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image of Crustaceana

The influence of rearing conditions on cyst production and hatching in the fairy shrimp Chirocephalus ruffoi was evaluated by rearing freshly hatched nauplii under two different conditions: in indoor culture at constant temperature and photoperiod, and in outdoor culture under naturally fluctuating temperature and varying photoperiod. Comparison of the quantitative reproductive characteristics of all the females tested revealed significant differences between the two groups, as to frequency of deposition (P < 0:01), clutch size (P < 0:001), and life span (P < 0:01). After dehydration, the cysts produced under natural culture conditions hatched, whereas those produced under constantly controlled conditions did not. The latter required a thermal shock for hatching as a further stimulus. The hatching pattern was more or less similar in the two cyst samples (first nauplii after 4 days of incubation, peak within 3 days), and the percentage of nauplii hatched did not significantly differ (P > 0:05). Submitting undehydrated, freshly laid cysts to three different subsequent stimuli (dilution, thermal shock, dehydration) gave very different results depending on the conditions under which cysts were produced. Whereas hatching was minimal for those laid under outdoor fluctuating conditions (2%), cysts produced at constant conditions showed a much higher hatching percentage (46.7%). Furthermore, in the latter, both quiescent and diapausing "eggs" were observed within the same clutch, though in different proportions. Irrespective of the culturing conditions, the phenomenon of hatching was characterized by a very erratic pattern. An extremely high variation was observed within the clutches of a single female, as well as among different females. Such a variation was independent of female age, clutch order, and clutch size.

L'influence des conditions d'elevage sur la production des oeufs de resistance et l'eclosion chez l'anostrace Chirocephalus ruffoi a ete evaluee en elevant des nauplii fraochement eclos sous deux conditions differentes: un elevage au laboratoire a temperature et photoperiode constantes et un elevage a l'exterieur a temperature et photoperiode variant naturellement. La comparaison des caracteristiques quantitatives de la reproduction de toutes les femelles testees revelent des differences significatives entre les deux groupes comme la frequence de ponte (P < 0;01), la taille de la ponte (P < 0;001) et la duree de vie (P < 0;01). Apres deshydratation, les oeufs de resistance produits en conditions naturelles ont eclos mais non ceux produits en conditions constantes controlees. Ces derniers ont necessite d'un choc thermique comme stimulus pour eclore. Le modele d'eclosion etait plus ou moins similaire dans les deux echantillons d'oeufs (premier nauplius apres 4 jours d'incubation, pic en 3 jours), et le pourcentage de nauplii eclos n'etait pas significativement different (P > 0,05). En soumettant des oeufs fraochement pondus, non d eshydrates a trois stimuli differents (dilution, choc thermique, deshydratation), des resultats tres differents ont ete obtenus suivant les conditions de production des oeufs de resistance. Tandis que l'eclosion etait minimale chez ceux pondus en conditions exterieures fluctuantes (2%), ceux produits en conditions constantes ont montre un pourcentage d'eclosion beaucoup plus eleve (46,7%). De plus, dans ce dernier cas, des oeufs immediats aussi bien que des oeufs de resistance ont ete observes dans une meme ponte, bien qu'en proportions differentes. Independamment des conditions d'elevage, le phenomene d'eclosion etait caracterise par un modele tres irregulier. Une variation extremement elevee a ete observee dans les pontes d'une meme femelle, et egalement entre differentes femelles. Une telle variation etait independante de l'age de la femelle, du rang de la ponte et de sa taille.


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