Abstract
Dominance is defined as the preferential access to limited resources. The present study aimed to characterise dominance in a non-aggressive flatfish species, the Senegalese sole (Solea senegalensis) by 1) identifying dominance categories and associated behaviours and 2) linking dominance categories (dominant and subordinate) with the abundance of selected mRNA transcripts in the brain. Early juveniles (n = 74, 37 pairs) were subjected to a dyadic dominance test, related to feeding, and once behavioural phenotypes had been described the abundance of ten selected mRNAs related to dominance and aggressiveness was measured in the brain. Late juveniles were subjected to two dyadic dominance tests (n = 34, 17 pairs), related to feeding and territoriality and one group test (n = 24, 4 groups of 6 fish). Sole feeding first were categorized as dominant and sole feeding second or not feeding as subordinate. Three social behaviours (i. “Resting the head” on another fish, ii. “Approaching” another fish, iii. “Swimming above another” fish) were associated with dominance of feeding. Two other variables (i. Total time occupying the preferred area during the last 2 hours of the 24 h test, ii. Organisms occupying the preferred area when the test ended) were representative of dominance in the place preference test. In all tests, dominant fish compared to subordinate fish displayed a significantly higher number of the behaviours “Rest the head” and “Approaches”. Moreover, dominant sole dominated the sand at the end of the test, and in the group test dominated the area close to the feed delivery point before feed was delivered. The mRNA abundance of the selected mRNAs related to neurogenesis (nrd2) and neuroplasticity (c-fos) in dominant sole compared to subordinate were significantly different. This is the first study to characterise dominance categories with associated behaviours and mRNA abundance in Senegalese sole and provides tools to study dominance related problems in feeding and reproduction in aquaculture.
Highlights
Behavioural studies in fish have been used as a model background in the field of perceptive ethology/evolutionary psychology
The trend in late juveniles was similar to that observed in early juveniles, with similar levels of variation in the behaviours and dominant late juveniles (n = 17 of 34) displayed less variability (Approaches = 18.9 ± 2.6 counts; CV = 56.4%; Swim above another” (SAA) = 27.3 ± 9.5 counts; CV = 144.3%; rested the head (RTH) = 9.1 ± 1.4 counts; CV = 65.9%) than subordinates (n = 17 of 34)
The present study has shown that Senegalese sole can be categorized for different social status: (a) when competition was observed between pairs and in groups, (b) in relation to both feeding response and place preference tests, and (c) at different juvenile stages, from early juvenile, when fish weight was approximately 100 g, to late juvenile that weighted approximately 300 g
Summary
Behavioural studies in fish have been used as a model background in the field of perceptive ethology/evolutionary psychology. Associating several cognitive traits (memory, kin recognition and learning, among others) with morphology, ecology and a variety of behavioural parameters could provide a general vision for cognitive ethology [1,2,3,4]. The study of flatfish behaviour has attracted the attention of researchers due to their ecology, life history and adaptations. When considered in comparison with pelagic fish species, flatfish behaviour has received little attention. Dominance behaviour in flatfish has not been described. The understanding of flatfish dominance behavioural patterns would be very useful to comprehend the biology and ecology of flatfish species and for stock management in aquaculture and natural populations
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