Transcriptomic response to aquaculture intensification in Nile tilapia

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.

Personality profiling may help select better cleaner fish for sea-lice control in salmon farming

“…The selection of "elite" lines of cleaner fish that are particularly bold and active, but not overly aggressive, could be done in different ways. For example, one way boldness could be selected is by targeting lumpfish with high metabolic rate (Hvas et al, 2018) and low cortisol response (Gutierrez Rabadan et al, 2021), or more efficiently, by targeting genes associated with boldness and aggression (Rodriguez-Barreto et al, 2019). Metabolic rate can be used to predict boldness in some fish species (Killen et al, 2012) and can also be used to predict foraging mode (active vs passive) in lumpfish (Killen et al, 2007a).…”

“…For example, feeding sea-lice and live prey to lumpfish prior to cage deployment was found to promote subsequent delousing behaviour (Imsland et al, 2019a), and previous exposure to salmon may also reduce stress and improve cohabitation (Staven et al, 2019). In general, intensive fish farming seems to modify fish behaviours in predictable ways, by altering patterns of gene expression in the fish brain that can be targeted by selective breeding (Rodriguez-Barreto et al, 2019). Social enrichment prior to deployment in sea cages could be used to modify behaviours and facilitate adaptation of lumpfish to sea cages.…”

“…As a measure of boldness, we counted the number of times individuals were within 10 cm of the novel object phase 4 (novel), the time latency to first approach the novel object, and average distance (cm) from novel object at one minute intervals, as these are measures of neophobia that map well into the boldness-shyness continuum (Champneys et al, 2018). Collectively, these metrics capture variation in five dimensions of fish personality and have been associated with the expression of particular genes in the fish brain (Champneys et al, 2018;Rodriguez-Barreto et al, 2019). We also measured body mass (g) and calculated specific growth rate (SGR%, (Lugert et al, 2016) between the first and second repeated trials to account for the influence of feeding motivation on behaviour.…”

“…Anxiety was assessed by recording the total time spent within 10cm of the tank walls (thigmotaxis) during phase 1 (neutral) and also the total time spent within 10cm of the black panel in phase 2 (shelter), as both are established methods of assessing anxiety in fish (Cianca et al, 2013;Godwin et al, 2012). To score aggression, we counted the number of agonistic actions (nips and charges) directed towards the mirror image (Rodriguez-Barreto et al, 2019) during phase 3 (mirror). The number of approaches to the mirror that did not result in body contact, as well as the time spent within close proximity (<10 cm) of the mirror during this phase were used as measures of sociality (Cattelan et al, 2017).…”

Early life stress causes persistent impacts on the microbiome of Atlantic salmon

“…In intensive aquaculture, fish are often reared at unnaturally high densities and exposed to a range of other handling and social stressors, which can induce adverse health effects such as impaired growth and fitness, altered behaviour and depressed immunity (Conte 2004; Ellison et al 2018; Iwama et al 2011; Rodriguez-Barreto et al 2019). Some evidence indicates that aquaculture related stressors can alter fish microbiome diversity and structure (Boutin et al 2013; Ringø et al 1997; Zha et al 2018).…”