2.1. Original Conceptualizations of Positive Animal Welfare

Fraser and Duncan [ 7 ] were among the first welfare researchers to propose incorporating measures of positive affect into welfare assessment. They reasoned that if animals experience negative affective states (pain, hunger/thirst, fear, exhaustion, etc.), evolutionary theory suggests they should experience positive affective states as well. According to Fraser and Duncan [ 7 ], motivational affective states (MASs) evolved as separate processes to solve two different types of motivational problems; survival situations (what the animal needs) and opportunity situations (what the animal wants/likes). In both scenarios, the animal’s affective state and resulting behavioral responses usually result in an evolutionarily advantageous outcome where the net outcome of the action on the animal’s fitness is positive. Affective states are triggered by internal or external stimuli and subsequently motivate certain types of behavioral responses which can be positive (pleasure, joy, excitement, fulfillment, etc.) or negative (pain, hunger/thirst, fear, exhaustion, etc.). From an evolutionary standpoint, it is therefore in the animal’s best interest to avoid prolonged negative affective states and promote positive states in order to optimize fitness.

Fraser and Duncan [ 7 ] suggested that analyzing behavior using their conceptual framework of positive and negative affect is necessary in order to generate a comprehensive assessment of an animal’s welfare. Historically, welfare research has largely focused on mitigating prolonged need situations, i.e., those in which the animal is required to perform an action necessary to cope with threats to their survival and the resulting negative affective states, such as fleeing from a predator or searching for water during a drought. While providing relief from need situations will have a net beneficial effect on poor animal welfare, the most this approach can accomplish is to raise the welfare status from poor to neutral. While prolonged need situations are detrimental to animal welfare, their absence does not indicate positive affect. Fraser and Duncan [ 7 ] argued that providing animals with situations to promote positive affective states such as pleasure and joy are necessary to improve welfare past the neutral point. This work provided the imperative to incorporate positive welfare markers and use a combination of behavioral analysis and life history knowledge to predict when an aspect of animal management is likely to cause a positive reaction.

While the evolutionary theory and behavioral observations discussed by Fraser and Duncan [ 7 ] strongly suggested that positive emotions are not exclusive to humans, there was still little practical information regarding ways to promote positive affect in animals. Yeates and Main [ 15 ] were among the first ethologists to compile and publish a comprehensive review of positive welfare assessment methodology, suggesting that positive welfare should be evaluated on the basis of input (physical resources that are required or valued by an animal) as well as output (positive outcomes such as behavioral responses, cognitive processes and physiological markers indicative of positive affect) [ 15 ].

Experimental approaches that might allow researchers to explore animal happiness include physiological, behavioral and cognitive assessment. Yeates and Main [ 15 ] noted the utility of analyzing each source of evidence in context; for example, a behavior pattern appearing to be connected to a positive emotional experience can be corroborated by its display in appropriate contexts indicative of positive affect. Behavioral indicators of positive welfare involve activities typically performed when an animal’s affective state is positive, such as, behavioral reactions to pleasant taste, vocalizations associated with outcomes expected to entail positive affect, and facial expressions associated with positive experiences [ 15 ]. Though the facial expressions of fishes are not well studied, many species of fish are known to be capable of producing distinct vocalizations that could be useful in discerning their general affect and it is reasonable to expect the possibility that fish display a range of physical and behavioral reactions in response to pleasant sensation (including changes in facial conformation).