Preference and Motivation Tests for Body Tactile Stimulation in Fish

Abstract

We tested whether territorial fish (Nile tilapia) perceive body tactile stimulation as a positive or negative resource. Individual male fish were placed for eight days in an aquarium containing a rectangular PVC frame, which was filled with vertical plastic sticks sided with silicone bristles in the middle of the tank. Fish passing this device received a tactile stimulus. The fish then underwent a preference test by choosing between areas half-with and half-without tactile bristles. Then, fish were submitted to a motivation test where they had to pass an aversive stimulus (bright light) to access the device. Fish were, then, paired to settle social rank, which occurs by way of fights (social stressor), and were assigned again to preference and motivation tests. A group without social stress was used as a control. Contrary to our expectations, fish preferred the area without tactile bristles, although subordinate fish reached tactile stimulation more than the dominant one. Social stress did not affect the preference and motivation, suggesting that fish do not perceive tactile stimulation as a stressor reliever. However, as fish did not avoid the stimulation, reached the device spontaneously, and faced an aversive stimulus to access it, we conclude that tactile stimulation is not a negative condition and, therefore, can be used in further studies regarding fish welfare.

Environmental enrichment in fish aquaculture: A review of fundamental and practical aspects

“…salmonids) or not, remains to be proven. Recent studies on Nile tilapia suggest that, although tactile stimulation does not lower blood cortisol levels in the short‐term, it can reduce aggressiveness 204,205 and may also reduce the overall stress associated with social interactions in long‐term. Moreover, a recent study reported that koi carp ( Cyprinus rubrofuscus ) showed interest in physical contact (tactile interaction) with humans, suggesting that interacting with human skin, a novel substance and texture, might serve as a source of tactile and/or sensory enrichment 206 .…”

“…Moreover, a recent study reported that koi carp ( Cyprinus rubrofuscus ) showed interest in physical contact (tactile interaction) with humans, suggesting that interacting with human skin, a novel substance and texture, might serve as a source of tactile and/or sensory enrichment 206 . However, further studies are still needed to test several effects of tactile stimulation on fish welfare 205 …”

Long-term body tactile stimulation reduces aggression and improves productive performance in Nile tilapia groups

“…They also demonstrated their motivation to achieve TS. Nonetheless, the frequency of choice for an area without bristles is higher 12 . Thus, the silicone bristles may have caused some resistance, making it easier for the fish to pass through open control areas.…”

“…TS-treated fish crossed the respective TS apparatus less than the control fish, which could be seen as an aversive reaction to such a device. However, while testing the efficiency of a similar apparatus, Gauy et al 12 had shown that Nile tilapia males spontaneously chose to pass through the bristles despite having the option to avoid them. They also demonstrated their motivation to achieve TS.…”

“…This apparatus was previously tested to ensure that neither the mucus lining of the subjects was removed, nor any injury caused to their bodies 12,26 . Furthermore, Nile tilapia spontaneously chose to cross through this type of apparatus and overcomes an aversive bright-light rout, showing motivation to access it 12 , thus ensuring its suitability for testing further hypothesis regarding TS in fish. The experiment lasted for 21 days.…”