Eels' individual migratory behavior stems from a complex syndrome involving cognition, behavior, physiology, and life history.

Variability within species is key for adaptability and biological evolution. To understand individualities in the context of animal movement, we focused on one of the most remarkable migrations-the journey of the endangered European eel from their birthplace in the Sargasso Sea to freshwater environments. Laboratory observations unveiled a continuum of diverse phenotypes of migrating eels: Some displayed a heightened tendency to swim against a constant water flow, while others a greater propensity to climb obstacles.

Exploring the Importance of Environmental Complexity for Newly Hatched Zebrafish.

The effects of an early impoverished social or physical environment on vertebrate neural development and cognition has been known for decades. While existing studies have focused on the long-term effects, measuring adult cognitive phenotypes, studies on the effects of environmental complexity on the early stages of development are lacking. Zebrafish () hatchlings are assumed to have minimal interaction with their environment and are routinely reared in small, bare containers.

Shortest path choice in zebrafish (Danio rerio).

Many animals regularly move between different locations within their home range. During these journeys, individuals are expected to use the shortest path, because this strategy minimizes energy expenditure and reduces exposure to adverse conditions, such as predation. The ability to find the shortest distance route has been demonstrated in ants, migrating birds and a few mammals.

Interspecific differences in developmental mode determine early cognitive abilities in teleost fish.

Most studies on developmental variation in cognition have suggested that individuals are born with reduced or absent cognitive abilities, and thereafter, cognitive performance increases with age during early development. However, these studies have been mainly performed in altricial species, such as humans, in which offspring are extremely immature at birth. In this work, we tested the hypothesis that species with other developmental modes might show different patterns of cognitive development.

Extra food provisioning does not affect behavioral lateralization in nestling lesser kestrels.

Costs and benefits of brain lateralization may depend on environmental conditions. Growing evidence indicates that the development of brain functional asymmetries is adaptively shaped by the environmental conditions experienced during early life. Food availability early in life could act as a proxy of the environmental conditions encountered during adulthood, but its potential modulatory effect on lateralization has received little attention.

Quantity discrimination in newly hatched zebrafish suggests hardwired numerical abilities.

An intriguing hypothesis to explain the ubiquity of numerical abilities is that all vertebrates are born with hardwired neuronal networks for processing numbers. To date, only studies on human foetuses have clearly supported this hypothesis. Zebrafish hatch 48-72 h after fertilisation with an embryonic nervous system, providing a unique opportunity for investigating this hypothesis.

Learning and visual discrimination in newly hatched zebrafish.

With the exception of humans, early cognitive development has been thoroughly investigated only in precocial species, well developed at birth and with a broad behavioral and cognitive repertoire. We investigated another highly altricial species, the zebrafish, , whose embryonic development is very rapid (< 72 h). The hatchlings' nervous system is poorly developed, and their cognitive capacities are largely unknown.

Environmental enrichment decreases anxiety-like behavior in zebrafish larvae.

The development of anxiety disorders is often linked to individuals' negative experience. In many animals, development of anxiety-like behavior is modeled by manipulating individuals' exposure to environmental enrichment. We investigated whether environmental enrichment during early ontogenesis affects anxiety-like behavior in larval zebrafish.

Guppies () are deceived by visual illusions during obstacle negotiation.

Animals travelling in their natural environment repeatedly encounter obstacles that they can either detour or go through. Gap negotiation requires an accurate estimation of the opening's size to avoid getting stuck or being injured. Research on visual illusions has revealed that in some circumstances, transformation rules used to generate a three-dimensional representation from bidimensional retinal images fail, leading to systematic errors in perception.

Zebrafish excel in number discrimination under an operant conditioning paradigm.

Numerical discrimination is widespread in vertebrates, but this capacity varies enormously between the different species examined. The guppy (Poecilia reticulata), the only teleost examined following procedures that allow a comparison with the other vertebrates, outperforms amphibians, reptiles and many warm-blooded vertebrates, but it is unclear whether this is a feature shared with the other teleosts or represents a peculiarity of this species. We trained zebrafish (Danio rerio) to discriminate between numbers differing by one unit, varying task difficulty from 2 versus 3 to 5 versus 6 items.

Stimulus characteristics, learning bias and visual discrimination in zebrafish (Danio rerio).

Zebrafish is an emerging model in the study of brain function; however, knowledge about its behaviour and cognition is incomplete. Previous studies suggest this species has limited ability in visual learning tasks compared to other teleosts. In this study, we systematically examined zebrafish's ability to learn to discriminate colour, shape, size, and orientation of figures using an appetitive conditioning paradigm.

Automated Operant Conditioning Devices for Fish. Do They Work?

The growing use of teleosts in comparative cognition and in neurobiological research has prompted many researchers to develop automated conditioning devices for fish. These techniques can make research less expensive and fully comparable with research on warm-blooded species, in which automated devices have been used for more than a century. Tested with a recently developed automated device, guppies () easily performed 80 reinforced trials per session, exceeding 80% accuracy in color or shape discrimination tasks after only 3-4 training session, though they exhibit unexpectedly poor performance in numerical discrimination tasks.

Continuous versus discrete quantity discrimination in dune snail (Mollusca: Gastropoda) seeking thermal refuges.

