Insights from the judgment bias paradigm: Social group and tank size does not affect mental state in female guppies

Optimal holding conditions are key to animal welfare. How stressful husbandry is perceived by the animal can be determined via assessment of an animal's mental state - where it is positioned on the continuum between optimistic and pessimistic state - and can be measured using the judgment bias paradigm. In this test, individuals are trained to distinguish a rewarded from an unrewarded cue before being presented an ambiguous, intermediate cue. The response time to the ambiguous cue is then indicative of mental state. A shorter latency suggests a more positive (optimistic) mental state, a longer latency a more negative (pessimistic) mental state. Here, we used the judgment bias paradigm to assess the impact of standard laboratory housing conditions on the mental states of female guppies (Poecilia reticulata). As it is debated which holding conditions confer optimal welfare, we tested the impact of husbandry on mental state by keeping animals for three weeks in small or large social groups in either small or large tanks. We found that the different standard housing conditions we used did not lead to differences in mental state. As an unexpected side result, we found that female guppies seem lateral. Our findings of comparable mental state across housing conditions suggest that guppies either perceive the tested conditions as equally stressful or alternatively, that guppies are relatively resilient to the combination of group and tank sizes tested in this study. We conclude that the judgment bias paradigm can be a useful tool to assess fish welfare. This article is protected by copyright. All rights reserved.

Limitations of Spatial Judgment Bias Test Application in Horses (Equus ferus caballus)

Affective states are of increasing interest in the assessment of animal welfare. This research aimed to evaluate the possible limitations in the application of a spatial judgment bias test (JBT) in horses, considering the influence of stress level, personality traits, and the possible bias due to the test structure itself. The distinction between two positions, one rewarded (Positive) and the other not (Negative), was learned by 10 horses and 4 ponies,. Then, the latency to reach three unrewarded ambiguous positions (Near Positive, Middle, Near Negative) was measured. Furthermore, the validated Equine Behavior Assessment and Research Questionnaire (E-BARQ) was employed to assess personality traits. Fecal and hair cortisol levels were measured through radioimmunoassay (RIA), and the frequency of behavioral stress indicators was recorded. Results showed that horses that had the rewarded position (Positive) on the right approached Near Negative and Middle faster than those that had Positive on the left. Certain personality traits influenced the latency to reach Middle and Near Positive, but chronic stress did not seem to affect horses' judgment bias. This preliminary study highlighted several limitations in the employment of spatial JBT for the assessment of affective state in horses and that personality traits can partially influence the cognitive process. Further research is needed to refine the use of this test in horses, considering the peculiarities both of species and of individuals.