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1. Various designs and techniques of closed system rearing of fish larvae are being developed using specific species chosen on the basis of their reproductive habits, ecological preference, and potential as environmental indicators. 2. The influence of the parameters of temperature, salinity, food, light, circulation, and the presence of autotropic organisms are tested using as criteria for the success of hatch and development. 3. To date, the results have produced several techniques which increase the percentage of success in raising fry and juvenile fishes.

Ultrastructural observations on spermiogenesis and spermatozoa of selected pyramidellid gastropods (species ofTurbonilla, Pyrgulina, Cingulina andHinemoa) are presented. During spermatid developement, the condensing nucleus becomes initially anterio-posteriorly compressed or sometimes cup-shaped. Concurrently, the acrosomal complex attaches to an electrondense layer at the presumptive anterior pole of the nucleus, while at the opposite (posterior) pole of the nucleus a shallow invagination is formed to accommodate the centriolar derivative. Midpiece formation begins soon after these events have taken place, and involves the following processes: (1) the wrapping of individual mitochondria around the axoneme/coarse fibre complex; (2) later internal metamorphosis resulting in replacement of cristae by paracrystalline layers which envelope the matrix material; and (3) formation of a glycogen-filled helix within the mitochondrial derivative (via a secondary wrapping of mitochondria). Advanced stages of nuclear condensation (elongation, transformation of fibres into lamellae, subsequent compaction) and midpiece formation proceed within a microtubular sheath (‘manchette’). Pyramidellid spermatozoa consist of an acrosomal complex (round to ovoid apical vesicle; column-shaped acrosomal pedestal), helically-keeled nucleus (short, 7–10 μm long, shallow basal invagination for axoneme/coarse fibre attachment), elongate helical midpiece (composed of axoneme, coarse fibres, paracrystalline and matrix materials, glycogen-filled helix), glycogen piece (length variable, preceeded by a dense ring structure at junction with midpiece). The features of developing and mature spermatozoa observed in the Pyramidellidae are as observed in opisthobranch and pulmonate gastropods indicating that the Pyramidelloidea should be placed within the Euthyneura/Heterobranchia, most appropriately as a member group of the Opisthobranchia.

A total of 262 specimens (0-, and 1-group) of Atlantic cod(Gadus morhua) representing 4 different yearclasses were caught in Trondheimsfjorden, Norway, during 1977–1984. They were genotyped by agar gel electrophoresis for the polymorphic haemoglobin locusHbI (Sick, 1961). The analyses revealed a highly significant (P=0.0003) heterogeneity ofHbI allele frequencies between yearclasses. The difference in the frequency of theHbI-1 allele between the first (1977) and the last (1983) yearclass amounted to 0.18 (±0.07). The results appear to support recent reports on considerable selection effects atHbI, and stress the unreliability of allele frequencies at this locus for use in studies of the genetic population structure of cod.

Die Entwicklung vonMonostroma grevillei zeichnet sich durch eine ungewöhnliche Variabilität aus (Schema Abb. 5). Der Lebenszyklus ist heteromorph mit einem einzelligen, kalkbohrenden Sporophyten (a). Parthenogenetische Gameten entwickeln sich zur Gestalt von Sporophyten; ihre Nachkommenschaft behält das Geschlecht der Ursprungspflanze bei (b). Ein kleiner Teil der zweigeißeligen Schwärmer kann unmittelbar wieder zu Gametophyten führen (c). Ganz ungewöhnlich ist die durch besondere Versuchsbedingungen bewirkte Entstehung beider Phänotypen sowie morphologischer Zwischenformen in der Nachkommenschaft eines einzelnen Sporophyten.

Many benthic species have been recorded to occur in the water column above the tidal flats in Königshafen. They were either passively suspended from the sediment or performed active migrations. Concerning both number of species and organisms, active migrations were more important. The causes for these migrations range from (1) individual escape from a sudden threat such as predator attack, over (2) group evasion of local subpopulations to avoid environmental deterioration, to (3) habitat changing of entire populations. The temporal scales involved range from seconds to seasons, and the spatial scales from cm to km. Such changes of distribution patterns have been demonstrated in juvenile molluscs and in meiofaunal copepods and plathelminths. Since migrations may interfere with many kinds of population studies in the field, new methods and concepts need to be developed to avoid and overcome pittalls. As a precaution, the migration potential of benthic species should be taken into account in any field study including population parameters.