In this study we investigate the social stimuli responsible for the increases in plasma hormones and in the availability of milt in male rainbow trout allowed to interact with sexually active females. Males were placed in five experimental groups receiving different levels of sensory contact with females: no sensory cues, chemical cues, chemical and visual cues, full sensory and behavioural interaction with a nesting ovulated female, full sensory and behavioural interaction with an inactive postspawning female. Plasma levels of 11-ketotestosterone, 17α,20β-dihydroxy-4-pregnen-3-one and gonadotrophin increased only in males allowed full sensory contact with nesting females. Levels of 11-ketotestosterone did not change in males receiving visual and chemical cues, and decreased in the three other groups of males. The amount of milt that could be stripped from males increased only in those males placed with active females. Spermatocrit did not differ among the groups.
Manipulation of the opportunity to spawn was used to investigate the relationship between endocrine events, egg viability and spawning behaviour in female rainbow trout. Females were prevented from spawning by isolating them from males and gravel for up to 21 days after ovulation. Blood samples were taken before pairing with a male, at the onset of nesting activity, and at the completion of spawning. Plasma hormone levels of gonadotropin (GtH) and 17a,20/7-dihydroxy-4-pregnen-3-one (17,2OP) were measured by specific radioimmunoassays. There were no qualitative or quantitative differences in the spawning behaviour of females paired on the day of ovulation or 7. 14, or 21 days after ovulation. There was a general decrease in the viability of eggs with increasing retention times. In females paired on the day of ovulation, or after 7 or 14 days, GtH levels increased with the onset of nesting behaviour and declined as fish reached the post-spawning condition. By day 2 I , GtH levels before pairing were significantly higher than prepairing levels in the other three treatment groups, and did not increase at the onset of nesting, or decrease in post-spawning fish. Plasma 17,20P remained high in pre-pairing and nesting samples of all four groups and declined to low levels in fish in post-spawning condition. In females paired on the day of ovulation there was a significant increase in 17,20P from the pre-pairing to the nesting stage. These results suggest that 17,20P plays a key role in the synchronization of behavioural and maturational events at the time of spawning.
RÉSUMÉLa réponse au stress induit par le transport a été étudiée chez des truites arc-en-ciel immatures d'un poids moyen de 200 g. D'une manière globale, les valeurs de l'hématocrite, de l'osmolarité du plasma sanguin, du Cortisol et de la testosterone sont significativement plus élevées chez les poissons transportés que chez les témoins non transportés, alors que les niveaux de gonadostimuline (GTH1 ) et d'hormone de croissance ne diffèrent pas suivant les lots. L'analyse du comportement en « open field » des individus de chaque lot montre que les poissons transportés s'immobilisent en moyenne après un temps significativement plus long que les témoins. L'étude des performances zootechniques de chaque lot pendant les deux mois suivant l'expérience indique que le lot transporté récupère rapidement.
The marine opisthobranch mollusc Aplysia punctata was cultured at the Laboratoire de Biologie Marine in Concarneau, France . A . punctata veligers settled and underwent metamorphosis on the alga Lomentaria articulata, but not on Ulva spp., Palmaria marina, Laminaria spp . and Fucus spp .
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