APPENDIX a _ 16 — 



necessary to hatch out the living fish-eggs on board the investigation-vessels, in order to follow 

 the development etc. of the fish quite from the egg onwards, hy means of these young and by 

 series of older stages. Ehrenbaum has contributed much to our knowledge of the coast- 

 fishes of the southern North Sea in a work recently published. Williamson in Scotland 

 has described a series of stages of Pleuronectes cynoglossus. Petersen in the Meddelelser 

 fra Kommissionen for Havundersegelser, Bd. I, has represented a series of stages both of this 

 fish and of two other species of Pleuronectes, and his investigations over the remainiug Pleuro- 

 nectidse are to be expected in the near future. Jobs. Schmidt has undertaken the inves- 

 tigations of the gadoid species. The preliminary investigations are thus making good progress. 



A method which has already been employed for many years in the service of the fishery 

 investigations, especially by Petersen for the Danish waters, is the method of measurement. 

 If a quantity of fish of any species has been taken, it often happens, on measuring and 

 arranging these fish one after the other, according to a plan like the subjoined (PI. IV) showing 

 the cod from east Iceland, that they form various groups according to size, i. e. that 

 certain lengths are represented by far more fish than others, for example 5, 12, 22, 33, 61, 

 68 cm. in the subjoined plan. In this plan therefore, there are 6 such lengths. With other 

 fishes, e. g. several of the Pleuronectidse, a different number of groups appears, and at other 

 places, e. g_ Denmark, different groups are found for the cod than those given. Investigations 

 concerning the appearance of such groups at different periods of the year, have now shown that 

 they signify the yearly growth of the fish as a rule. It must be remembered that, in a given 

 region, all cod usually spawn together at the same time of year and not in equal portions 

 throughout the year. It wUl be understood therefore, why the young of the different yeai'S is 

 of such different sizes in the plan, and that, from such a measurement of a very large number 

 of fishes of all sizes occurring in a region, we can obtain an impression of how quickly the 

 fish grow on the average. This method is at present in use almost everywhere, where thorough 

 investigations are being made, and it has appeared from these, that the fishes grow very differ- 

 ently under different conditions. As the method is so generally used we shall not dwell 

 further upon it, but mention only that it can give a view over the rate of growth and age of 

 fishes only in general; the age of the individual can often not be determined by it. This want 

 in connection with, the measurement-method seems in part to be helped out by other methods 

 for the age-determination of the fishes, namely, by investigation of the otoliths (ear-stones) ; 

 these investigations have been carried out by German scientists especially. Possibly the inves- 

 tigation of the bones will also give information concerning the age; too little has as yet 

 appeared, however, for one to be able to judge concerning this method. 



Quite a different method of obtaining information concerning the rate of growth and 

 migration of fishes is that of marking living fishes. This method has been brought into 

 use, chiefly by the Danish biological station, and has led to extraordinarily great results so far 

 as the plaice is concerned. To the living fish two bone-buttons are attached, which are held 

 in position by a silver wire and a number is burnt on one of the buttons. It has been 

 shown that fish marked in such a manner can live and gTOW. When a number of fish thus 

 marked were set out in Danish waters, a portion of them have been caught again and 

 sent in by the Danish fishermen within a short time; the same thing has happened in the 

 North Sea, where many thousands of plaice have been set out of recent years. If the fisher- 