The ability of invertebrates to discriminate quantities is poorly studied, and it is unknown whether other phyla possess the same richness and sophistication of quantification mechanisms observed in vertebrates. The dune snail, Theba pisana, occupies a harsh habitat characterised by sparse vegetation and diurnal soil temperatures well above the thermal tolerance of this species. To survive, a snail must locate and climb one of the rare tall herbs each dawn and spend the daytime hours in an elevated refuge position.

Poor numerical performance of guppies tested in a Skinner box.

We tested the hypothesis that part of the gap in numerical competence between fish and warm-blooded vertebrates might be related to the more efficient procedures (e.g. automated conditioning chambers) used to investigate the former and could be filled by adopting an adapted version of the Skinner box in fish.

Susceptibility to Size Visual Illusions in a Non-Primate Mammal ().

The perception of different size illusions is believed to be determined by size-scaling mechanisms that lead individuals to extrapolate inappropriate 3D information from 2D stimuli. The Muller-Lyer illusion represents one of the most investigated size illusions. Studies on non-human primates showed a human-like perception of this illusory pattern.

The devil is in the detail: Zebrafish learn to discriminate visual stimuli only if salient.

Due to their unique characteristics, the zebrafish plays a key role in the comprehension of neurobiology of cognition and its pathologies, such as neurodegenerative diseases. More and more molecular tools for this aim are being developed, but our knowledge about the cognitive abilities of zebrafish remains extremely scarce compared to other teleost fish. We aimed to investigate the complex cognitive abilities of zebrafish using a tracking-based automated conditioning chamber that allowed precise experimental control, avoided potential cueing provided by the observer (Clever Hans phenomenon), and was shown to considerably improve learning in other teleosts.

Vegetation cover induces developmental plasticity of lateralization in tadpoles.

Lateralization of cognitive functions influences a large number of fitness-related behaviors and shows, in most species, substantial variation in strength and direction. Laboratory works and field data have suggested that this variation is often due to adaptive phenotypic plasticity. Strong lateralization should be favored in some ecological conditions, for example, under high risk of predation.

Male and female guppies differ in problem-solving abilities.

In a number of species, males and females have different ecological roles and therefore might be required to solve different problems. Studies on humans have suggested that the 2 sexes often show different efficiencies in problem-solving tasks; similarly, evidence of sex differences has been found in 2 other mammalian species. Here, we assessed whether a teleost fish species, the guppy, , displays sex differences in the ability to solve problems.

Measuring recognition memory in zebrafish larvae: issues and limitations.

Recognition memory is the capacity to recognize previously encountered objects, events or places. This ability is crucial for many fitness-related activities, and it appears very early in the development of several species. In the laboratory, recognition memory is most often investigated using the novel object recognition test (NORt), which exploits the tendency of most vertebrates to explore novel objects over familiar ones.

The ontogeny of continuous quantity discrimination in zebrafish larvae (Danio rerio).

Several studies have investigated the ontogeny of the capacity to discriminate between discrete numerical information in human and non-human animals. Contrarily, less attention has been devoted to the development of the capacity to discriminate continuous quantities. Recently, we set up a fast procedure for screening continuous quantity abilities in adult individuals of an animal model in neurodevelopmental research, the zebrafish.

Guppies show sex and individual differences in the ability to inhibit behaviour.

In humans, individual and sex differences have been long reported for several cognitive tasks and are at least in part due to variability in the function that inhibits behaviour (i.e. inhibitory control).

Size discrimination in adult zebrafish (Danio rerio): Normative data and individual variation.

In humans, aging and neurodegenerative diseases have been found to be associated with impairment in both mathematical abilities and estimation of continuous quantities such as size, weight or distance. Zebrafish (Danio rerio) is rapidly becoming a model for human aging and brain disorders but we currently lack any instrument for rapid assessment of quantity estimation abilities in this species. Here we developed a simple method based on spontaneous preference of zebrafish for using the larger available hole to pass an obstacle.

Alarm cue-mediated response and learning in zebrafish larvae.

We investigated the behavioural and learning response of zebrafish larvae to chemicals released by injured conspecifics (the alarm cue). Many aquatic vertebrates and invertebrates exhibit an innate antipredator response to alarm cues because in nature, they reliably indicate the presence of predators. Likewise, when an individual simultaneously perceives a novel odour and alarm cue, it learns to recognise the novel odour as a predator odour.

Honeybees use absolute rather than relative numerosity in number discrimination.

Various vertebrate species use relative numerosity judgements in comparative assessments of quantities for which they use larger/smaller relationships rather than absolute number. The numerical ability of honeybees shares basic properties with that of vertebrates but their use of absolute or relative numerosity has not been explored. We trained free-flying bees to choose variable images containing three dots; one group ('larger') was trained to discriminate 3 from 2, while another group ('smaller') was trained to discriminate 3 from 4.

Factors affecting the measure of inhibitory control in a fish (Poecilia reticulata).

Inhibitory control allows an individual to block automatic responses as well as to control behaviour and attention. There is growing evidence that many species possess this ability, although the difference in performance among species is great. Inhibitory control has been frequently measured using the detour task: a desired reward is placed behind a transparent barrier, and the animal has to inhibit the tendency to directly move toward the goal, instead making a detour around the barrier.