Zebrafish, a highly-social species of freshwater fish, are widely studied across many fields of laboratory science including developmental biology, neuroscience, and genomics. Nevertheless, as standard housing for zebrafish typically consists of small and simplistic environments, less is known about their social behavioral repertoire in more naturalistic settings. In particular, spontaneously occurring, socio-positive affiliative behaviors (e.g., social coordination and cohesion) that may be indicative of positive emotional experiences have rarely been reported or studied deliberately in zebrafish. Housing adult zebrafish (10 fish/tank) in large semi-natural tanks (110 L; n = 6) with sloping gravel substrate, rocks, and artificial plants, we observed a previously undescribed behavior: Distinct periods of spontaneous, synchronized, compact aggregations, what we call “heightened-shoaling”. This project aimed to quantify the characteristics of this distinctive behavior and compare parameters of heightened-shoaling to baseline periods (normal behavior) and pre-feed periods (feed-anticipatory behavior). First, across 4 days, we selected video-clips (100 s each) from within (i) instances of heightened-shoaling (n = 9), (ii) baseline periods (n = 18), and (iii) pre-feed periods (n = 18). For each of these video clips, we scan sampled every 10 s to determine fish orientations and location within the tank and agonistic behavior. Next, we used an all-occurrence sampling method to record the timing and duration of all episodes of heightened-shoaling behavior when tank-lights were on (8:00 h to 18:00 h) across 10 days. From the scan-sampling data, we found that compared to baseline periods, heightened-shoaling was characterized by increased shoal cohesion (p < 0.0001), increased adherence to the horizontal plane (p < 0.0001), decreased agonism (p < 0.0001), and no diving behavior (lower positions within the water column signal negative effect in zebrafish, p > 0.1). From the all-occurrence sampling data, we found 31 episodes of heightened-shoaling with instances observed in all six tanks and only a single case in which heightened-shoaling occurred in two tanks at the same time. The median episode duration was 7.6 min (Range 1.3–28.6). As the first systematic description of heightened-shoaling behavior, this research contributes to our knowledge of the range of zebrafish social dynamics living in naturalistic environments. Moreover, as a spontaneously occurring, protracted, affiliative behavior, heightened-shoaling appears to be a good candidate for future research into positive emotional behavior in zebrafish.

Many companion kittens entering shelters are fostered by volunteer community members during the sensitive period for socialisation (~2 to 9 weeks of age) when early experiences are critical to behavioural development. Using a mixed-method survey, we explored current fostering practices relevant to kitten behavioural development and welfare. Foster caretaker participants (n = 487) described their fostering practices and reported providing kittens with a majority of recommended socialisation experiences, such as handling and exposure to various toys and exploratory items. In open-ended text responses, foster caretakers described how they adapted socialisation practices for fearful kittens and the supports and challenges they perceived to impact their ability to properly socialise kittens. Some non-recommended techniques (e.g. flooding) were reported for socialising fearful kittens, with a decreased odds of reporting non-recommended techniques for participants with a higher level of agreeableness personality trait and an increased odds of reporting if fostering practices had been impacted by the COVID-19 pandemic. Foster caretakers reported feeling supported through shelter-supplied resources, personal knowledge, external support, and having access to socialisation opportunities; however, faced personal (e.g. time constraints), shelter-specific (e.g. lack of shelter support), and kitten-specific challenges (e.g. kitten illness). This study highlights the perspectives of foster caretakers as related to optimal socialisation, behavioural development, and welfare. To identify opportunities for improvement it is important to investigate the socialisation guidelines provided to foster caretakers, with the ultimate goal of enhancing kitten behavioural development for improved welfare, long-term adoption, and caretaker satisfaction.