Étude sur la répartition et le rôle piscicole de quelques Copépodes et Cladocères d'eau douce
Résumé
STUDY OF THE DISTRIBUTIONAND PISCICULTURAL ROLEOF CERTAIN FRESH-WATER COPEPODAAND CLADOCERA - I. — In the lakes of the Haute-Savoie and the Jura, as wellas in the ponds of the Bresse, the Côte-d'Or, and Lorraine, acertain number of species of Copepoda (excluding the group ofthe Harpacticoïda which has not been studied) and of Cladocerahave been discovered. In the lake of Montriond (Haute-Savoie) the quantitative variations, the temperature, and theoxygen have been susceptible of examination at the same timein the course of a year.II. — The discovery of the piscicultural function of thesespecies was then attempted by the examination of the stomachiccontents of 178 fish from the Lake of Geneva : bleak, roach,trout, char, powan, perch, and burbot. Sida crystallina (O. F.MÜLLER) plays an important part in the food of the perch, thechar, and the powan. Daphnia iongispina (O. F. MÜLLER),Bythotrephes iongimanus (F. LEYDIG), Leptodora Kindtii (F0CKE)are appreciated by the majority of the species. The bleakshows a predilection for Chydorus sphcericus (O. F. MÜLLER)and Acroperus harpce (BAIRD) (Chydoridae) while Simocephalusvetulus (O. F. MÜLLER) (Daphnida) a littoral species, has neverbeen found in this fish. The bleak has a special relish forMacrocyclops gigas (CLAUS), a deep-water species.In the stomach of a fish, a varied diet is not found but oftena single species represented by a large number of individuals.Must it be admitted that all these Entomostraca, certain ofwhich are however rare in the fisheries, live in compact swarms,or on the other hand that the fish chooses its food with extremecare ?1) VANDEL had noticed that with a normal net he did notcatch any Bythotrephes longimanus in Saint-Point lake (Jura),while with a net presenting a wide opening he had capturedas many as forty of them in vertical fishing.2) In a series of experiments some fry bred from a pelagicfish, the char, have been fed either with the lacustral animalculesof the Leman or with the animalcules of ponds : the fish havedisplayed indifference.The question of the choice of the species is therefore not yetsolved : it is not absolutely certain that the Entomostracadescribed as rare are so in fact, and a VANDEL remarks, thefood requirements of certain fish are still unknown.III. — In a systematic study of the function and the distributionof each of the species found, certain structural anomaliesof slight importance have been described (plate outside thetext). Cyclops strenuus (FISCHER) and Cyclops furcifer (CLAUS)recently separated are rather badly characterized. On theother hand Megacyclops gigas (CLAUS) and Megacyclops viridis(JURINE) recently distinguished by Roy (1932) are always welldefined.
Domaines
Sciences de l'environnement
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