Fish living in the tidal fresh and brackish water reaches of the Zeeschelde Estuary were studied in samples collected from the cooling-water inlets of three power stations. Between July 1994 and June 1995, 42 different species were recorded including 26 marine migrants, 14 freshwater species and two diadromous species. Species number as well as fish abundance were correlated significantly with salinity and oxygen concentration. The community structure was analysed with a correlation biplot based on principal component analysis of the root-root transformed fish abundance. Four separated communities could be distinguished since the first principal component expressed a salinity and the second a temperature gradient. During summer and fall Pomatoschistus microps, P. minutus, P. lozanoi and Syngnathus rostellatus were most abundant in the brackish-water reach. At this time, freshwater species seemed to avoid the freshwater area. During winter, Sprattus sprattus, Clupea harengus and Dicentrarchus labrax were the dominant species of the brackish-water zone while the freshwater reaches were dominated by Gasterosteus aculeatus. Migrating fish such as Pleuronectes flesus, Lampetra fluviatilis, Anguilla anguilla and Osmerus eperlanus were restricted to the brackish environment. 1998 The Fisheries Society of the British Isles
By use of stow netting in the Zeeschelde Estuary, evidence is presented that the vertical distribution of fish changed at night. Demersal fish remained on the bottom during the day while at least a part of the populations present exploited surface water during the night. Pelagic fish maintained their position underneath the water surface throughout the day. 1999 The Fisheries Society of the British Isles ). While the ship was anchored, two nets on both sides were exposed to the tidal currents. The nets were 70 m in length with a stretched mesh size varying from 16 cm at the net mouth to 12 mm at the cod-end.During 2 weeks in November 1995, samples were taken between the water surface and 4 m, and between 4 m and the bottom ( 10 m), respectively. Samples taken between sunrise and sunset were categorized as day samples, other samples were night samples. In total, 20 samples were collected for this study (Table I). During the first week, high water was around midday and midnight; in the second week, high waters occurred at 0400 and 1600 hours. A description of the sampling area can be found in Maes et al. (1998).After each haul, fish were identified and counted. If necessary, sub-samples were taken by dividing the catch into equal parts. The water volume filtered by the net was calculated using the cross-sectional area of the net mouth, current velocity of the water and exact duration of each haul. Numbers of fish were transformed to numbers m 3 by dividing the total catch by the water volume sampled.One-way analysis of variance (ANOVA) was used to test the effect of depth, photoperiod and tidal stage on the root-root-transformed species abundance. Two-way ANOVA examined the interaction effects, depth photoperiod and depth tides. More than 7 10 5 individuals comprising 34 fish species were captured during the sampling period (Table II). Sprat Sprattus sprattus (L.) (67%) and herring Clupea harengus L. (29%) dominated the fish catches. Together with gobies Pomatoschistus spp.,
Oxytocin (OT) plays a pivotal role in a variety of complex social behaviors by modulating approach-avoidance motivational tendencies, but recently, its social specificity has been challenged. Here, a randomized, double-blind, placebo-controlled study was conducted with forty young adult men, investigating the effect of a single-dose of OT (24 IU) on behavioral and neural approach-avoidance. Frontal alpha asymmetry, indexing neurophysiological approach-avoidance, was obtained from electroencephalographic recordings while participants were presented with a series of pictures, individually rated in terms of personal relevance (i.e., high versus low positive/negative emotional evocativeness) and categorized as social or non-social. Additionally, participants could prolong (approach) or shorten (avoid) the viewing-time of each picture, providing a measure of behavioral approach-avoidance. Intranasal OT enhanced both behavioral and neural approach (increased viewing-time), particularly towards negatively valenced pictures of both social and non-social nature, thus challenging the notion that OT’s effects are specific to social stimuli. Neurally, OT specifically amplified approach-related motivational salience of stimuli that were self-rated to have high personal relevance, but irrespective of their social nature or rated affective valence (positive/negative). Together, these findings provide support to the General Approach-Avoidance Hypothesis of OT, suggesting a role of OT in amplifying the motivational salience of environmental stimuli with high (personal) relevance, but irrespective of their social/non-social nature.Clinical Trial Number: The study design was registered at ClinicalTrials.gov (NCT04443647; 23/06/2020; https://clinicaltrials.gov/ct2/show/NCT04443647).
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