cases , and given rise to many wrong con- 

 clusions. The discovery of Reibisch of Kiel, that the layers in the otoliths of fishes 

 showed the periodic, that is, the yearly growth of the fishes, has first displayed the possi- 

 bility of a true and exact determination of the age. We have devoted special attention to 

 this matter and applied the investigations of Reibish on the otoliths, to many thousands 

 of fishes. At the same time, similar signs of periodic growth have been found on numer- 

 ous other parts of the bony skeleton of fishes, and closely studied. We believe we are in 

 the position to record a number of positive and certain results from this work. 



