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Newly hatched pike laryae swim by lateral movements of the trunk. The swimming path is directed upwards. They do not avoid obstacles but interrupt any movements immediately when colliding a substrate. Paired cement glands in rostro-nasal position excrete an elastic connection between larva and the touched substrate. Larvae spend yolk sac stage in a motionless position.The glands were studied by scanning electron microscope, by lightmicroscope and transmission electron microscope. The organs consist of two rostro-lateral areas which have a striking sculptured surface.The glandular cells are of the high prismatic type with basic nuclei and granulae in the apical parts. The granulae are already reduced in size and number after hatching against the prehatching stage. This indicates an early secretory activity before an attachement occured.There are grounds to consider mainly two ecological aspects in favour of pike larvae attached to substrates. One is the distance from the bottom water layers which are often characterized by oxygen deficiency and low water currents. Because pike larvae develop their gills later the gas exchange occurs with the body surface. Favourable water circulation normally exists in some distance from sediment and improves the respiration.The second aspect is governed by immobility and pigmentation which camoullage larvae against predators.

Naturally spawned egg strands of perch, PercaJluviatilis L. were sampled from exposed fir trees submerged in Lake Plufisee, Holstein, Northern Germany from April to May 1989. These were incubated in sifu and in the laboratory to estimate the viability, development and abnormalities of the embryos. From the in siru incubated eggs 91.6% embryos were viable, the nonviable portion comprising 1.1 % unfertilized eggs, 5.1 % dead and 2.2 % with abnormalities. As compared to the eggs incubated in the laboratory with 84.1 % viable embryos, the nonviable portion consisting 1.1 % unfertilized eggs, 11.3 % dead and 3.5 % with abnormalities. Incubation rate of P. fluviatilis embryos both in situ and laboratory, ranged from 200-210 ATUs (10 "C in situ and 8 O C in the laboratory) with incubation period of 20-27 days from fertilization to 50 % hatching.