Rainbow trout discriminate 2-D photographs of conspecifics from distracting stimuli using an innovative operant conditioning device

Abstract

Cognitive abilities were studied in rainbow trout, the first continental fish production in Europe. Increasing public concern for the welfare of farmed-fish species highlighted the need for better knowledge of the cognitive status of fish. We trained and tested 15 rainbow trout with an operant conditioning device composed of self-feeders positioned in front of visual stimuli displayed on a screen. The device was coupled with a two-alternative forced-choice (2-AFC) paradigm to test whether rainbow trout can discriminate 2-D photographs of conspecifics (S+) from different visual stimuli (S-). The S-were applied in four stages, the last three stages representing increasing discrimination difficulty: (1) blue shapes; (2) black shape (star); (3) photograph of an object (among a pool of 60); (4) photograph of another fish species (among a pool of 60). Nine fish (out of 15) correctly managed to activate the conditioning device after 30-150 trials. The rainbow trout were able to discriminate images of conspecifics from an abstract shape (five individuals out of five) or objects (four out of five) but not from other fish species. Their ability to learn the category "fish shape" rather than distinguishing between conspecifics and heterospecifics is discussed. The successful visual discrimination task using this complex operant conditioning device is particularly remarkable and novel for this farmed-fish species, and could be exploited to develop cognitive enrichments in future farming systems. This device can also be added to the existing repertoire of testing devices suitable for investigating cognitive abilities in fish.

Environmental enrichment in fish aquaculture: A review of fundamental and practical aspects

“…274 In addition, several studies have demonstrated the ability of diverse farmed fish to recognise familiar conspecifics and consequent positive effects on social interactions. 29,146,275 Familiarity stabilises the hierarchical structure of a group, and governs behavioural modifications (e.g. agonistic behaviours) that promote feeding and growth, leading to higher fitness and survival.…”

“…cichlids), triggering aggressive responses with their mirror image in unresolved disputes, 143,144 which can lead to dysfunctional or even fearful states 145 . A recent study, using a complex operant conditioning device, demonstrated that rainbow trout are able to discriminate 2‐D photographs of conspecifics from different visual stimuli, suggesting the positive effects of developing visual‐based enrichments for fish cognition 146 . Therefore, there is ample scientific evidence that the use of visual stimuli as sensory enrichment can induce positive effects on fish welfare, despite the existence of important differences amongst light and colour sources, and species.…”

Does colour impact responses to images in geckos?

“…To understand if colour impacts the response to an object, especially biologically relevant versus novel, we selected two distinct objects: (1) an image of each gecko species and (2) an image of a car. A car was chosen as a random unfamiliar object as most likely geckos have never seen it before (for an example of the use of unfamiliar randomly selected objects see also Kleiber et al., 2021). For each object type (here called ‘image type’ Table 2), two different images of the same type (e.g., two individual geckos) were used to ensure that the responses obtained were not due to the specific image shown but rather the type of image itself (Fig.…”

“…To our knowledge, this is the only work that has investigated this issue and did so using only one species. The influence that colouration has on the response to objects when other confounding factors are removed remains unclear (see Kleiber et al., 2021 for a similar approach in fish). Here, we assess whether colour information changes the way geckos respond to different objects, and if the influence of colouration on the response depends on whether the object is familiar or novel.…”

Involvement of Taste Receptors in the Oro-Sensory Perception of Nutrients in Rainbow Trout (Oncorhynchus mykiss) Fed Diets with Different Fatty Acid Profiles

“…After the feeding period (9 : 00 -21 : 00 hours), RT could touch the trigger but no food reward would be provided. The conditionning period of RT to the self-feeder device was achieved in 10 days [41].To avoid oxidation of the diet and to stabilise the feed, pellets (stored in the dark and cool in an airtight bag) were regularly (every other day) added to the feeders.…”