of the Fishery Board for Scotland. 



ii 



from the sea, and had consequently passed some time (estimated at 

 about two months) in the river. The value of Professor Meischer 

 Ruesch's paper,* which in other respects is probably one of the most 

 valuable contributions hitherto published on the life-history of the salmon, 

 is somewhat impaired owing to the fact that he does not appear to have 

 possessed sufficient data as to the condition of salmon taken in, or just 

 after leaving, the sea. This want has been supplied by Dr Hoek,f 

 Scientific Adviser on fisheries to the Dutch Government, who may be said 

 to have completed these investigations by examining a large number of 

 salmon taken in Holland. 



As a means of comparing the rate of growth of the sexual organs at R ate o( - o rmv th 

 different periods throughout the year, these observers calculated the propor- of sexual 

 tion of the weight of these organs to the weight of the body of the fish. or g ans - 

 Professor Meischer Ruesch further studied their growth and progress of 

 development by the help of the microscope. Dr Hoek is of opinion that 

 these proportions, which he averaged over ten-day periods, show clearly 

 that their development advances with great regularity. He points out that, 

 although the differences are at first small and almost insignificant, it can 

 hardly be accidental that, considering the very large number of observations 

 from which the averages are computed, the average proportion of the weight 

 of the ovaries to that of the body is greater for every succeeding period 

 of ten days than for that of the preceding ten days. These averages show 

 that from the first ten days of January, when the average weight of the 

 ovaries of the clean salmon was only 0*35 per cent, of the weight of 

 the body, to the first ten days of November, when the average weight 

 of the ovary was 20 per cent, that of the body, the weight gradually in- 

 creases. The increase up to the 10th of May is almost imperceptible, 

 from that date onwards to the end of July it proceeds at a somewhat 

 quicker rate, throughout August rapidly, and from the beginning of 

 September very rapidly. To assist an estimate to be formed of the 

 difference in the degree of development of the genitalia of fish caught in 

 Holland to those of fish caught near Basle, Dr Hoek gives a diagram 

 showing, by means of two curves, the proportion of the weight of the 

 genitalia to the weight of the fish, one in regard to fish caught in 

 Holland, the other in regard to fish caught near Basle. He points out 

 that up to the beginning of June these curves run at an almost equal 

 distance from one another, only that the ovaries of fish caught near Basle 

 are about 0*5 per cent, further advanced than those of fish which have 

 only just left the sea. After the beginning of June both begin to show 

 somewhat greater energy in the growth of their sexual organs. These organs, 

 however, develop more rapidly in salmon of the upper Rhine. From 

 the beginning of August the sexual organs of the latter approach develop- 

 ment about twenty days in advance of those taken in Holland. By the 

 beginning of October, however, the condition of both fish is the same. 

 The ovaries of the fish taken in the upper Rhine reached about one- 

 fifth of their ripe weight during the first ten days of August, those of 

 the lower Rhine being about twenty days later. This would appear to 

 be an important stage in their development, as Professor Meischer 

 Ruesch states that he found, according to numerous investigations, that 

 the intestinal fat had at this time entirely disappeared, and that as the 



* Statistische und biologische Beitrage zur Kenntniss vou Leben des Rheinlachses 

 im Susswasser. Dr F. Meischer Ruesch, Prof. d. Physiol, in Basel. A contribution 

 to the literature of the Berlin Fisheries Exhibition of 1880. Publishers, Druck von 

 Metzger & Wittig, Leipsic. 



t Rapport over Statistische en biologische onderzoekingen ingesteld met behulp van 

 in Nederland gevaugen Zalmen. Dr P. P. O. Hoek, Wetenschappelijk Adviseur 

 in Visscherijzaken. 



