Abstract

To meet future global demand for fish protein, more fish will need to be farmed using fewer resources, and this will require the selection of nonaggressive individuals that perform well at high densities. Yet, the genetic changes underlying loss of aggression and adaptation to crowding during aquaculture intensification are largely unknown. We examined the transcriptomic response to aggression and crowding in Nile tilapia, one of the oldest and most widespread farmed fish, whose social structure shifts from social hierarchies to shoaling with increasing density. A mirror test was used to quantify aggression and skin darkening (a proxy for stress) of fish reared at low and high densities, and gene expression in the hypothalamus was analysed among the most and least aggressive fish at each density. Fish reared at high density were darker, had larger brains, were less active and less aggressive than those reared at low density and had differentially expressed genes consistent with a reactive stress‐coping style and activation of the hypothalamus–pituitary–interrenal (HPI) axis. Differences in gene expression among aggressive fish were accounted for by density and the interaction between density and aggression levels, whereas for nonaggressive fish differences in gene expression were associated with individual variation in skin brightness and social stress. Thus, the response to crowding in Nile tilapia is context dependent and involves different neuroendocrine pathways, depending on social status. Knowledge of genes associated with the response to crowding may pave the way for more efficient fish domestication, based on the selection of nonaggressive individuals with increasing tolerance to chronic stress necessary for aquaculture intensification.

Highlights

  • Fish domestication is thought to be constrained by the capacity of individuals to adapt to high densities in captivity (Ashley, 2007; Huntingford & Adams, 2005), and our study shows that one con‐ sequence of crowding in Nile tilapia is the inhibition of aggression, a process that we found was associated with the expression in the hypothalamus of stress‐related genes

  • Our results suggest the existence of two types of stress in tilapia: social stress caused by the formation of social hierarchies maintained by agonistic interactions at low density and chronic stress caused by crowding at high density

  • Our study indicates the crowding inhibits aggressive behaviour in Nile tilapia and results in changes in the expression of stress‐re‐ lated genes that accompany the shift from social hierarchies main‐ tained by agonistic interactions at low density, to shoaling at high density

Read more

Summary

| MATERIAL AND METHODS

A total of 360 mixed‐sex three‐week‐old Nile tilapia (O. niloticus, sil‐ ver strain) were sourced from a commercial supplier (Fishgen Ltd) which employs communal tank spawning, typically involving four sires and 12–15 dams per spawning tank. As recommended for such cases within DESeq analysis (Love et al, 2014), we modelled gene expres‐ sion separately for the two heterogenous groups (most aggressive and least aggressive fish) using density, number of attacks and skin brightness (and their interactions) as predictors. Aggression, measured as number of agonistic interactions against the mirror, was unrelated to body mass (p = 0.750) or sex (p = 0.514), but fish reared at low density were significantly more aggressive (mean number of interactions = 28.63, SE = 5.93) than those reared at high density (mean number of interactions = 7.11, SE = 2.09), while statistically controlling for tanks effects (GLMM estimate for low density = 3.103, SE = 0.887, z = 3.498, p < 0.001; Figure 3c).

| DISCUSSION
Findings
| CONCLUSIONS
CONFLICT OF INTEREST
Full Text
Published version (Free)

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call