Impairments in spatial learning by telencephalic lesions in Japanese eels (Anguilla japonica)

Analysis of visual discrimination in Japanese eel (Anguilla japonica)

Japanese eels were trained to discriminate between a checkerboard panel and a plain gray panel in a circular pool with three pipes. One of the pipes was open, whereas the others were closed. The correct choice of discriminative stimulus was reinforced by entering the pipe. When the panels were displayed vertically (on the wall), the eels successfully learned discrimination, but they were unable to acquire the task when the panels were presented horizontally (on the floor). Enucleation of the retina impaired discrimination, whereas ablation of the olfactory plates did not. In the second experiment, the eels underwent three tests after discriminative training with vertical stimuli displayed. When plain black or white panels were presented instead of a checkerboard panel, the eels could not discriminate. Thus, the discriminative stimulus must have both black and white components. The eels exhibited a generalization gradient along the fines of the checkerboard. Finally, the pallium was damaged by coagulation, and the eels did not maintain the discrimination after the lesions. The behavioral deficits were classified into successful relearning and no relearning. Damage to the dorso-lateral (DL) or dorso-central (DC) pallium was associated with severe impairment (no relearning), although it was not possible to isolate the particular brain area or combination of brain areas which was required. The DL damage probably causes memory deficits, but the deficits caused by the DC damage might be motor or motivational deficits.

Finding navigation cues near fishways

Many fish species depend on migration for various parts of their life cycle. Well-known examples include diadromous fish such as salmon and eels that need both fresh water and salt water to complete their life cycle. Migration also occurs within species that depend only on fresh water. In recent decades, anthropogenic pressures on freshwater systems have increased greatly, and have resulted, among other effects, in drastic habitat fragmentation. Fishways have been developed to mitigate the resulting habitat fragmentation, but these are not always effective. To improve fishway efficiency, the variety of navigation cues used by fish must be better understood: fish use a multitude of sensory inputs ranging from flow variables to olfactory cues. The reaction of a fish is highly dependent on the intensity of the cue, the fish species involved, and individual traits. Recently developed monitoring technologies allow us to gain insights into different combinations of environmental and physiological conditions. By combining fish behavioural models with environmental models, interactions among these components can be investigated. Several methods can be used to analyse fish migration, with state-space models, hidden Markov models, and individual-based models potentially being the most relevant since they can use individual data and can tie them to explicit spatial locations within the considered system. The aim of this review is to analyse the navigational cues used by fish and the models that can be applied to gather knowledge on these processes. Such knowledge could greatly improve the design and operation of fishways for a wider range of fish species and conditions.

Alarm cues and alarmed conspecifics: neural activity during social learning from different cues in Trinidadian guppies

Learning to respond appropriately to novel dangers is often essential to survival and success, but carries risks. Learning about novel threats from others (social learning) can reduce these risks. Many species, including the Trinidadian guppy (Poecilia reticulata), respond defensively to both conspecific chemical alarm cues and conspecific anti-predator behaviours, and in other fish such social information can lead to a learned aversion to novel threats. However, relatively little is known about the neural substrates underlying social learning and the degree to which different forms of learning share similar neural mechanisms. Here, we explored the neural substrates mediating social learning of novel threats from two different conspecific cues (i.e. social cue-based threat learning). We first demonstrated that guppies rapidly learn about threats paired with either alarm cues or with conspecific threat responses (demonstration). Then, focusing on acquisition rather than recall, we discovered that phospho-S6 expression, a marker of neural activity, was elevated in guppies during learning from alarm cues in the putative homologue of the mammalian lateral septum and the preoptic area. Surprisingly, these changes in neural activity were not observed in fish learning from conspecific demonstration. Together, these results implicate forebrain areas in social learning about threat but raise the possibility that circuits contribute to such learning in a stimulus-specific manner.