Are lateralized and bold fish optimistic or pessimistic?

Abstract

Cognitive bias is defined as the influence of emotions on cognitive processes. The concept of the cognitive judgement bias has its origins in human psychology but has been applied to animals over the past 2 decades. In this study we were interested in determining if laterality and personality traits, which are known to influence learning style, might also be correlated with a cognitive bias in the three-spined sticklebacks (Gasterosteus aculeatus). We used the judgement bias test with the go/no-go procedure where fish were first trained to discriminate between a black and white card and, after reaching a minimum learning criterion, tested their response to an ambiguous card (grey). Optimistic subjects were expected to have a high expectation of reward associated with an ambiguous stimulus, whereas pessimistic subjects a high expectation of non-reward. We used an emergence and a mirror test to quantify boldness and laterality, respectively. We hypothesised that male, bolder and more strongly lateralized fish would be more optimistic than female, shy and less strongly lateralised fish. We found that males and more strongly lateralized fish were more optimistic than females and less strongly lateralized fish. In addition, bold males were more optimistic than shy males as we predicted, but females showed the opposite pattern. Finally, fish trained on the black colour card learned the training task faster than those trained on a white card. Our results indicate that both laterality and personality traits are linked to animals' internal states (pessimistic or optimistic outlooks) which likely has broad implications for understanding animal behaviour particularly in a welfare context.

Keywords: Boldness; Cognitive bias; Fish; Laterality; Learning; Optimism versus pessimism.

Fig. 1

Set up for the emergence test. Individuals had to emerge from the shelter (boldness) and then approach one of two mirrors on either side of the tank to score their laterality

Fig. 2

Training phase (a) with black or white cards placed on the left or right side of the testing arena. Probe test (b), time to approach the ambiguous stimulus, grey colour card placed in the centre of the tank. For a trial to commence, the subject had to be position in the centre of the far end of the arena. A food reward was delivered after the subject approached the correct card

Fig. 3

Mean time of three tests to approach the ambiguous stimuli during probe trials (MeanCT) as a function of the time to emerge from the shelter (Boldness) for females and males

Fig. 4

Strength of laterality with mean time to approach the ambiguous stimuli during probe trials (MeanCT). More strongly lateralised fish were faster to approach the ambiguous stimulus than less lateralised fish

Fig. 5

Mean and SE of the number of trials taken to reach the learning criterion during phase one (Attempts). Fish trained with a black card learned the task faster than those trained to approach the white card

Fig. 6

Comparison of the last five trials during the training phase with colours black or white and the probe test with the grey card