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The effects of wall color stimuli on diving, and the effects of depth stimuli on scototaxis, were assessed in zebrafish. Three groups of fish were confined to a black, a white, or a transparent tank, and tested for depth preference. Two groups of fish were confined to a deep or a shallow tank, and tested for black-white preference. As predicted, fish preferred the deep half of a split-tank over the shallow half, and preferred the black half of a black/white tank over the white half. Results indicated that the tank wall color significantly affected depth preference, with the transparent tank producing the strongest depth preference and the black tank producing the weakest preference. Tank depth, however, did not significantly affect color preference. Additionally, wall color significantly affected shuttling and immobility, while depth significantly affected shuttling and thigmotaxis. These results are consistent with previous indications that the diving response and scototaxis may reflect dissociable mechanisms of behavior. We conclude that the two tests are complementary rather than interchangeable, and that further research on the motivational systems underlying behavior in each of the two tests is needed. [ABSTRACT FROM AUTHOR]

The open tank paradigm, also known as novel tank diving test, is a protocol used to evaluate the zebrafish behavior. Several characteristics have been described for this species, including scototaxis, which is the natural preference for dark environments in detriment of bright ones. However, there is no evidence regarding the influence of ''natural stimuli'' in zebrafish subjected to novelty-based paradigms. In this report, we evaluated the spatio-temporal exploratory activity of the short-fin zebrafish phenotype in the open tank after a short-period confinement into dark/bright environments. A total of 44 animals were individually confined during a 10-min single session into one of three environments: black-painted, white-painted, and transparent cylinders (dark, bright, and transparent groups). Fish were further subjected to the novel tank test and their exploratory profile was recorded during a 15-min trial. The results demonstrated that zebrafish increased their vertical exploratory activity during the first 6-min, where the bright group spent more time and travelled a higher distance in the top area. Interestingly, all behavioral parameters measured for the dark group were similar to the transparent one. These data were confirmed by automated analysis of track and occupancy plots and also demonstrated that zebrafish display a classical homebase formation in the bottom area of the tank. A detailed spatio-temporal study of zebrafish exploratory behavior and the construction of representative ethograms showed that the experimental groups presented significant differences in the first 3-min vs. last 3-min of test. Although the main factors involved in these behavioral responses still remain ambiguous and require further investigation, the current report describes an alternative methodological approach for assessing the zebrafish behavior after a forced exposure to different environments. Additionally, the analysis of ethologically-relevant patterns across time could be a potential phenotyping tool to evaluate the zebrafish exploratory profile in the open tank task. [ABSTRACT FROM AUTHOR]

Abstract: One of the most robust and readily measurable effects of moderate doses of ethanol on zebrafish behavior is locomotor hyperactivity. Two experiments were designed to examine the effects of repeated exposures to ethanol on ethanol-induced locomotor hyperactivity, and to determine whether these effects are context-dependent. Adult, wild-type zebrafish were given repeated exposure to ethanol in the presence of one contextual stimulus (A), while exposed to water in the presence of a second contextual stimulus (B). Exposure to ethanol consistently induced locomotor hyperactivity. After repeated exposures, animals tested with ethanol in the ethanol-paired context (A) showed sensitization of locomotor activity. When tested with ethanol in the unpaired context (B), however, sensitization was not observed. When tested in the absence of ethanol, there were no differences in responding to the paired and unpaired stimuli. This is the first demonstration of ethanol-induced locomotor sensitization in zebrafish. Moreover, this sensitization was context-specific, indicating that learning can modify drug-induced behaviors in zebrafish. [Copyright &y& Elsevier]

Animal behaviour is the interaction between environment and an individual organism, which also can be influenced by its neighbours. Variations in environmental conditions, as those caused by contaminants, may lead to neurochemical impairments altering the pattern of the behavioural repertoire of the species. Atrazine (ATZ) is an herbicide widely used in agriculture that is frequently detected in surface water, affecting non-target species. The zebrafish is a valuable model organism to assess behavioural and neurochemical effects of different contaminants since it presents a robust behavioural repertoire and also all major neurotransmitter systems described for mammalian species. The goal of this study was to evaluate the effects of subchronic ATZ exposure in defensive behaviours of zebrafish (shoaling, thigmotaxis, and depth preference) using the split depth tank. Furthermore, to investigate a putative role of cholinergic signalling on ATZ-mediated effects, we tested whether this herbicide alters acetylcholinesterase (AChE) activity in brain and muscle preparations. Fish were exposed to ATZ for 14 days and the following groups were tested: control (0.2% acetone) and ATZ (10 and 1000 μg/L). The behaviour of four animals in the same tank was recorded for 6 min and biological samples were prepared. Our results showed that 1000 μg/L ATZ significantly increased the inter-fish distance, as well as the nearest and farthest neighbour distances. This group also presented an increase in the shoal area with decreased social interaction. No significant differences were detected for the number of animals in the shallow area, latency to enter the shallow and time spent in shallow and deep areas of the apparatus, but the ATZ 1000 group spent significantly more time near the walls. Although ATZ did not affect muscular AChE, it significantly reduced AChE activity in brain. Exposure to 10 μg/L ATZ did not affect behaviour or AChE activity. These data suggest that ATZ impairs defensive behaviours of zebrafish, which could be related to its action on brain cholinergic neurotransmission. Moreover, the use of the split depth tank could be an alternative strategy to assess group behaviour and depth preference after exposure to chemical compounds. [ABSTRACT FROM AUTHOR]

Highlights: [•] Short-term hypoxia produced four distinct behavioral stages in adult zebrafish. [•] Brain damage and behavioral impairments were observed in zebrafish after hypoxia. [•] Effects induced by hypoxia were reversed after recovery under normoxic conditions. [•] Behavioral impairments recovered more quickly than brain damage following a return to normoxic conditions. [Copyright &y& Elsevier]