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Notes: The changes during the life cycle in the relative length of certain parts of the alimentary tract, buccal-pharyngeal cavity, oesophagus-stomach, intestine, rectum—are investigated in the five North Sea flatfish species, viz. turbot, brill, plaice, dab, sole. According to the average ratio between the length of the alimentary tract and the food preference three main groups are distinguished.

Notes: Abstract. The Atlantic salmon, Salmo salar L., was once of major importance to the fishing industry along the River Rhine. This paper discusses the Dutch and German salmon catches over the years 1863–1950. Even up to the end of the last century, it was not uncommon for Dutch and German fishermen to land 100000 salmon a year. However, factors such as the increased use of locks and weirs along the Rhine, coupled with growth in pollution, soon led to a rapid decline in numbers. By 1933, the salmon fishing industry in the Netherlands had virtually ceased to exist. Analysis of the available catch statistics suggests that the decline in the salmon population could have started before official records began.Although the degree of scatter in the data and uncertainties in the assumptions preclude the possibility of drawing firm conclusions about the survival rate of salmon, these figures illustrate how difficult it will be to maintain a stable population in the Rhine. Moreover, a number of changes have taken place since the heyday of salmon in western Europe, which could compound the problem. Of particular importance in the context of the Rhine are:〈list xml:id="l1" style="custom"〉1 the closure of two of the major migration routes to the sea (Haringvliet and Zuiderzee);2 morphological changes in the river;3 chemical and thermal pollution;4 the loss of accessible spawning and nursery areas of the required quality;5 the disappearance of salmon from other rivers that flow into the North Sea such as the Rivers Elbe, Weser and Ems. If salmon were only reintroduced into the Rhine, a certain proportion would probably stray and infiltrate these other rivers.The fact that the impact of these changes is difficult to quantify increases the uncertainty associated with maintaining a stable stock of salmon in the Rhine.

Notes: The rapid increase of the mining for marine gravels in the North Sea offers a serious threat to the marine environment and especially for the herring populations of the southern North Sea and Channel. The paper reviews the literature dealing with the herring and its spawning ground, behaviour, abiological characteristics—type of substrate, depth, salinity, temperature and current velocity. A hypothesis is made that sound may play an important role in guiding the herring to its spawning site.

Notes: Turbot (11–70 cm long) and brill (21–70 cm long) were collected in the summer of 1968 north of the Brown Bank, Texel Hole and were infected by Bothriocephalus scorpii. Infections occurred even in the first year of life of the fish. In turbot, with increasing length, the average weight of tapeworm rose from 0–6 to 14-9 g/flsh. Brill were less commonly infected and then only slightly. The intermediate host of the tapeworm seems to be Gobius species, upon which juvenile turbot and brill prey most.

Notes: The ambivalent behaviour of the Greenland halibut with respect to its swimming position is discussed. The conclusion is that, when swimming close to the bottom, it swims the way all flatfishes do, viz. horizontally; when it swims freely, however, it adopts a vertical position.

Notes: Although coregonids (Coregonus albula, C. lavaretus) were abundant in Dutch waters for centuries, data on catch are available beginning only in 1910. The highest recorded catch was 14.6 tons in 1915; however, in 1918, commercial fishery came to an end. Extensive restocking attempts between 1907–1938 failed. At present, a few specimens are still caught each year from releases and restocking programmes in the Federal Republic of Germany. Migratory (anadromous) smelt (Osmerus eperlanus) was once an important fish in the Zuiderzee and Rhine-Scheldt estuary, but with completion of an enclosure dam in 1932, the Zuiderzee fishery came to an end. Smelt fishery in the lower reaches of the Rhine ended in 1966 when the “Delta-works” were completed in Holland's Diep and Haringvliet.〈section xml:id="abs1-2"〉〈title type="main"〉RésuméDéclin de la pêche de corégonides et d'éerlan migrateur dans le Bas-Rhin, Pays-BasBien que les coregonides (Coregonus albula, C. lavaretus) étaient nombreux dans les eaux du Pays-Bas pendant des siècles, les données sur la pêhe ne commençent qu‘ en 1910. La prise la plus grande enregistrée étair de 14.6 tonnes en 1915. En 1918, la pêche commerciale arrivait sà son terme. Des efforts intenses de repeuplement entre 1907 et 1938 ne réussissaient pas. Aujourd'hui, quelques exemplaires sont encore pris chaue année provenant de libérations et de programmes de repeuplement de la République Fédérale d'Allemagne. L’éperlan migrateur (anadrome, Osmerus eperlanus) était un poissons important dans le Zuidersee et dans l'estuaire du Rhin-Scheldt. En 1932, avec la fermeture de la digue de rotection de la Zuidersee, la pêhe dans la Zuidersee était terminée. En 1966, la peêche d‘éperlanf dans la région basse du Rhin sà pris terme quand les “Delta-Works”étaient completés dans l'Hollands Diep et I'Haringvliet.〈section xml:id="abs1-3"〉〈title type="main"〉ZusammenfassungRückgang der Fánge von Coregoniden und wandernden Stinten im niederländischen UnterrheinObwohl Coregoniden (Coregonus albula, C. lavaretus) über Jahrhunderte in holländischen Gewässern sehr zahlreich waren, wurden Fangdaten erst seit etwa 1910 ermittelt. Die höchste Fangmenge wurde mit 14,6 to im Jahre 1915 erzielt. Um 1918 kam bereits die kommerzielle Fischerei zum Erliegen. Umfangreiche Besatzmßnahmen zwischen 1907 und 1938 schlugen fehl. Gegenwärtig werden noch immer jedes Jahr wenige Exemplare gefangen, die von Besatzmßnahmen in der Bundesrepublik stammen. Die Wanderform des Stints (Osmerus eperlanus) war einst ein wichtiger Fisch in der Zuiderzee und im Rhein-Schelde-Aestuar, jedoch brach die Fischerei nach dem Bau des Abschlußdeiches im Jahre 1932 zusammen. Die Stindischerei kam im unteren Rheingebiet im Jahre 1966 zum Erliegen, nachdem die Bauten des “Delta-Werks” im Holland's Diep und dem Haringvliet abgeschlossen waren.