The zebrafish is an ideal vertebrate model for neurobehavioral studies with translational relevance to humans. Many aspects of sleep have been studied, but we still do not understand how and why sleep deprivation alters behavioral and physiological processes. A number of hypotheses suggest its role in memory consolidation. In this respect, the aim of this study was to analyze the effects of sleep deprivation on memory in zebrafish (Danio rerio), using an object discrimination paradigm. Four treatments were tested: control, partial sleep deprivation, total sleep deprivation by light pulses, and total sleep deprivation by extended light. The control group explored the new object more than the known object, indicating clear discrimination. The partially sleep-deprived group explored the new object more than the other object in the discrimination phase, suggesting a certain degree of discriminative performance. By contrast, both total sleep deprivation groups equally explored all objects, regardless of their novelty. It seems that only one night of sleep deprivation is enough to affect discriminative response in zebrafish, indicating its negative impact on cognitive processes. We suggest that this study could be a useful screening tool for cognitive dysfunction and a better understanding of the effect of sleep-wake cycles on cognition.

This study characterized a number of the behaviors of Farfantepenaeus subtilis in response to the offer of feed at different times during a 24 h cycle. Shrimp were observed under laboratory conditions during 12 h light-12 h dark cycles, before and immediately after feeding. The behaviors recorded were: burrowing, substrate exploration, vertical exploration, ingestion, swimming, inactivity, and crawling. The frequencies of all these behaviors increased in the presence of food, independent of time or light phase. The consumption of feed was more frequent in the morning. The results showed that the rhythm of activity is influenced by the light-dark cycle and the availability of food. The results are different from those reported for other shrimp species and indicate the potential value of understanding the behavioral details of each species for optimizing their management.

Emotional contagion has recently been described in fish but whether it is affected by familiarity is not known. We tested whether the sight of a distressed conspecific elicited fear in zebrafish, and whether this was modulated by familiarity. Groups of six zebrafish were housed together in the same tanks for 7 days to create familiar conditions. The behaviour of individual fish was then recorded in paired tanks within sight of either a familiar or an unfamiliar individual, before and after distilled water or an alarm substance was added to the demonstrator, but not to the observer. As expected, addition of distilled water did not elicit any behavioural change in either the demonstrator or the observer. However, addition of an alarm cue triggered anti-predatory behaviours in the demonstrator, which caused the expression of equivalent anti-predatory behaviours in the observer, suggesting the existence of fear contagion. Furthermore, the extent of fear contagion and behavioural matching was affected by familiarity, and observers matched the behaviour of the demonstrators more closely when they watched a distressed familiar neighbour than when they watched an unfamiliar fish. Our results have implications for fish welfare because they show that fish can become stressed by simply watching others become stressed. They also have implications for experimental design because fish housed in separate tanks cannot be assumed to be statistically independent if they can eavesdrop on their neighbours.

The zebrafish (Danio rerio) can be used in studies addressing the effects of drugs on learning, memory, and anxiety. In the present study, we investigated the effect of different alcohol treatments (chronic and acute) on the learning and anxiety response of zebrafish in an inhibitory avoidance paradigm. Zebrafish were initially exposed to different alcohol treatments and submitted to an inhibitory avoidance protocol, where an electroshock was applied to the fish as they swam from the white to the black side of a shuttle box tank (naturally preferred environment of zebrafish). Animals from the control and 0.5% acute alcohol groups exhibited high latency to enter the black side of the tank after the first exposure to electroshock, in addition to higher freezing and a shorter distance from the bottom of the tank, suggesting acute alcohol exposure did not affect aversive learning in zebrafish. However, chronic exposure and alcohol withdrawal impaired the fish's capacity to properly respond to the aversive stimulus. Overall, our results show the harmful effects of chronic alcohol exposure, both continued intake and its cessation, but avoidance behavior persisted and anxiety increased following acute alcohol exposure.