DIFFERENT EFFECTS OF BODY TACTILE STIMULATION ON THE WELFARE OF THE ORNAMENTAL ANGELFISH AND THE SIAMESE FIGHTING FISH

Introduction

Aquaculture of ornamental fish is among the fastest-growing activities worldwide. Nevertheless, the several stages of the ornamental fish trade can impair fish welfare, from initial capture to final housing. In this context, environmental enrichment is a key approach to mitigate such negative impacts, particularly in housing aquaria. Recently, body tactile stimulation (TS), akin to gentle touch or therapeutic massage, has emerged as a promising tool of sensory enrichment for fish. Studies have shown that artificial TS reduces stress in reef species (Soares et al., 2011), diminishes fear in zebrafish (Schirmer et al., 2013), and limits aggression while promoting growth in Nile tilapia (Gauy et al., 2022; 2023). Considering that enrichment can affect species differently, we evaluated the effects of TS on aggressive behavior and stress in two widely reared ornamental species, the Siamese fighting fish (Betta splendens) and the cichlid angelfish (Pterophyllum scalare). Given that monoamines mediate TS mechanisms in vertebrates, we also investigated the association between TS and brain Dopamine (DA) and serotonin (5-HT) levels, specifically in B. splendens.

Methods

Fish were exposed for 22 days to either an artificial TS apparatus or to an identical one without bristles, serving as a control (Fig. 1). Then, we evaluated individual aggressive behavior using mirror tests and pair fights, and stress by cortisol levels in both species. Brain DA, 5-HT, and their metabolites were measured by HPLC only in B. splendens due to logistical reasons.

Results and discussion

TS reduced aggression in male angelfish without altering cortisol levels, whereas in B. splendens, it increased restrained fighting and cortisol levels. Brain monoamines analysis in B. splendens revealed decreased 5-HT and increased 5HIAA/5HT turnover. DA levels remained unchanged, indicating no activation of the neural reward pathway. These contrasting outcomes may reflect species-specific differences in ecological history and behavioral traits. P. scalare, for instance, inhabits macrophyte-rich environments where substrate contact is frequent. Conversely, artificial selection for heightened aggressiveness or prolonged social isolation may render TS stressful rather than rewarding for B. splendens. Overall, our findings suggest that the efficiency of tactile enrichment is species-dependent, highlighting the importance of tailoring welfare interventions accordingly.

Figure 1 – Tactile stimulation. The TS apparatus consisted of a rectangular PVC frame filled with vertical plastic sticks, with silicone bristles on their sides that promote TS (A), and without silicone bristles for control (B). Both apparatuses were placed in the middle of the tank, and fish received TS when passing through the bristles (C). N = 20 per treatment, per species.

Acknowledgment

This study was supported by the São Paulo Research Foundation (FAPESP) [Grants to EGF # 2023/02306-1; scholarship for BCS #2023/04059-1, post-doc scholarship for ACSG #2023/09880-5], CAPES scholarship for SGP #001]. MCS is supported by the Foundation for Science and Technology (FCT), Portugal (CEEC Individual-2021.01458.CEECIND/CP1668/CT0003).

References

Gauy, A. C. S., Bolognesi, M. C., & Gonçalves-de-Freitas, E. (2022). Long-term body tactile stimulation reduces aggression and improves productive performance in Nile tilapia groups. Scientific Reports, 12(1), 20239.

Gauy, A. C. S., Bolognesi, M. C., & Gonçalves-de-Freitas, E. (2023). Body tactile stimulation reduces the effects of high stocking density on the welfare of Nile tilapia (Oreochromis niloticus). Fishes, 8(6), 320.

Schirmer, A., Jesuthasan, S., & Mathuru, A. S. (2013). Tactile stimulation reduces fear in fish. Frontiers in behavioral neuroscience, 7, 167.

Soares, M. C., Oliveira, R. F., Ros, A. F., Grutter, A. S., & Bshary, R. (2011). Tactile stimulation lowers stress in fish. Nature Communications, 2(1), 534.