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

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.

Prospects for Genetic Improvement in Objective Measurements of Body Colour in Pacific Whiteleg Shrimp (Litopenaeus vannamei)

“…This is partially due to the unavailability of efficient measurement methods. Besides the subjective measurements of shrimp colour by observation, previous studies in laboratory have used the roche colour card, digital camera [6,7,10], or a combination of both roche colour card and laminated paper for hue measurements [11,12], and/or using computer tomography [13]. Some other methods can measure pigmentation, such as high performance liquid chromatography; thin layer liquid chromatography; spectrophotometry; colorimetry; digital imaging acquisition; and, processing [14].…”

Positive Welfare for Fishes: Rationale and Areas for Future Study

“…One recent study used a preference index to assess Nile tilapias' (Oreochromis niloticus) motivation over time for different tank wall colors [32] and other work has shown that male tilapia's (O. mossambicus) substrate preference is conditional on social context [33]. Similarly, other work has shown that Coho salmon (Oncorhynchus kisutch) have a strong preference to be in environments with dark backgrounds and, when restricted to lighter backgrounds, are four times more aggressive than when they have access to dark backgrounds [34].…”

Maturation of behaviour in the fathead minnow

“…Application of different background colors was recently investigated. For example, Gaffney et al (2016), analyzed background color effects on aggressiveness in Coho salmon (Oncorhynchus kisutch) in aquaculture. In the current study, this test was used to determine light-dark preference in fathead minnows at different ages with the aim of developing the test for use in an ecotoxicological context later on to determine if exposure to toxicants can affect light-dark preference behaviour.…”