17 



The occurrence of the pelagic youug of various species having peiagic 

 eggs will be described in more detail in the special part, but only for those species, 

 whose development and distribution in the various stages we have learnt to kuow 

 best during our investigations, namely: cod, whiting, plaice, fiounder, dab aud 

 long-rough dab, as also the two gadoids: haddock aud Norway pout, the distribu- 

 tion of which in tlie pelagic stages is specially iuteresting, 



Pelagic young from species with deiuersal eggs. 



The fish youDg hithei'to mentioned are all hatclied from pelagic eggs; but 

 a large uumber of youug oceur in Danish waters, which come from species with 

 eggs fixed to the bottom or to its plant-vegetation (the eggs are therefore called 

 demersal). 



The conditions of distribution for these young are much less complieated 

 than for those which come from pelagic egjgs, because the fixed eggs do not come 

 under the influence of curreuts; and it is ouly when the young are hatched that 

 they go with the stream. The young of fish with demersal eggs are tlierefore most 

 frequent in the neighbourhood of the coast, and appear in much greater numbers 

 iu the smaller waters than in the Skager Rak and North Sea. This is seen in 

 our catches for 1904 for example. The summary of these (Tab. 3 B) shows, in 

 the column for the young of species with demersal eggs, that the greatest numbers 

 are always fouud in the inner waters, including the Kattegat, whilst the North Sea 

 and Skager Rak are represented by small catches. 



Amongst the young of fishes with demersal eggs are some species, which 

 appear pelagically in winter and spring, whilst other species pass though their 

 pelagic stages in the warm period of the year. The great majority of the species 

 beloug to the latter class, but richness in numbers is not in proportion to the 

 numbers of species, as many of the youug hatched from demersal eggs in the 

 course of the summer pass the whole of their early life near the bottom amongst 

 the plant- vegetation, often in shallow-water. It is only exceptionally that they are 

 met with free in the water and are taken in the hauls in iutermediate layers, and 

 it is only such cases that are brought iuto the lists amongst the pelagic young. 



The earliest pelagic young of fishes with demersal eggs may be divided 

 iuto two main groups: the cottoids aud the "elongated larvæ". The eottoids are 

 represented by the common sea-scoypion (Cottus scorpius) and the ^jo^rr/e (Agomis 

 cataphractus). Both these species are very common in the first nionths of the 

 year; they will be mentioned more particularly in the description of the species. 

 Amongst the "elongated larvæ", the herring and sprat (Clupea sp.), Luvipenus 

 (Lumpenus lampetriformis), gunnel (Centronofns gtmellus) and sandeels (Ammodytes 

 sp.) are the most frequent. A key to the determination of these is given by the 

 Director in "De danske Farvandes Plankton" I, p. 246 — 247. Amongst the elongated 

 larvæ must also be reckoned the pelagic young of the crested bleuny (CarelopJws 

 ascanii) and cat-fish (Anarrhichas lupus), which belong to the rarer visitors in 

 Danish waters. Like the cottoids the "elongated larvæ" are most abundaut in the 

 first mouths of the year. They decrease in number in April — May aud quite 



3 



