Lamprey To plane

Description

The lamprey to plane is characterized by a naked body anguilliforme covered with a smooth skin without scale secreting a strong quantity of mucus. It is of color blue-green, with the yellow sides and the white belly.

It measures in general from 12 to 20 cm for a weight of 2 with 5g. It is characterized by a mouth without jaw but equipped with a suction cup, and by the absence of even fins, in addition the caudal and dorsal fins are in contact. The respiratory openings, or spiracles, are always seven and to each one corresponds a pocket branchiale in the shape of bag. The lampreys absorb and reject water by the spiracles, at least at the adult stage, thanks to rapids contractions of the branchiaux bags. The absorption of water by the mouth is rare.

This species presents a sexual dimorphism, the male being smaller than the female in general.

The lamprey To plane is a ecotype with strictly river development of the River lamprey. (Their genetic codes are identical.)

Geographical distribution

Lampetra planeri, species very close to the fluviatile lamprey (Lampetra fluviatilis), has the same geographical distribution. Living only out of fresh water, it is present in the rivers and occasionally in the lakes at the North-West of Europe (Kelly and King, 2001). Its distribution extends from North and Eastern Europe to the Italian and Portuguese coasts.

Development and reproduction

A single reproduction

The reproduction is carried out in spring, mainly during May and April (P. Keith & Allardi, 2001), for a temperature ranging between 8 and 11°C. The period of abrasion is thus variable because of the temperature and can be spread out February at May. Sexual maturity is reached starting from a size of 9-15 cm.

The females build an oval nest of form, from 4 to 10 cm of depth according to the number of participants in his construction (Mug, 2000). To 30 individuals can reproduce on the same nest. The male is rolled up then around the female which is fixed on the bottom grace its suction cup. The fertilized eggs fall at the bottom from the nest where they are inserted in the sediments. Fruitfulness is rather high with 440.000 ovules/kg of live weight. After the reproduction the adults die, those reproduce only once during their life.

The larval phase

The lamprey To plane is characterized by a long larval phase, from 5 to 6 years. A few weeks after the reproduction, the larvae or ammocètes hatch, they do not measure whereas one centimetre and will hide in the sediments where they will develop. For this period, the larvae are very vulnerable. Indeed, much of young larvae are found in the stomachic contents of the trouts farios, a few weeks after the abrasion (Mug, 2000). On the contrary, mortality is relatively low during the remainder of the larval life (Hardisty, 1961).

Its mouth in the horseshoe shape being deprived of tooth, it traps its food present in the sediments or brought by the current, thanks to the mucus of its pharynx. The organic diatoms (blue algas) and refuses constitute the principal food of the larvae, but they can occasionally consume protozoa, nematodes or rotifères (Kelly and King 2001). The larva is completely blind for this period.

The metamorphosis

The passage of the larval stage to the adult (metamorphosis) generally lasts 3 to 10 months and takes place with the autumn (Hardisty & Potter 1971). Several morphological and physiological modifications are to be noted: - the genitals increase volume, - the digestive system is atrophied, preventing very taken food, - the dorsal fin develops and changes form, - the females acquire an anal fin, - the eyes become functional.

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