Bigger fish to fry: Egg position affects size and behaviour of young trout

November 28, 2012

(Phys.org)—Researchers at the University of Glasgow have discovered the behaviour and metabolism of young trout is affected by where the egg they hatched from rested in the ovaries of their mother.

Female brown trout produce many hundreds of apparently identical eggs each time they spawn. A new paper published today (Wednesday November 28) in the journal by a team from the University's Institute of Biodiversity, and shows there are subtle differences between her offspring depending on where each egg rested in the ovaries.

Eggs from the rear of the female's ovaries developed into young trout, known as fry, that were larger but had lower for their size than eggs from the front. These differences were bigger in more dominant mothers.

Position of the egg in the ovary also influenced the later behaviour of the fry, with the fish being initially more aggressive in fighting for territories if they came from the back of the ovary, although as they got older fry from the front of the ovary were most dominant.

Dr Tim Burton, who led the research, said: "These effects were really surprising. To the naked eye, fish eggs tend to look the same but it appears that there is much more going on to determine several important characteristics in trout than we have previously been aware of.

"While we don't yet know the cause of these effects, it's possible that they are due to variation in the to different parts of the ovary. We know that females deposit hormones as well as nutrients into their eggs, so it may be the case that small differences in the balance of hormones reaching the front and back of the are sufficient to generate these effects.

"The effects may be beneficial from an , since an increase in the diversity in the offspring means that the female is not putting all her eggs into one basket, so to speak, which improves the chances of her fry reaching breeding age."

The research was undertaken in collaboration with the ARC Centre of Excellence for Coral Reef Studies at James Cook University in Australia and Marine Scotland Science's Freshwater Laboratory in Pitlochry. It was funded by the Natural Environment Research Council.

Dr Burton's paper, titled 'Within-clutch differences in the phenotypes of juvenile fish depend on their location within the egg mass and maternal dominance rank', is published in Proceedings of the Royal Society B.

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