B.C. scientists have discovered that salmon are more aggressive in blue tanks than black ones, which could affect the success of fish farms.
Researcher Leigh P. Gaffney of the University of B.C.’s Animal Welfare Program published a study last week in the online science journal PLOS ONE on the effects of background colours on aggression in Coho salmon.
Salmon are becoming very popular in aquaculture, which involves raising fish inland in large tanks, explained study co-author Becca Franks. For reasons that aren’t clear, these tanks are almost always blue-coloured. The team wanted to see if this blue colour could affect the behaviour of the fish, as, in the wild, background colour can affect fish survival (e.g. through camouflage).
The team put 100 Coho salmon into 10 tanks and divided the tanks into different colour zones: black versus white, light grey, dark grey and patterned; and blue versus white, light and dark grey, and black. Each tank got to experience each combination.
The team found that the fish vastly preferred to hang around in darker coloured regions compared to lighter ones. Statistical analysis found that the fish preferred black backgrounds over all others, and preferred darker ones over lighter ones.
Whereas the fish normally circled the tank constantly, the fish would stop and hang around whenever they swam into a black-coloured zone, Franks said.
“I’ve been doing this (work) for over a decade and I don’t think I’ve ever seen effects this strong.”
The team also filmed the fish to track their aggression levels. They found that the fish were about four times more aggressive when in a blue area than a black one, being much more likely to chase, charge, or bite their cohorts.
Salmon rely on sight to hunt invertebrates, so the team theorized that the fish might prefer black as it makes bugs easier to spot. Fish might also see dark places as protection against predators.
Franks noted that salmon also change their colour to better fit their background and that light colouration is perceived as a sign of dominance. Blue or light backgrounds would therefore make all the salmon turn light-coloured, causing conflict as they all seem to be saying “I’m the best” to each other.
Adrian Theroux, of St. Albert’s Paradise Pets, said he was surprised by this study, as he had never heard of a link between tank background colour and aggression in fish. Colour often relates to mating, so he suspects this response may be a territorial instinct.
Franks said it’s tough to say if all fish will react to black this way, but that you could find out by colouring half of a fish tank one colour and seeing if the fish show any preference. The team suggested that farmers could influence the health of their fish through the colour of their tanks.
The study can be found at plosone.org.
A new study of depressed rats suggests that psychotherapy can overcome genetic destiny when it comes to treating mental illness.
Psychiatry professor Eva Redei and her team at Northwestern University in Chicago published a paper last week in Translational Psychiatry on how environmental enrichment affects rats that were selectively bred to be depressed.
While genetics and environmental stress are both known to cause depression in animals, researchers have yet to determine how these factors interact.
Redei said she and her team ran an experiment with two strains of rat to find out. The rats differed only in that one strain was genetically predisposed to depression.
“Rats are very good swimmers,” she said, and if you put one in a tank of water, they’ll swim around to seek an exit. A depressed rat won’t – once in the water, it’ll simply float around in despair.
Redei’s team exposed the rats to two forms of stimuli. One set was put in a sort of plastic bag straight-jacket to cause stress, and the other was let loose in a play-area stuffed with chew toys and hiding places. (Redei likened the latter to rat psychotherapy.) The team then put the rats in a tank of water to see if they would swim or float.
The team found that the depressed rats no longer acted depressed after spending time in the play-area, and instead swam around the water tank energetically. The regular rats put in the plastic bags, in contrast, acted depressed.
They also found that some, but not all, of blood biomarkers associated with depression in the rats changed as a result of their treatments. Biomarker levels in the bred-depressed rats dropped to the levels found in regular rats after time in the play-area, while levels in the regular rats became more like the bred-depressed ones after their time in the bags. Redei said this suggests that therapy can reduce the “symptoms” of gene-caused depression, but would not prevent it from being passed on to offspring.
An enriched environment is important for the mental health of any mammal, Theroux said. He breeds rats, and has found that the addition of toys and running wheels keeps them from trying to chew through their habitats.
“They’re actually quite content in their environments.”
