_ 17 — JOH.HJORT AND C. G. JOH. PETERSEN 



men state where the marked fish have heen recaiight, it is possible to determine, in addition 

 to their rate of growth, also their wanderings during the time which has elapsed, and 

 to gain in this way good information concerning the biology of the plaice, which would 

 otherwise be difficult to obtain. It has also resulted from these marking experiments that the 

 number of marked fish returned is extraordiuarily great; thus, the Danish experiments have 

 shown, that 43.4 "/o out of 1099 Jplaice set out in the North Sea have heen recaught within 

 14 months, 58.5% out of 121 plaice marked in the Skager Eak were recaught within the 

 same period, and in the northern Kattegat even 80 "/o of the marked plaice have been returned 

 within 4 months. In addition, it has to be noted that a portion of the fish recaught are in 

 various ways lost, i. e. not returned. Through these high percentages, one gains a good notion 

 of the intensity of the plaice fishery in the North Sea and Danish waters. 



The marking-method has also been used for other species as well as the plaice, e. g. for 

 the cod and eel, and it will assuredly prove to be practicable, with certain modifications, for 

 various other species of fish. 



It is indeed of the greatest interest to be able to determine how far the migrations of 

 the fishes extend, and if we could also learn fixed recognition-marks for the fishes from 

 different waters, this would have an extraordinary importance. The scientist who has first 

 begun such race-investigations on fishes, is Fr. Heincke. His race-investigations, 

 based on measurements, number of vertebrae and so on, are well known. For other species 

 also, the number of the vertebrae and fin-rays seem to have great importance. Thus, we know 

 that the plaice of the Belts have a smaller number of fin-rays than those of the North Sea 

 and the Skager Eak. From such race-investigations, carried out on dead material, various 

 conclusions can already be made; but the inheritance and constancy (fixity) of the characters 

 cannot be determined in this way. Purely experimental attempts at rearing the young fish, 

 such as are in the program of Committee C 2, are necessary in order to solve such questions. 



B. Examples of the results obtained 



. 1. Eggs, larvae and young fishes 



The economically important fishes can be divided, as regards their natural history, into two groups : 



fish, with floating pelagic eggs, 



fish, which lay their eggs, demersally, on the bottom. 



The eggs of the first group develop, and their larvae hatch out, whilst floating in the water; those 

 of the second group, on the other hand, carry through their development on the bottom. The 

 small larvae which come from the eggs are pelagic in both groups, the duration of the pelagic 

 stage is however, different for almost every species. In some species the larvae seek the bottom, 

 in others the larvae remain pelagic during their change to young fishes, even much longer in 

 some cases. As the first pelagic stages are in the highest degree dependent on the movements 

 of the surrounding water, an exact investigation of this period of life has great importance for 

 understanding the fate of the eggs and larvae, and also, the distribution of the later, first bottom- 

 stages. For this reason, specially great attention has been devoted to these .investigations, and 

 this had the practical advantage also, that it was easier to find the free-floating eggs, larvae 

 and young fishes with pelagic nets than the demersal eggs on the bottom with di-edges and trawls. 



Appendix G- 3 



