The Adhesive Organ of Larval Pike Esox Lucius L., (Pisces)

Abstract

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.

Temporal changes in vertical distribution, body orientation and mobility of pike (Esox luciusL.) free embryos: Individual observations under controlled conditions

“…vegetated river banks sloping down gradually). This behaviour is also interpreted as an adaptation to the static conditions of many spawning areas, allowing free early stages to avoid oxygen-depleted bottom waters (Kennedy, 1969;Machniak, 1975;Billard, 1996;Braum et al, 1996;Bry, 1996). However, it is striking to see that free embryos can be exposed to the environmental conditions of the sediment-water interface on two occasions: (1) up to several days during the resting phase, following a fall down to the bottom as an egg at spawning time or as a newly hatched; and (2) during the most extreme part of the break-off phase (c. one day around day 11).…”

“…Secretory granules are more numerous before hatching and it is believed that secretion after hatching is only a remaining activity of the gland cells: this would explain the fact that repeated adhesive behaviour induced by artificial disturbance leads to the prolonged loss of fastening ability (Braum et al, 1996).…”

“…Braum et al (1996) stated that "fastened free embryos remain inactive" and that "40 individuals observed over 10 minutes each remained motionless during 99% of the observation time". The present study clearly shows that displacements do occur, including during attachment behaviour.…”

“…During this phase, the young fish undergoes considerable anatomical and physiological transformations that result in the achievement of a mobile larva, capable of gill respiration and of capturing live prey (Balon, 1984). A number of authors have described pike post-hatching ontogeny as a sequence of events including the opening of mouth and anus, the transition from yolk sac epithelium respiration to gill respiration, the appearance of vibrating pectoral fins, the air filling of the swim bladder and the progressive shift from yolk sac nutrition to exogenous feeding (Dorier, 1938;Monten, 1948;Chimits, 1951;Tschörtner, 1956;Gihr, 1957;Shamardina, 1957;Braum, 1964;Girsa, 1969;Balvay, 1983;Raat, 1988;Braum et al, 1996). On the subject of spatial distribution, it has been unanimously noted that newly hatched pike typically move upward in the water column and attach themselves vertically to plant stems or leaves, or to decaying vegetation.…”

“…The adhesive cells or papillae are located on the front of the cephalic region and on both sides, slightly ahead of the eyes (Dorier, 1938;Monten, 1948;Tschörtner, 1956;Braum, 1964;Georges, 1964;Braum et al, 1996;Leslie and Gorrie, 1985;Cooper et al, 2008). Pike free embryos are reputed to be "inactive during the yolk-sac stage", until the transition from embryo to larva (Braum, 1978), and to spend a great part of yolk-sac stage "in a motionless position" (Raat, 1988;Braum et al, 1996). During the early post-hatching period, they were reported "to begin to swim only when the water is agitated" (Girsa, 1969).…”