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Coho Salmon (Oncorhynchus kisutch) Prefer and Are Less Aggressive in Darker Environments.

Gaffney LP, Franks B, Weary DM, von Keyserlingk MA - PLoS ONE (2016)

Bottom Line: Fish are capable of excellent vision and can be profoundly influenced by the visual properties of their environment.Moreover, having darker backgrounds in the environment resulted in less aggressive behaviour throughout the tank (p < 0.0001).These results provide the first evidence that darker tanks are preferred by and decrease aggression in salmonids, which points to the welfare benefits of housing farmed salmon in enclosures containing dark backgrounds.

View Article: PubMed Central - PubMed

Affiliation: Animal Welfare Program, Faculty of Land and Food Systems, University of British Columbia, 2357 Main Mall, Vancouver, BC, V6T 1Z6, Canada.

ABSTRACT
Fish are capable of excellent vision and can be profoundly influenced by the visual properties of their environment. Ambient colours have been found to affect growth, survival, aggression and reproduction, but the effect of background darkness (i.e., the darkness vs. lightness of the background) on preference and aggression has not been evaluated systematically. One-hundred Coho salmon (Oncorhynchus kisutch), a species that is increasing in popularity in aquaculture, were randomly assigned to 10 tanks. Using a Latin-square design, every tank was bisected to allow fish in each tank to choose between all the following colour choices (8 choices in total): black vs. white, light grey, dark grey, and a mixed dark grey/black pattern, as well as industry-standard blue vs. white, light grey, dark grey, and black. Fish showed a strong preference for black backgrounds over all other options (p < 0.01). Across tests, preference strength increased with background darkness (p < 0.0001). Moreover, having darker backgrounds in the environment resulted in less aggressive behaviour throughout the tank (p < 0.0001). These results provide the first evidence that darker tanks are preferred by and decrease aggression in salmonids, which points to the welfare benefits of housing farmed salmon in enclosures containing dark backgrounds.

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Related in: MedlinePlus

Salmon prefer darker backgrounds.Preference strength increased with increasing background darkness (p < 0.0001). For the (a) black-trials and (b) blue-trials, dots represent each tank’s average number of Coho salmon (Oncorhynchus kisutch) located on the comparison side. Background darkness ranges from 0 (white) to 1 (black). Large symbols represent average values across all tanks (n = 10) with the fill colour corresponding to the background darkness of the comparison side (white, light grey, dark grey, or black) and the triangle (▿) indicating the patterned background trial.
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pone.0151325.g001: Salmon prefer darker backgrounds.Preference strength increased with increasing background darkness (p < 0.0001). For the (a) black-trials and (b) blue-trials, dots represent each tank’s average number of Coho salmon (Oncorhynchus kisutch) located on the comparison side. Background darkness ranges from 0 (white) to 1 (black). Large symbols represent average values across all tanks (n = 10) with the fill colour corresponding to the background darkness of the comparison side (white, light grey, dark grey, or black) and the triangle (▿) indicating the patterned background trial.

Mentions: Pair-wise comparisons for the black-trials revealed a strong preference for black background over all other options (black vs. white: t(9) = 41.24, p < .0001; black vs. light grey: t(9) = 11.88, p < 0.0001; black vs. dark grey: t(9) = 12.11, p < 0.0001; black vs. pattern: t(9) = 3.66, p < .01; Fig 1a). In the blue-trials, fish showed no preference for white vs. blue (t(9) = 0.47, p > 0.6), a tendency to prefer light grey over blue (t(9) = 2.22, p < 0.1), and a preference for both dark grey and black over blue (t(9) = 5.63, p < 0.001, and t(9) = 13.06, p < 0.0001, respectively; Fig 1b). Across all trials, we found that preference strength increased with background darkness (t(67) = 8.81, p < 0.0001, Fig 1a and 1b). We found limited evidence that the patterned background was preferred beyond what would be expected based on its darkness value alone (t(67) = 1.92, p = 0.06, Fig 1b).


