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Density-dependent changes in neophobia and stress-coping styles in the world's oldest farmed fish.

ABSTRACT: Farmed fish are typically reared at densities much higher than those observed in the wild, but to what extent crowding results in abnormal behaviours that can impact welfare and stress coping styles is subject to debate. Neophobia (i.e. fear of the 'new') is thought to be adaptive under natural conditions by limiting risks, but it is potentially maladapted in captivity, where there are no predators or novel foods. We reared juvenile Nile tilapia (Oreochromis niloticus) for six weeks at either high (50 g l-1) or low density (14 g l-1), assessed the extent of skin and eye darkening (two proxies of chronic stress), and exposed them to a novel object in an open test arena, with and without cover, to assess the effects of density on neophobia and stress coping styles. Fish reared at high density were darker, more neophobic, less aggressive, less mobile and less likely to take risks than those reared at low density, and these effects were exacerbated when no cover was available. Thus, the reactive coping style shown by fish at high density was very different from the proactive coping style shown by fish at low density. Our findings provide novel insights into the plasticity of fish behaviour and the effects of aquaculture intensification on one of the world's oldest farmed and most invasive fish, and highlight the importance of considering context. Crowding could have a positive effect on the welfare of tilapia by reducing aggressive behaviour, but it can also make fish chronically stressed and more fearful, which could make them less invasive.

SUBMITTER: Champneys T

PROVIDER: S-EPMC6304122 | biostudies-literature | 2018 Dec

REPOSITORIES: biostudies-literature

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Density-dependent changes in neophobia and stress-coping styles in the world's oldest farmed fish.

Champneys T T Castaldo G G Consuegra S S Garcia de Leaniz C C

Royal Society open science 20181212 12

Farmed fish are typically reared at densities much higher than those observed in the wild, but to what extent crowding results in abnormal behaviours that can impact welfare and stress coping styles is subject to debate. Neophobia (i.e. fear of the 'new') is thought to be adaptive under natural conditions by limiting risks, but it is potentially maladapted in captivity, where there are no predators or novel foods. We reared juvenile Nile tilapia (<i>Oreochromis niloticus</i>) for six weeks at ei ...[more]

PMID: 30662751

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Project description:Individual stress coping style has profound effects on how animals respond to environmental change, and individuals within a population strikingly differ in how gene expression shifts in response to challenge. This study used a wild type Zebrafish (Danio rerio) population to: 1) identify and screen for individual coping style using a screening protocol for risk taking in groups and 2) do global transcriptomics of brains from proactive, reactive or randomly chosen individuals (n=10/group) under control conditions. Results show that within our population proactive and reactive individual coping styles can be accurately identified and may represent 10-30% of individuals within the population. Microarray data analyses identify fundamental differences between the three different groups where variance in gene expression values are reduced by using coping style as an explanatory variable. Furthermore, significant differences in mRNAs and related biological processes suggest that even under identical environmental conditions the molecular mechanisms that underpin physiological processes are very different between proactive and reactive individuals within a population. Experimental tank was an 18 litre glass aquarium (dimensions (LxWxH): 40 X 25 X 20cm) lined on three sides with white paper; the front wall was not covered to allow the observer to record the behaviour and divided at 1/3 of his length with a black PVC screen with a 3cm diameter hole in the middle. All the tank surfaces around this third area of the tank were covered with dark paper and closed on the upper part with a removable lid to provide a shelter for the animals. The hole was covered with the same PVC plastic material and removed once the screening started to allow the fish enter the novel environment. Food was not supplied the day before to ensure that during the test the fish were hungry and they had to make the decision to leave a safe area in order to forage. Boldness was measured as the time taken by individual fish to leave a group from a safe, darkened area. It hence represents the willingness of a fish to explore a new, potentially dangerous environment, or boldness. Tests were conducted with groups of 9 randomly-selected fish from stocking tanks. Fish were familiar to each other in the sense that they were previously held in the same stocking tank. Test started with a 10 min. habituation period in the sheltered area with the hole closed with a PVC screen and the top of the sheltered area of the tank also covered to provide a complete quiet place. Then the lid covering the hole was gently removed. Either the first 3 fish to exit the shelter or fish with latency times inferior to 10 minutes were considered bold fish and were removed gently with a fish net from the test tank and placed apart in another tank. Latency times of emergency from the sheltered area were recorded individually. Next 3 animals to emerge before 15 minutes were considered intermediate and also removed gently. At the end of this last 15 minutes, animals that still remained inside the sheltered area were considered shy. Intermediates were discarded and fish selected for different coping strategies where placed in different tanks for posterior molecular analysis. Selected animals were killed by an overdose of MS-22 and the brains were sampled. Individual tissue samples were homogenized into 0.3 ml of Tri-Reagent and stored at -80C for further molecular analysis.

Dataset Information

Density-dependent changes in neophobia and stress-coping styles in the world's oldest farmed fish.

Publications

Density-dependent changes in neophobia and stress-coping styles in the world's oldest farmed fish.

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