This review presents a short survey of pertinent literature on rearing methods of pike-perch fry and fingerlings in ponds, net cages and tanks. The traditional pond culture results in variable numbers of fingerlings, which are sometimes small and are therefore of limited value for stocking. Fingerling production can be increased by manipulating the succession of zooplankton and by stocking adequate quantities of fry in the pond. Culture in illuminated net cages in lakes seems to be a possibility to produce advanced fry. The rearing of larvae in tanks following controlled propagation is initially based on feeding natural plankton. The artificial diet can only be used successfully several weeks later at fingerling size (4-5 cm). High mortality rates of fry and symptoms of food deficiency in liver cells indicate unsatisfactory quality of larval diets tested until now. Lack of an adequate artificial feed considerably hampers further development of intensive rearing of fry. Growth of fry and fingerlings is strongly temperature dependent. Growth is rather poor at 16-18°C and best between 26-30°C. Although there is a short stage of positive phototropism in fry, older pike-perch generally prefer dim light. There is no food uptake at high light intensity and mortalities will occur under such conditions. More research is needed on adequate diets which consider the ontogenetic development of the digestive organs of young fish. IntroductionThe number of fish species used in aquaculture is high (over 120 species worldwide) and is still increasing as the search for new species continues. Therefore, it is not surprising that pikeperch, although well-known to fish farmers, have recently attracted much attention.Schaperclaus (1961) indicated three major reasons for the cultivation of pike-perch as a secondary fish produced in common carp pond culture: a) to eliminate undesirable prey fish: b) to produce additional fish besides carp for the table and c) to produce pike-perch fingerlings for stocking. At least one of these reasons holds today, namely the production for restocking of natural waters, i.e., recreational fisheries.The rearing techniques available today differ for the various species currently being cultured. This depends not only on thc economic interest in a species, which may lead to considerable research efforts, but also on the existence of vulnerablc ontogenic development that sometimes reduce the possibilities of the controlled exploitation of a species.The pike-perch is not only an attractive game fish and presumably a key species in the biomanipulation of certain types

No abstract

Structural and functional relationships between oocytes and their envelopes were studied by means of electron microscopy in several teleost species after injection of live fish with horseradish peroxidase. The marker first appeared in the capillaries and the pericapillary spaces of the ovarian stroma. It then entered the collagen-filled spaces between the granulosa and theca cells; these spaces are in direct connection with the pericapillary spaces. The marker penetrated between the follicle cells and into the channels of the zona radiata surrounding the microvilli which traverse these channels. The marker was never found inside the microvilli or in the follicle cells; finally, it reached the surface of the oocytes and was internalized via micropinocytosis. Six stages in the course of folliculogenesis were observed, determined by (1) the formation of follicular and thecal cellular layers and a collagen-filled space between them, (2) the development of microvilli of oocytal and follicular origin, (3) the differentiation of the vitelline envelope and the pore channels, (4) pinocytotic activity of the oocytes, and (5) rapid growth of the oocyte and its envelopes during vitellogenesis.