Coho Salmon (Oncorhynchus kisutch) Prefer and Are Less Aggressive in Darker Environments.

Gaffney LP, Franks B, Weary DM, von Keyserlingk MA - PLoS ONE (2016)

Salmon prefer darker backgrounds.Preference strength increased with increasing background darkness (p < 0.0001). For the (a) black-trials and (b) blue-trials, dots represent each tank’s average number of Coho salmon (Oncorhynchus kisutch) located on the comparison side. Background darkness ranges from 0 (white) to 1 (black). Large symbols represent average values across all tanks (n = 10) with the fill colour corresponding to the background darkness of the comparison side (white, light grey, dark grey, or black) and the triangle (▿) indicating the patterned background trial.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4814047&req=5

pone.0151325.g001: Salmon prefer darker backgrounds.Preference strength increased with increasing background darkness (p < 0.0001). For the (a) black-trials and (b) blue-trials, dots represent each tank’s average number of Coho salmon (Oncorhynchus kisutch) located on the comparison side. Background darkness ranges from 0 (white) to 1 (black). Large symbols represent average values across all tanks (n = 10) with the fill colour corresponding to the background darkness of the comparison side (white, light grey, dark grey, or black) and the triangle (▿) indicating the patterned background trial.
Mentions: Pair-wise comparisons for the black-trials revealed a strong preference for black background over all other options (black vs. white: t(9) = 41.24, p < .0001; black vs. light grey: t(9) = 11.88, p < 0.0001; black vs. dark grey: t(9) = 12.11, p < 0.0001; black vs. pattern: t(9) = 3.66, p < .01; Fig 1a). In the blue-trials, fish showed no preference for white vs. blue (t(9) = 0.47, p > 0.6), a tendency to prefer light grey over blue (t(9) = 2.22, p < 0.1), and a preference for both dark grey and black over blue (t(9) = 5.63, p < 0.001, and t(9) = 13.06, p < 0.0001, respectively; Fig 1b). Across all trials, we found that preference strength increased with background darkness (t(67) = 8.81, p < 0.0001, Fig 1a and 1b). We found limited evidence that the patterned background was preferred beyond what would be expected based on its darkness value alone (t(67) = 1.92, p = 0.06, Fig 1b).

Bottom Line: Fish are capable of excellent vision and can be profoundly influenced by the visual properties of their environment.Moreover, having darker backgrounds in the environment resulted in less aggressive behaviour throughout the tank (p < 0.0001).These results provide the first evidence that darker tanks are preferred by and decrease aggression in salmonids, which points to the welfare benefits of housing farmed salmon in enclosures containing dark backgrounds.

View Article: PubMed Central - PubMed

Affiliation: Animal Welfare Program, Faculty of Land and Food Systems, University of British Columbia, 2357 Main Mall, Vancouver, BC, V6T 1Z6, Canada.

ABSTRACT
Fish are capable of excellent vision and can be profoundly influenced by the visual properties of their environment. Ambient colours have been found to affect growth, survival, aggression and reproduction, but the effect of background darkness (i.e., the darkness vs. lightness of the background) on preference and aggression has not been evaluated systematically. One-hundred Coho salmon (Oncorhynchus kisutch), a species that is increasing in popularity in aquaculture, were randomly assigned to 10 tanks. Using a Latin-square design, every tank was bisected to allow fish in each tank to choose between all the following colour choices (8 choices in total): black vs. white, light grey, dark grey, and a mixed dark grey/black pattern, as well as industry-standard blue vs. white, light grey, dark grey, and black. Fish showed a strong preference for black backgrounds over all other options (p < 0.01). Across tests, preference strength increased with background darkness (p < 0.0001). Moreover, having darker backgrounds in the environment resulted in less aggressive behaviour throughout the tank (p < 0.0001). These results provide the first evidence that darker tanks are preferred by and decrease aggression in salmonids, which points to the welfare benefits of housing farmed salmon in enclosures containing dark backgrounds.

Show MeSH
Related in: MedlinePlus